Not to dispute your findings but perhaps I can add here... the entire notion of "split-phase" is very easy to misunderstand. Yes, there is only a single phase entering your home but the 120V loads in the home are basically "split" in half. As far as the loads in the home are concerned, L1 and L2 are indeed 180° out-of-phase with each other WHEN REFERENCED TO NEUTRAL. Yes, each of the halves of the "split-phase" system are "in-phase" with each other (adding) when measured from L1 to L2 but when voltage is measured from the "Neutral" reference to L1 and then from Neutral to L2 the resultant measurement shows that L1 and L2 are indeed 180° out-of-phase WITH REFERENCE TO NEUTRAL. This is done so that 120V loads can share a common "Neutral" and the shared currents in that Neutral end up opposing each other because at any given instant, the currents between L1 and L2, each being 180° out of phase with one other are actually flowing in opposite directions in the Neutral leg. The result is that the currents algebraically sum together in the Neutral line resulting in a net Zero current (if the loads between L1 and L2 are perfectly balanced). In practice there is a non-zero current flowing in the Neutral but it is always less than the currents flowing in either L1 or L2. This is why electricians try to "balance" the load center, dividing household loads somewhat equally between L1 and L2. It is all about perspective or "reference" when measuring voltages in any system. You are measuring a voltage against a "reference" and in this case, the 120V, L1 and L2 loads in the home are referenced to Neutral.
I don't have any issue with what you just said, I agree completely. The key is that bit about "with reference to neutral." Voltage, being a relative measurement, always must have a reference, and for residential power that reference is almost always ground/neutral (not interested in getting into the weeds about the difference between the two at this tine). So it is intuitive to think of L1 and L2 being out of phase because that's how it looks on a ground-referenced scope. But to say "out of phase," without the stipulation of "with reference to neutral" to qualify it as a relative measurement, is to assert a non-relative reality. What people are saying when they say "out of phase" and stop there without specifying it as a relative voltage measurement, is that the two halves of the transformer are physically out of phase. That misstatement is what I take exception to, especially since it seems to me that most of the people saying it don't realize that it's a misstatement and will even try to battle you over the matter.
@@charlesstaton8104 I agree with that entirely. It is the "two halves of the transformer being out-of-phase with each other" idea that I think folks have a hard time with. Thank you for your work and video's, good information.
The fact that the neutral currents nullify one another from equally loaded L1 - L2 120v branches should lead the reader to question the concepts being discussed. Polarity inversion and 180° phase difference are the same thing.... Period. This respondent correctly addressed the issue at hand "how are we referencing the measurement?".
@@charlesstaton8104 How exactly do electrons flow in a split phase system? No matter which way it is, there has to be at least 2 conductors where electrons are flowing to the load simultaneously at any given time right, so if that is true then how would there be voltage across those 2 lines at that moment? Im genuinely curious and am having a difficult time understanding
@@FearfulFellow Electron flow is something I never found any practical reason to study. I don't know enough about it to give you the kind of answer you're probably looking for. There is however a practical reason for understanding the difference between two waves that are actually out of phase and waves that only appear out of phase because of where you measure them, and that's all this video was meant to address. Electron flow is more abstract and academic and I have no plans on covering it.
@@kjellg6532 in reality its one sine referenced at different points, in this case to a center tap, to itself. when playing with a scope you realize the second wave is simply the opposite swing of the same wave referenced. In short its the same wave looked at in different angles.... your up is chinas down but in reality its just down, to each persons reference
@@charlesstaton8104 a 5000 watt inverter with expandable battery capacity (not split phase just one inverter) with 2 120v 30 amp outlets. I was looking to see if I can run leg 1 off of one outlet then leg 2 off the other outlet to the 240v mini split. The mini split has an inverter to DC to run the compressor motor and the fan motors. Sorry if this is confusing.
@@ryanevans7253 i don't have enough information to answer. It has 2 outlets but they might just wired in parallel inside. It might only output a single 120V. You might want to ask the manufacturer. Or tell me the model # and I will look it up later (out of time for now).
Nope, I didn’t skip any of it. I saw you state lots of stuff that, while technically correct, in the real world is not valid. Then, almost as an aside, tell people not to do it. My point was, it’s not a valid measurement for the vast majority of technicians who may be watching, let alone the diy brigade. I’m pretty sure you’ll find you absolutely can treat L1 as a source and run all your loads between that and neutral. Please don’t though. Your power company won’t like it, any more than they would an unbalanced 3 phase supply.
The reason I made the video is because the "technically correct" part seems to be glossed over by many educational resources and therefore unknown by a lot of (maybe most?) people. Loads of people think L1 and L2 *actually are* out of phase, and defend that idea with an unreasonable level of zeal. Treating L1 and L2 as being out of phase or opposite polarity might not cause you to get wrong answers on a test over Kirchoff's laws, but it leads to further misconceptions, like that current flows opposite directions through the loads on L1 and the loads on L2. Do you realize how many people actually think that? If you're of the opinion that I'm being pedantic and making something out of nothing, try asking around to different people you know (electricians, technicians, electronics engineers with 40+ years of experience) about the direction of current flow through L1 and L2 loads; I think you will be appaled.
By your incorrect theory, L to L would only ever be 120v. If you set your scope to trigger on CH1 and put one probe on L1 and one probe on L2, you'd see that when L1 is 120v peak above 0, L2 would be 120v peak below 0. L to L is 240v peak. Your arbitrary changing of reference to suit your theory is incorrect.
Let's say there are six 6V batteries in series, but you can't see the polarity. There is no ground, no predefined reference point. You measure from end to end, and you get 36V. From this measurement alone you have proof that all six batteries are connected with the same polarity because their voltage adds. If one of them were connected with opposing polarity, it would subtract 6V from the total, leaving 24V. If two were opposing, 12V. If 3 (HALF) were opposing, you would get 0V. You can do the same experiment with AC sources instead of DC sources. Instead of six 6V batteries, use six 6V isolation transformers. Again, if the six transformer secondaries are all connected with same polarity, the total voltage will be 36VAC. If one is reversed (AKA out of phase) then the total voltage will be 24VAC and if two are reversed (AKA out of phase) then the total will be 12VAC. And if 3 (HALF) of the source is reversed (AKA out of phase) then the overall voltage will be 0V. We know just by the fact that that sources add, that they are IN PHASE with each other. Choosing one specific reference point and calling it the holy reference point and refusing to ever take any or acknowledge any other measurements with reference to any point other that the holy reference point does not change that. Just because the waves *_appear_* inverse on your scope screen does not mean that they *_are_* inverse. They only *_appear_* that way *_because_* of the insistence on using the center tap of the transformer as reference. The same thing would happen in the six-battery series string if you welded your black meter probe to the jumper between battery #3 and battery #4. Batteries to the left would *_appear_* to be "negative" while batteries to the right *_appear_* to be positive. This can be harder to conceptualize when there are only two halves to measure instead of six separate sources which is why I bring up six sources. But hopefully it is obvious that they are equivalent, whether six or two, and whether AC or DC. If half of the source is inverted then the total is 0v, while if it is non-inverted then (regardless of appearance which is purely a function of chosen reference) they add. If they add then it is impossible that they are anything other than in-phase AKA same polarity.
I am well aware of the confusion our residential system has caused some and while I feel I have a pretty solid handle on it I thought maybe someone had rediscovered the wheel in explaining it. A few minutes in the video it started reminding of the super geeks in college getting into rage'rs over simple concepts like semantics. Thinking I was missing the brilliance, half way through I moved on and I casually listened while reading comments. This effort provided no additional sense of discovery and it became clear this video was just a muddy mess of an effort of trying to hard. Fortunately I read @Brokendiode (Retired Engineer) about half way down and his comments made me realize the audio had ended, reading the rest of the comments wasn't going to provide the eureka moment and I wasn't crazy. Look, there is a reason the white neutral in a 3 wire multiwire branch circuit is the same size as the Black L1 and Red L2 and NOT twice the size. And it's the same reason why older (mechanical) 240v stoves, dryers, pumps etc didn't even have neutrals. The return bath in each of the circuits is the other hot leg. Black returns on the red, red returns on the black. They are each others neutral because they are OUT of phase. Now they couldn't function that way if they were in phase. If you doubt that and are insistent they ARE in phase, it's pretty simple to test your theory. Open your panel, find a DPST breaker. Remove the red conductor and land it on the next breaker down (it will have a black). Close both circuits. How did that work out for you? (I'm not responsible if your theory has unexpected results.) Guys, this is not rocket science. N to B and N to R are 180 out of phase. The only way B and R can be measured IN phase is if you move your reference across the windings. Measuring N to B and R to N would be in phase. Of course this would just be an academic exercise as nothing is wired this way and therefore has no practical application.
Let’s do a simple explanation here. I’m going to assume that you know complex numbers. Let’s assume that you claim that L1 and L2 are out of phase. So let L1 = 120( cos(0°) + j_sin(0°) ) = 120. Let L2 = 120( cos(180°) + j_sin(180°) ) = -120. The j_ denotes a complex part and since the sine of 0° or 180° will be 0 then we don’t have to consider it. Adding them up and NOT subtracting since the waveforms are added you get 120+(-120) = 0. This means that L1+ L2 if they really are out of phase then the resultant waveform would cancel itself out and hence you are left with a voltage across L1 and L2 that is 0 and NOT 240. Now if they would have been In Phase with 0° between the waveforms then the resultant would have been 240 volts. So you’re premise of them being “out of phase” has been proved wrong.
ruclips.net/video/nOSYHUxHxG8/видео.html for an alternate explanation that shows how many aspects are the confusions about 'convention', and which ones are in use.
With respect to two single phase loads (one on L1 and one and L2), the current flowing through them is 180 degrees out of phase to one another. If I have two equal loads (for instance two 60W light bulbs), there will be no current flowing in the neutral. They cancel each other out because they are 180 degrees out of phase. The two loads at that point look like one 240V load with 120V dropped across each and the current alternates back and forth through them without ever going through the neutral.
Here's a little thought experiment (or you can do it in real life if you want): I agree that no current will flow in the neutral, so let's get rid of that neutral connection; it's not doing anything. So we have L1->bulb1->bulb2->L2. Nothing changes right? Neutral was functionally absent and now it's *actually* absent. Put a mental amp clamp around the L1 wire coming out of the wall, and slide it down the wire until you get to bulb1, slide it over bulb 1 (really small bulbs) and toward bulb 2. Slide it over bulb 2 and along the L2 wire back to the wall. In your head did you see the current waveform spontaneously invert its polarity at any point? If so, when (at what point)? And why? And what would have happened if there were 3 resistors in series, rather than two?
@@charlesstaton8104 I'm sorry if it seemed that I was disagreeing with you. I do not. Just pointing out how it looks from a common reference point perspective with the current. Good video. BTW have you seen this guy's video. He goes through all of the same demos that you do, but he has an awesome setup. ruclips.net/video/nOSYHUxHxG8/видео.html
@@srtamplification yep, that's an excellent video. Better than mine, I admit. Easier to follow. After watching it I think I understand where you are coming from but if you go back to his video where he demonstrates the amp clamps on L1 and L2 and contrast it with the thought experiment i described, you might notice he's measuring current backwards on one leg compared to how he did on the other. I wish he hadn't done that because it's confusing and not consistent with the rest of his video. Current flows the same direction through both bulbs. The reason no current flows in the neutral isn't because of any cancelation of opposing currents but because the loads are balanced, which he did a great job of explaining.
But you can't just "get rid of the neutral for a "thought experiment", if you go and do the math on this subject , THATS where you get 180° phase shift. Because for voltage to HAVE current, you have to have a "neutral" , and THATS precisely what makes this a 180° shift, and what gives you 240v /120v-to-neutral in "power". @@charlesstaton8104
Excellent explanation. The fact that it's called "single phase" should be enough for people. By definition, something that is "single" has nothing to be out of phase with. Yet the misconception persists . . .
A single phase on the primary winding of a transformer CAN, in fact be split at the secondary into TWO phases. That's exactly What happens at the pole and dine every day. When you mention the word phases it is important to specify your reference point. In a residential elect circuit each side of the secondary of the pole transformer is labeled L1 & L2 with the center tap of the transformer called the Neutral. So when measuring: L1 & neutral 120v single phase L2 & neutral 120v single phase L1 & L2 240v single phase. However L1 & L2 are def out of phase when referenced to the neutral
@@rty1955 wouldn't it be L1 & L2 240 volts split phase though and not single phase. Also I'm having a hard time understanding what he is getting at in the video. Why is he saying they are not 180° out of phase?
@@anthonyesposito7 yes it IS split phase. You are taking a SINGLE phase and creating 2 phases. A phase is an angular difference of the original signal. Therefore at the secondary there are TWO phases relative to the NEUTRAL. Like I said, it depends on your point of reference. So when you say L1 & L2 IS single phase with respect with each other, however if your reference your measurement from the neutral, there are two distinct phases Helps?
@@rty1955 Yeah thanks, I actually went to Dave Gordon's channel and he explained it a little better the this video at least it made more sent to me. I completely understand now that it really is a split single phase but also L1 and L2 with reference to N are NOT 180° out of phase in that respect. I went into this video with that assumption but as Dave points out in his video is that for them to be 180° out of phase the physical windings on the transformer would have to stop at the point were the neutral is tapped and then begin to wind the other direction relative to the first half of the windings if that makes sense. Dave Gordon has a really great channel too if anyone is interested in more stuff like this.
@@anthonyesposito7 well not at all. L1 IS 180° apart from L2 with respect to the neutral. So the OUTPUT of the transformer is effectively two windings that are 180° apart. The INPUT is single phase. I say effectively because if you took 2 different transformers with the input sides wired in parallel and the output wired in series. So the output would look like C for the common of the two transformers (A&B) and T1 for the other side if winding from transformer A, and T2 for the other side of transformer B Then used a scope to look at the output phases they MAY be in phase, if you measured from C to T1 and C to T2. But, flip the T1 & C and they will be two different phases with respect to C.
According to the large majority of the comments here I am not just making people confused. I am helping them understand. Many "thank you, I finally understand" comments. Maybe I am making just you confused. Not everyone receives information the same way; if there's something you would like for me to explain in a different way, let me know.
It never made sense to me that the 2 legs of a split phase service could be 180 degrees apart, because the inductive field of a single coil cannot be made to selectively invert a part of an AC waveform with a mere center tap connection. And of course, as you point out, the resultant voltage of the opposed phases would be zero. The entire phase converter industry would have disappeared overnight as a consequence of such a discovery, yet many people continue to believe that this is the case. Great video and explanation, lavish with lots of patience and nuance, I intend to watch it at least several more times.
Sorry, but the two 120V are 180 degees out of phase. For a moment, look to a 3-phase system. If you draw a phasor diagram, the vectors all start in the centre, the neutral point. They are 120 degrees apart as the coils in the generaor are placed 120 degrees apart. Each coil producing 120Vrms in the US. The voltage between any two line conductors will be 120*sqt(3) = 120*1,73=208V. This voltage of 208V is the vector sum of the two 120V voltages. Now, we take one of the three coils out and turn the two so their phasor points directly opposite. What is the voltage from phasor to phasor: 120+120-240 V. The two voltages are 180 degrees out of phase. What if we place the two coils side by side? The two phasors will run totally in parallel, or we would say - in phase! . What is the voltage measured between the arrowhead of the two phasors? 0 volt, zero. The two 120V are now in perfect in-phase and creates a voltage of zero volt.
The fog for me disappeared the moment I thought of a center-tapped secondary transformer coil. Of course, this is exactly how power is produced on the last leg to a residence. How could the end-to-end leads of the secondary be out of phase? It's just one coil of wire! There is only one phase... The center tap just halves the voltage of the single phase result.
Exactly! That's what I've found is the most illuminating way to get the point across. If you read through the comments here, the arguments usually stop when I say that. The detractors usually won't admit it but I think that bringing this up is helping people realize what is actually going on.
@@charlesstaton8104 Another way to look at it is with a Mattel Hot Wheels track in a loop with one or two power boosters. Power boosters are like those spinning wheel baseball pitching machines. Anywho, one power booster is half the secondary coil. The full secondary coil is *both* power boosters. Things are gonna be moving along just a bit faster! Obviously, it's not a perfect analogy. But, no model is perfect. Thanks for bothering to take the time to put up the video. It's always neat to see how others see things.
Excellent presentation. Anyone with knowledge of these circuits will agree with you, but it may be bit confusing to those who are still trying to grasp it. I didn't say learning because we are all still learning. Anyhow, whenever someone challenges me on this subject I simply ask them this: How can you get two separate sine waives off one phase of power? Answer, you don't. For an explanation, look no further than the utility transformer that is wired for 120/240 volt service. You'll note on the primary side of the transformer that the H1 bushing is connected to only one high voltage phase, which will be 7200 volts phase to ground. The H2 bushing will be connected to ground/neutral. No other connections on the primary side exist. Quick note, the primary/grid side on a single phase is 7200 volts because it is a line to ground reference. On the same system, the line to line reference will be 12,480 volts. This is true on a 3 phase system because you must first find the square root of 3 (1.732) to find the answer. Simply multiplying 7200 by 1.732 you'll get 12480. What comes out of the "split phase" secondary is 120 volt to neutral from each of two legs (X1 and X3 bushings) which then go into the establishment. X2 bushing is connected to ground/neutral which then also goes into the establishment. What you'll get is a phase to phase voltage reading of 240 volts and of course 120 volt from either of the phases to neutral. But they are more accurately called legs because in truth there is only one phase coming from the utility, hence single phase. Since it is only a single phase, then the obvious outcome is there is only one sine waive. Done!
The discussions in the comments on this video have led me to the realization that I could have explained it better by leaning on the points you highlighted. I was trying to approach the topic on the same playing field that the counter-argument resides on, but it's not the right playing field and the game is rigged. The video would have been better if I stressed the fact that there is *only one sine wave* and it can't possibly be out of phase with itself. When we measure it, typically our equipment forces us to take two separate measurements of two halves of the single wave and add them together, but that doesn't mean there are two waves. One wave; we measure one half and we measure the other half. One half *appears* out of phase with the other half because typically our equipment also forces us to measure the second half "backwards" with respect to how we measure the first half. I think that explanation would be easier to digest for the newly initiated (and for the old bumps on logs who have known the "truth" of the matter since before I was born).
Vab = Va - Vb This is splitting hairs, but you don't add the sinusoidal waveforms to get the voltage between two lines. You are finding the difference (subtraction) of one sinusoidal line to neutral voltage from another sinusoidal line to neutral voltage with the opposite phase. For sinewaves there is no distinction between a sign flip and a 180° phase shift. 240 = 120 - (-120) You have a neutral wire and two hot wires. You don't have a neutral wire, a hot wire, and an "extra hot" wire in a 240V split phase setup.
@@jessstuart7495 can you articulate why in this one isolated case the voltages should be subtracted when in every other case of wave interference* the amplitudes are added? *consider sound waves, ocean waves, light waves, kinetic vibrations, AC electrical waves in every instance but the L1/L2 phase debate, etc.; every kind of wave physics knows of. Converging waves add. If they are in phase the resulting wave has greater amplitude than either of its constituents. If they are out of phase, the resulting wave is diminished. It's how noise canceling earphones work.
@@charlesstaton8104, It's because potentials are defined relative to a arbitrary reference level. Potentials are just a mathematical convenience that makes solving circuits easier. Voltage is deliberately defined so the gradient (spacial derivative) of the voltage (potential) is equal to the electric field. It is the electrical field that applies forces to charges. When you "integrate" the electric field to define the electrical potential, an arbitrary constant of integration is always there, even if you chose this constant to be zero. Electrical fields and node voltages add (superimpose), but when you are talking about the voltage across a device, this is equal to the difference in node voltages. Here's a DC example. If one side of a 1kohm resistor is connected to the positive terminal of a 9V battery, and the other side is connected to an LED with a 3V turn on voltage, and the lower side of the LED is connected to the battery's negative terminal, there will be a 6V across the resistor (Kirchhoff's Voltage Law). A multimeter will measure voltages in RMS, which is always a positive quantity. It appears like the hot to hot RMS voltage is the sum of the hot to neutral voltages, but this isn't really the correct way to think about potentials. Again, I am splitting hairs here.
@@jessstuart7495 the DC example I like to use, is two 12V batteries in series. With a string of any number of batteries where the voltages add, like on a golf cart for example, almost anyone would find it intuitive to lift both DMM probes off the batteries, measuring from + to - of each battery. If you had two in series you could look that them and tell right away without any measurements that they have like polarity. But if you couldn't see the markings, a quick check from the negative terminal of the first to the positive terminal of the second, would tell you that they have like polarity if 24V is measured. But if instead you *_arbitrarily_* (as you mentioned) decide to pick the node between the two batteries as your reference, permanently weld your black DMM probe to that junction so that no measurements can be taken with reference to any node but that one, you would measure -12V to the first battery and +12V to the second. Since this is a very basic situation and you *_know_* that the two batteries are actually, physically, connected in series with like polarity, then you *_know_* that one of your *_measurements_* is being taken with opposite polarity. Since you *_know_* this, rather than correcting the sign of your backwards measurement and adding the voltages as one should, some may find it more intuitive to change the sign of operation rather than the sign of the value and say +12V-(-12V)=24V. That's just fine with me, if your numbers are just for your own reference or if everyone you're sharing this data with is on the same page. What I have a problem with is when this ends up getting taught and regurgitated by the masses who *_aren't_* on the same page and *_they actually think_* that one of those batteries has opposite polarity from the other one, and for reasons they can't articulate, we subtract in this case instead of adding. Since you can articulate the reason, I would like to make you aware that not everyone is on the same page. The way that you're wording things, the established way of wording things, is misleading. There is a fundamental misunderstanding rife in the community as a result. If you think I am splitting hairs, just ask around. I think you will be surprised at how many people actually misunderstand this.
This video provides one of the best explanation of the concepts. Two voltages of equal magnitude that have the same polarity(0° in phase) and placed in series sums. Ex: 120v + 120 = 240! However, if one the voltage is 180° out of phase(reversed polarity) their voltages still sums! Ex: 120 + (-120) = 0 But it's impossible for a spilt-240 v service to be a 0v line-to-line and still give 120v on line 1- neutral; & line2-neutral! 0° to 180° is a straight line which has no angle! If two sources are 120v each and are not in phase the sum of their voltage is less the 240!
Kirchhoff's Laws might help out here: 1) The sum of all currents entering and leaving a junction add up to Zero 2) The sum of potential drops around a closed circuit add up to Zero
Your presentation has initiated some great unrelated thoughts: If we imagine a voltage supply transformer of 240v feeding two resistors of 4ohm and 2ohm connected in series then the current flowing in the circuit is 240÷6=40amp Now if we centre tap the transformer and create a neutral path between the resistors and feed each resistor with 120V we will have two separate closed loop circuits. The current flows will be as follows: 120÷4=30amps 120÷2=60amps At the node point of the two resistors and the neutral we will have 60amps flowing into it from the 2ohm resistor circuit and 30 amps flowing away from it to the 4ohm resistor circuit. The other 30amps will flow down the neutral to the centre tap of the transformer. At the centre tap of the transformer we will have two currents flowing in, each of 30amps, one from the closed loop of the 4ohm resistor and the other from the neutral. These currents will add to give 60amps which will then flow in the closed loop of the 2ohm resistor circuit. I am not sure how relevant this is to the current discussion and hopefully my analysis is correct.
When you hook the positive of One battery to the negative of the other battery why did it not short out is that just cuz you didn't have the two batteries in the same circuit
And we’re back to ground, again. The circuit includes the ground and the axis is conventionally placed on ground, so everyone sees the same thing, when looking at waveforms. If you’re going to do something unconventional, your results are going to look different from everyone else’s. Ultimately, current is electron flow and will always try to flow from more negatively charged places towards less negatively charged places. Over the years, the way we reason that out has changed and will doubtless do so again, but for now, the convention is to plot graphs relative to zero and zero is whichever leg is grounded. That’s just the way it is.
Thank you for connecting the oscilloscope with both ground references together, at ground, on a dual trace scope. This proves beyond the shadow of a doubt that there are TWO 120VAC phases, and they are 180 deg out pf phase. We measure 240VAC because of the absolute voltage compared to ground, between the 2 hot legs. The title of your video is deceiving at best, and dangerous at worst. It's time to adjust your understanding, rather than trying to change physics.
Nope. Single phase is *SINGLE* phase. Not sure why you would say otherwise. Take an isolation transformer with no center tap; current is flowing the same direction through, and voltage is induced with the same polarity across, each and every turn of that winding. Agree? Now identify the very center turn of transformer, scratch the enamel off it, and solder a wire on. Did you magically invert the polarity of half of the winding? No you did not. Connect that center wire to an earth rod and call it "neutral." NOW did you magically invert half the winding? No you did not. You just created a split phase transformer exactly the same as pole transformer and the two halves of it are *NOT* out phase with each other or inverted with respect to each other. Not sure why the truth is so "dangerous" in your opinion.
@@charlesstaton8104 "...magically invert the polarity..."? No, it's not magic. That's simply the way it IS, when we measure in reference to the center tap. If we split the winding at that point, THEN we have two coils in the same phase. It's telling, that all the demonstrations you did prove that point, and yet you insist on understanding it incorrectly. It's much simpler than all the man-splaining contortions. Get your money back from whomever taught you incorrectly.
@@stirlingschmidt6325 so adding a center tap *DOES* invert the polarity one half of the transformer, but just not magically? Got it. Great explanation, really. Thanks. Just one question though, if "magically" doesn't describe the phenomenon, what word does? Spontaneously? I noticed you started using the term "with reference to neutral" which I am a big fan of forcing people to use, since it is the first step toward realizing that they are measuring two halves of a series string of voltage sources (each turn of the secondary around the core can be considered a separate series source) from the center outward, so one half is measured with opposite polarity from the other, thereby making one half *appear* inverted from the other.
Hey man, nice video and great discussion. Not trying to change your mind, only offer a different perspective and way to conceptualize this. As you probably know in AC circuits there is no positive voltage or negative voltage. Only electrons flowing to and from the source due to transition of north to south magnetic poles in the generating equipment. Much like two cars traveling the same speed in exactly opposite directions the relative speed to each other is double not zero. If you were to observe one of these cars and you were standing still their speed would 1/2 their relative speed. For a US split phase residential service the common reference point is the center tap of the step down transformer. much like the mid point of a North to South magnetic field where the magnetic field is parallel to the coil (eg 0 flux eg 0 volts eg neutral) center tapping the secondary creates a new reference neutral point. Voltages to the left and right from this new neutral increase proportionally in opposing poles (North and South) I think where you’re confusing people is intermingling direct current with AC circuits. There is no positive or negative in AC. Only voltage differential caused by phase differentials which don’t cancel out. When you’re measuring a peak wave to another peak wave below your reference point the peak wave below the reference point is not negative. Think of the Peaks as a North Pole peak and a South Pole peak. And we all know the max potential force is measured North to South. So yes, split phase 120V services are exactly 180 degrees out of phase. If they were anything else they would not be exactly double their additive values. For example if they were 120 degrees out of phase their additive value would be 208V. Eg a 3 wire network service. Hope this helps, look forward to any discussions.
"in AC circuits there is no positive voltage or negative voltage." - yea there is. Voltage always has a polarity. In 60Hz mains AC, the polarity changes 60 times per second. "Only electrons flowing to and from the source due to transition of north to south magnetic poles in the generating equipment." - when electrons flow (current) through a resistance they create a voltage, and that voltage has polarity. "Much like two cars traveling the same speed in exactly opposite directions the relative speed to each other is double not zero. If you were to observe one of these cars and you were standing still their speed would 1/2 their relative speed." - for center-tapped *single phase* electrical supply, the more accurate car analogy is that you the observer are standing in the exact center of a 1/4 mile drag strip as a *single car* races from one end to the other, turns around, and races back, turns around, and so forth. The parameter of interest isn't that car's speed, but its *distance* from you. That car is going a full 1/4 mile each time it turns around, but Since you're in the center of the track, it *appears* to only go half that distance. So what is this car 180 degrees out of phase with? "For a US split phase residential service the common reference point is the center tap of the step down transformer. much like the mid point of a North to South magnetic field where the magnetic field is parallel to the coil (eg 0 flux eg 0 volts eg neutral) center tapping the secondary creates a new reference neutral point. Voltages to the left and right from this new neutral increase proportionally in opposing poles (North and South)" - continuing the single phase/single car analogy, since you're in the center you think of yourself as the starting line, as the "zero." Since you're "zero," we say that when the car is on your left its distance (from you) is negative and when it's on your right its distance (from you) is positive. But your position is arbitrary. You could have chosen to stand anywhere on the track. You could have chosen to stand at the end, where the driver of the car would probably consider the "zero" point. Then its distance would go up to 1/4 and down to zero and back up to 1/4 mile. Your choice to stand in the middle does not cause a second car to materialize on the track driving ever in the opposite direction of the first car. There is only one car. Only one phase. Only one wave. That car/wave/phase *cannot* be "180 degrees out of phase" with *itself.* "I think where you’re confusing people is intermingling direct current with AC circuits." -am I confusing people? From all the other comments it seems I am not. I like to use DC analogies as far as I can take them because batteries are much more intuitive for most people, and in this video I went about to the limit of where you can apply DC analogies. Any more in-depth and I would have had to abandon them. "yes, split phase 120V services are exactly 180 degrees out of phase." - I'm sorry, but they are *not*. "If they were anything else they would not be exactly double their additive values. For example if they were 120 degrees out of phase their additive value would be 208V." - if they were 180 degrees out of phase their additive value would be *zero* as I repeatedly demonstrated, not double. You get a doubling when two waves are exactly *in* phase. But in the case of center-tapped single phase, there is only a single wave and instead of measuring it directly, typically you're measuring one half of it plus the other half of it. Since you're measuring these two halves with one set of probes backwards, the second half *appears* reversed. "Hope this helps, look forward to any discussions." - I hope this is eye opening as well.
Didn't get this in my teens and twenties, and still don't get it in my sixties, even after retiring from thirty five years in aviation. Thanks, anyway.
Damn, I remember browsing youtube many years ago and being confused about - how the hell just adding center tap can invert phase?! And almost every popular youtuber and even pro electricians couldn't explain it lol. Turns out it is just a measurement problem.
DC does not have a phase it could have a frequency if it's pulsating DC current. All I can say is homie needs to lay off the Red Bulls. I do understand his point but trying to explain this to someone that does not have a clue would be like lost
I did the same experiment but used a multi tap transformer used for HVAC. This is perfect to get people to understand how split phase truly works, and just how important your reference is.
Great video. Have you heard about "balanced AC power"? This is a special installation for recording studios and other facilities where stray ground current can be an issue. You have a transformer with a 120 volt center tapped secondary. The center tap is grounded and your equipment connects across the two 60 volt legs of the transformer, which as this video illustrates are in fact single phase 120 volts. This configuration reduces stray ground current. Article 640.9(A) of the NEC covers this type of system. Labeling and color codes are strictly spelled out as the so called "neutral" side of a receptacle is now 60 volts to ground at full breaker ampacity. Double pole tied circuit breakers are also mandatory and a dedicated breaker panel must be used. In essence, a balanced 120 volt power system is exactly the same configuration as standard split phase residential in the USA but it's 120/60/60 versus 240/120/120 to the grounded center tap.
You could get yourself differential probes for your Tek (BTW, my Tek also had a cap fizz on me, must be a Tek thing. I use my Rigols now), or any other scope I imagine. I use the simple mod that you mentioned to keep from vaporizing my ground lead, and with the plastic-cased scopes these days it's not as risky as it once was.
I gave the Tek to someone on the internet. A newbie who wanted to try fixing it for experience, and was hopeful to get a free scope for the effort. Not sure if they ever got it working.
@@charlesstaton8104 That's the right thing to do in my opinion. I'll eventually find someone in need of a scope (and it still works even with the blown cap).
@Robert Swaine Old analog scopes aren't really worth the trouble, they are useful for analog-ly things like power supplies. I'm very fond of the Rigol products, not only are they very affordable, but delightfully hackable (hint: don't buy the upscale model without checking what you can do with the base model). And then there's the FNIRSi ADS1014D scope/frequency generator & counter for $185. Runs off of USB power or the adapter. It's a cheap, fairly capable scope. Good for 400 Volts - until it isn't. :)
Split phase is defined as a center tapped transformer L1 to L2 is 240v RMS. The center tap is defined as neutral and is also tied to ground at one point. We all realize it is 340v peak to peak. For apartment work, split phase is not two legs of the three phase system.
Yes, and no. A 3-phase system has 3 coils 120 degrees apart. Each coil producing 120Vrms and the vector sum between two coils is 208Vrms. Now let us rework this generator a little: we take one coil out and open the angle between the two from 120 to 180 degrees. What is now the vector sum of the two coil voltages? It happens to be 240V in a two-phase system with the two voltages 180 degrees apart.
In a split-phase (i.e. single-phase three-wire) system, the L1-N voltage lags (or leads) the L2-N voltage by 180 degrees, simply because you’re measuring both voltages with respect to the center tap. If you measure L1-N and N-L2, then you get both are in phase, as expected. This is what happens when you place two AA batteries in series. - 3:20 Incorrect, the three windings are not 120 mechanical degrees (120 degrees in space) apart, they’re much, much closer to reduce harmonics.
In the interest of simplicity my explanation assumed a 2-pole generator hence the comment about 120 mechanical degrees. But most generators are not 2-pole, so yes the windings for most generators will be closer to each other than 120 degrees.
I don't understand you. For the single phase supply we are talking 180° out if phase between each line and neutral. You are going into semantics. Don't mislead viewers. Everything is relative.
*everything* isn't relative. *_Measurements_* are relative, but the polarity of induced voltage and direction of current flow are NOT relative, and are the *same* in both halves of the transformer. The way we take Measurements makes one half *appear* to have inverse polarity but in reality it is not. This video is about people using absolute terms to describe their relative Measurements. If you say "L1 *IS* 180 degrees out of phase with L2," then *YOU* are the one misleading people. It is only accurate to say "L1 *_APPEARS_*_ 180 degrees out of phase with L2 _*_when both are measured with respect to neutral."_* this is more than a semantic disagreement.
To the morons who keep insisting that the standard 120/240 volt Edison system is split phase. What would you call my 8,16,24 volt output on my chime transformer ? Maybe not split phase maybe 3 phase. Nope . Nice Fluke piece of test equipment. Just wish they could show where in an quality engineer book that ever says the 3 wire 120/240 single phase system can magically become split phase.Only split phase that I ever read about or worked on was on some AC motors feed from two wire as single phase and had either a capacitor in series with a start winding and some without a capacitor but a start winding.that was out of phase thus giving these motors the term split phase motors.
I understand and agree with the premise of your argument. Adding a tap to a transformer does not add a phase (an additional EM wave). I've seen transformers with as many as 12 outputs on the secondary. That was not a 12 phase transformer, it was a single phase transformer with 12 outputs. That said, I think your understanding of the usage of "split" in this context is different than everyone else's. On that transformer with 12 outputs, the secondary is *split* 11 times (and if you unwind it you'll find that it literally is *split* as the term implies). The usage of the term "split phase" power for residential mains is very much preferred in my book, considering the alternative is *two phase* which is borderline blasphemy. If you want to find the term "split phase" in an EE textbook, check out this citation from the Wikipedia page on split phase (I haven't read the book myself): Terrell Croft and Wilford Summers (ed), American Electricians' Handbook, Eleventh Edition, McGraw Hill, New York (1987) ISBN 0-07-013932-6, chapter 3, pages 3-10, 3-14 to 3-22. The "split phase" i believe you referring to with regard to motors is the PSC (permanent split capacitor) motor. And it's a good thing you brought up motors, because the capacitors in single phase motors (as opposed to taps in transformers) *actually do* create new phases, with measurable phase angle difference from the original.
You are creating unnecessary confusion. Apparently your o'scope has floating probes inputs that can be connected anywhere. You are connected the probe "ground" lead to hot wires. Most scopes would end up with fired probes if you did that. Normally all your probe ground leads have to connect to a grounded or neutral reference point. When connected this way you will obviously see two waveforms of opposite polarity - i.e. 180 deg out of phase. To get the total voltage between two wires, you subtract one from the other. So it's 120 volts minus negative 120 volts. which equals 240 volts. This is a valid understanding. No need to confuse people by claiming it's not true. The same is true if you had a DC power supply with a +12 volt output and a -12 volt output, both referenced to a "common" terminal. You wouldn't tell people it's not really a -12 volt terminal. That's the way most people would understand it. The voltage between the two terminals is +12 volts minus -12 volts. You can still think of it as two 12 volt supplies in series if you want. But don't say the other explanation is wrong.
I've seen this +120V minus (-120V) argument before and I don't understand where it comes from. Why are we subtracting? Shouldn't we be adding? In what other scenarios do you subtract? And how do you know when you're in a subtracting scenario? "You can think of it as two supplies in series if you want" ... is there any more valid way to think of it? That's exactly what it is. You brought up dual 12VDC supplies and I would like to further that analogy. Let's say your DC supplies are batteries, and there isn't two of them, there's six. It's a series string, all same polarity, let's say for a high voltage golf cart. But we don't know that yet. We look at it and see that there are 6 batteries, each marked 12V, and when we measure from one end to the other end with a DMM we get 72V. That right there tells you the entire circuit, even if you can't see how the wires are routed. There is only one configuration of 12V batteries which yields that result: 6 batteries, all in series, all connected with the same polarity. If one of them had opposite polarity from the rest, you would measure 48V, as the voltage from two of the batteries would cancel out. If two batteries had reversed polarity you would measure 24V. If three batteries were inverted, the entire pack would cancel out and you would read 0V. From the 72V measurement we know that the batteries can't be anything other than all in series, all same polarity. That would be true whether you were measuring from either end, or center to either end, whatever. This would be true too, if there were only two batteries. And if they were 120V. And if they were AC instead of DC. And if they were transformer outputs instead of batteries. Now I circle back to answer my original questions. We know that we are in a subtracting scenario when we know that we are *measuring* one of the series sources with opposite polarity from the other(s). That informed decision to invert the mathematical operation is to compensate for the known inversion of the measurement. That's all fine and good if it's an informed decision and a known inversion. But in many (dare I say most?) cases, it isn't either of those - it's rote regurgitation of something they were told, and think they understand, but don't. You obviously get it but my experiences in discussing this with others indicate that most don't. They think L1 and L2 are literally inverted with respect to each other. These folks can talk at length on this topic, saying all the right things "conventional model" things and you'd never know that they actually have a completely different (and flawed) understanding from the one that you and I do. You only discover it by digging deeper, where you find that many think current flows opposite directions through the loads on L1 and L2. And further misunderstanding builds from there. I don't disagree with anything you said, apart from the bit about "causing unnecessary confusion." I think (and other comments seem to confirm) that seeing things demonstrated this way is eye opening for a lot of people. The conventional model and its double negatives are confusing. Lots of people find this one less so. I believe that people can be trusted with truths that challenge convention and the world won't descend into chaos. Otherwise this video wouldn't exist.
Apologies, but you know enough to be dangerous. 120V 3 phase, phase to ground or phase to phase is not the same as a household 120V split phase. Being amazed that different measurements give different results -> just do the math first... it's rather simple. Coming from a power electronics engineer that learned the actual facts about 40 yrs ago - facts don't change.
Apologies, but you watched just enough of the video to think you knew what it was about before commenting on how educated you are, how educated I'm not, and take shots at me over nothing specific. You contributed nothing of substance. Now you have the opportunity to do better. If you'd like to discuss some of these facts you learned 40 years ago, please feel free to pick something from the video that you think I got wrong, and set the record straight.
But once again, the important thing is the ground. A load applied across L1 and ground, only, will experience the opposite polarity, compared to the same load applied across L2 and ground, only. This will be so, at all points in time, other than at crossover. Therefore, the current in the load will flow the opposite direction, in the load! If you think about it, it ALWAYs flows in opposite directions in L1 and L2, because at any point in time, if L1 is positive going, then L2 is negative going, so current will be going towards the source on one while coming from it on the other. What changes, with split phase, is where the current goes. When you have the center tap, regardless of ground tie, some of the current goes through that, meaning the two ends are no longer necessarily balanced and are instead determined by the loads applied. In an ideal world, for maximum efficiency, you should balance the loads perfectly, making the center tap current zero, but this isn’t practical and I suspect that’s partly why the practice is not done on this side of the Atlantic. Over here we don’t like generating power that doesn’t get used, so we use the full wave 240v. (Actually standardised 230v, nowadays) But it’s really important that people understand that, while accidentally coming in contact with either L1, or L2 while standing barefoot will probably not be a fatal event, both at the same time most likely will, especially if wearing insulated safety footwear. Videos like yours blur that, for regular folk.
My video doesn't blur that, it refutes it. Current does *not* flow opposite directions through the loads on L1 and L2. I made a separate video to demonstrate that. It is short and sweet unlike this video: ruclips.net/video/3PHjZOdqs1U/видео.html Imagine nothing is connected to your breaker panel. You install one two-pole breaker. To that breaker you connect two 100ohm resistive loads in series across the 240V. Does current flow opposite directions through the two resistors? It shouldn't. It can't. Current can't flow two two directions at the same time in the same series circuit. Now at the node between the two resistors you make a connection to neutral. Does anything change? It shouldn't. No current should flow in the neutral since the loads are balanced. And adding the neutral connection does not (can not possibly) cause any polarity inversion or phase shift. The current flows the *same* direction through the loads on L1 and the loads on L2. Current flows the *same* direction through both halves of secondary of the pole transformer, and voltage is induced across both halves of the secondary with the *same* polarity. The only reason why it appears opposite polarity/180 degrees out of phase on the scope is because the scope measures one half of the secondary with opposite polarity as the other half. It is an *apparent* inversion, not a real one. And I think it is important that the less experienced folk learn this *fact* early on so they don't develop lifelong fundamental misunderstanding.
You are so confused and wrong. Yes, you measure voltages with respect to a reference. When the center tap is tied to ground as the reference, one of the "split phases" is -120V wrt ground, and the other phase is +120V wrt ground. So half of the coil of the secondary is below ground, and the other half of the coil is above ground. And what's the total difference between the two outer legs? 240V. But that's not 240V wrt ground, that's 240V wrt to the one end of the coil of the transformer. If you tie the center tap of the transformer to ground and call that the reference, then one side is +120V and the other side is -120V with respect to ground. But if you ignore the center tap and tie one end of the coil to ground and call that the reference, then the other end of the coil will go between +240V and -240V. The only one that's "confused about ground referenced measurements" is you!
I agree with everything you said here (except the part about me confused about ground referenced measurements) and I'm not sure how I managed not to convey any of that (to you) at least once in the video. Thank you for reiterating the content of my own video to me in a condescending didactic tone.
What a waste of time! The first thing you did was to correctly produce two sine waves 180 degrees out of phase. The rest was useless. You must be one of those PITA people at parties.
Okay I grant you that, but it’s not a practical point. Truly isolated supplies are rare and vulnerable humans are almost always connected to ground. Therefore, using ground as the common reference remains the safest option and treating the “hot” wires as separate phases is a valid, safe premise
One thing I've learned in the 2 years since I posted this video is that the word "phase" is dangerous. It means different things to different people, and it is rarely obvious what definition a person subscribes to as you discuss the matter. It is possible (common, even) to go through several pages of discussion with both sides thinking they're addressing apples with apples when in fact one side is talking oranges. I don't know definition you subscribe to, but per the one I do, I can't agree that single phase power is two phases. I do agree however that isolated supplies are rare, isolated scopes even more rare, and ground is the safest reference point for anyone, especially those in the early stages of learning. I didn't mean to encourage non-ground-referenced voltage measurements, but only to demonstrate what they look like since I'm in a position to do so. If one never steps outside the mental realm of circuit analysis then my experiment probably seems of little to no (or negative) value. But for someone who spends most of their time in the measurement realm (the real world), the answers from the circuit analysis realm don't hold up. I hope my video illustrates why.
you cannot just choose your reference points willy nilly my friend. They are 180 degrees out of Phase when measured from the same point of reference. This is the same for the actual flow of the current. If they are flowing with respect to the same reference (the neutral) then they are in fact out of Phase so spin it how ever you want but the apples are still apples!!! You should get a job in marketing and leave expensive industrial control alone!
Yes, you *can* choose your references willy nilly. Voltage is a differential measurement just like distance. It has a "point A" and a "point B" and as long as you state those two points it's a valid measurement. You obviously understand that as you said "when measured from the same reference point of reference" so I find your next statement puzzling: "This is the same for the actual flow of current" - you honestly think current is flowing two directions simultaneously within the same coil of the transformer secondary? Please explain.
The measurement of phase should be taken from a common point. By reversing your reference on one of the phases, of course you can show them as being in phase. If you have two lines "in phase" and of the same electrical potential to their reference point, you will measure zero potential difference between them and you will be able to connect them together to increase the current supplied. If you have two lines which are 180 degrees out of phase according to their common reference point, you will measure double the potential difference between them and connecting them together would create a high current short circuit. Your hypothesis is wrong!
The measurement of *phase* should be taken between two separate *phases.* Single phase is *SINGLE* phase. No valid measurement of phase shift is possible. Take an isolation transformer with no center tap; current is flowing the same direction through, and voltage is induced with the same polarity across, each and every turn of that winding. Agree? Now identify the very center turn of transformer, scratch the enamel off it, and solder a wire on. Did you magically invert the polarity of half of the winding? No you did not. Connect that center wire to an earth rod and call it "neutral." NOW did you magically invert half the winding? No you did not. You just created a split phase transformer exactly the same as pole transformer and the two halves of it are *NOT* inverted with respect to each other, nor are they out of phase. They can't be out of phase because *they are the same phase.* On the scope you're just looking at two halves of the same wave and one half *appears* inverted from the other half because it's being measured with inverse polarity from the other half.
False. As I demonstrated repeatedly, if they were 180 degrees out of phase they would add to zero. Just like there would be 0V between (+) and (+) on two batteries that are connected from (-) to (-). The only way you get two 12V batteries to add up to 24V is if you connect them [(-)...(+)][(-)...(+)]. That is to say, *same* polarity, or in the terms some people use, *same* phase. Same goes for AC.
Agreed. But you try telling some people that and and you'll realize the concept behind the word "phase" is not the same for everyone. It seems that people who go to college for Electronics Engineering, come away with an understanding of phase that is purely mathematical and they have no qualms about discussing "both phases" of that single phase source, and they back up their arguments with phasor trig. You don't even need need to break out the higher maths though. If you measure the length of a stick from the center outwards, it will require two separate measurements in opposite directions. It doesn't mean there are two sticks with opposite lengths, even if mathematical proofs can be interpreted that way.
*Phase* measurements are referenced to *another phase* . This is *single* phase power. There is no such thing as a valid phase measurement of single phase, unless you're comparing current to voltage in the same phase. If you have a transformer with no center tap, is the voltage across the primary out of phase with itself? No. If you scratch the enamel off the center winding does that change? No. If you solder a wire onto that center winding, does that change? No. If you connect that wire to earth and call it "neutral" does that change? No. If you start taking all your measurements with reference to the new neutral, does that change? No. It will look that way on your scope, but your decision to call it neutral does not cause any magical inversion or phase shift. When you're looking at L1 and L2 on a scope, you're looking at two halves of the *same wave* and that wave *can not* be out of phase with *itself.* It only appears that way because you're measuring one half of the wave with opposite probe polarity from the way you measuring the other half. What I proved was that if you change your probe polarity to match the transformer's polarity, you see what is actually going on. I lied about nothing.
Great video , thanks! I also thought that L1 and L2 hot wires in an electrical panel are 180 degrees out of phase with each other. You cleared it all up nicely! But can you please explain how is it that when you have a balanced load on L1 and L2, meaning that L1 and L2 have the same amperage flowing through them, lets say 5 amps respectively, the current through the Neutral line is zero? What causes this cancellation of current flowing through the Neutral line? Why does not the Neutral line show 10 amps? Would this suggest that while the voltages between L1 and L2 are in phase the current between the 2 lines are out of phase? Which somehow does not make sense.
imagine you have two 9 volt batteries connect in seris + - + - and across the two, you get 18v. Now you hook two 9v light bulbs in series. The voltage drop across the two loads has to equal the supply of 18v, so across the first load you get a drop of 9v, at this point, you would have 0 volts between the spot between the two light bulbs and the point between the two 9v batteries. So, now we have this wire connected between the two light bulbs connected also between the two batteries and that's our "neutral". Now disconnect one bulb; what happens? The other bulb remains on, and the "neutral" forms the circuit for a single battery and bulb.
The fact that L1 L2 are 180 deg out of phase is what allows the cancellation of current in the neutral, this video is misleading and the conclusions are wrong.
As a retired electrical engineer I just had to say something,That's because this guy is just adding confusion to the hole thing by saying that it's not 180 degrees out of phase, because it is 180 degrees out of phase. It's a matter of where it's referenced too, single phase distribution transformers have two 120 volt windings that are normally connected in series, which forms a 240 volt winding, center tapped. Here in north America the center tapp is always connected to ground thus farming what everyone refers to as split phase, which from the point of view of the neutral or current carrying ground, and the actual Earth ground non-current carrying ground. The two 120 volt leggs are most definitely 180 degrees out of phase, for if they weren't, as he demonstrated in his confusing video there would be zero volts between the two hot legs, and because there 180 degrees out of phase is why when there's an equal load on each leg, the neutral is at zero current, and if the loads are not equal, then only the deference current appears on the neutral, because it's actually two loads in series across a 240 volt winding, which is why you never want to lift a neutral on a live panel because if you have a large deference between the two loads let's say in terms of resistance and ohms, one load has a resistance of 10 ohm's and the other is only 1 ohm, the 10 ohm load will have 9 times as much voltage across it as the 1 ohm load or 216 volts while the 1 ohm load only has 24 volts across it, how ever if both loads are equal in resistance and you lift or disconnect the neutral absolutely nothing happens. I hope this clears up some of the confusion!
@@Brokendiode This guy is showing you that your premise is incorrect but you will not accept the truth. Let’s think of one branch circuit. It is a two pole 15 amp breaker so you would have 240 volts from L1 to L2. Correct? So, let’s take a #14 black from L1 to a 1200watt quarts lamp. And from the other side of the lamp white to the neutral bar. Now the lamp will work at 120 volts and be using 10 amperes. Correct? Ok, now let’s take another 1200 watt lamp and connect it to the same point on the white and run a red #14 back to the breaker on L2. Now you have another 120 volt lamp and 10 amps. Correct? If you agree so far great. Now turn of the breaker, cut the white wire next to the two lamps and turn the power back on. What happens? Will either lamp light up? Will they both burn out because you now have 240 volts going out. There is no 120 volts coming out of the breaker because no neutral. The answer is they will both work perfectly because the two 1200 watt lamps are in series on 240 volts.
Good video bro, I think the term phase has to do with how the voltage rise & it's direction on each line really. So L1 & L2 are hot L3 low side that is shared, center tapped. Good point you make thou, it's like ,2 generators in one, two different 120 volts supply line.
When they are in phase they add! Its not split phase its a multi transformer. This has confused me in learning the difference between US 240 and EU 230. I feel like people act like they are different but they aren't its just one sine wave, its not adding two waves together. 240 is simply two legs of a 3pole multi step down transformer where the middle between half the windings is tied to ground instead of one of the ends thats why its split voltage its not truly split phase and I feel that term needs to die off. I wonder if that was from a lack of understanding in the past. I finally understand how US 240 actually works vs what everyone seems to say. Secondly when everyone talks about getting the neutral in a split voltage transformer why they act like you couldn't just neutral one of the other legs. From my understanding of a transformer it doesn't actually have a neutral in the first place its a leg on a transformer. If neutral wasn't tied to ground at all it would just be a phase. The only reason its not "live" is cause of how its all wired to ground and electricity takes the path of least resistance. Or is there something more Im not seeing?
Sorry Pete I don't think I can properly answer your questions; I'm not very familiar with EU distribution systems. It's my understanding that your 230V single phase is actually one phase of 400V 3-phase system, which different than what we have. As far as I know you don't have any split phase in the EU. but I am probably wrong.
@@charlesstaton8104 Correct EU doesn’t use split. Delta to substation then star to home. 230/400 50hz. Heavy appliances use 400 like ovens but in most cases can be wired as 230 as the induction burners use the 230 side. They have a few options for how to wire and are wired directly to the panel in Sweden, Germany, and many others not sure all. Rural parts of Norway use delta to home and simply ground one of the phases to create a neutral. In some cases this possibly leaves some people with ungrounded neutral but pretty much everything that plugs in has to use a two pole “though cheap stuff isn’t always setup right, like some lamp switches” as there is no polarisation like the US, UK and AU. The Schuko plug allows you to plug in grounded plugs in either direction. And most plugs now have shutters in them like the UK ones. Granted Norway might have updated the older parts of the grid by now to the modern standard. This 400v 3phase to home does allow 3phase ev chargers to be installed into the home which is pretty cool. France however while using a polarised plug does not have a standard for wiring “so I’ve heard” so one still needs the two pole switches. Anyway thank you for the response. Edit: also the lines along the street are house voltage which does make it easier to steal electricity as one does not need a bucket to convert to house voltage. Sorry this was long I love learning / discussing the differences in these things.
You suggest that the term “split phase” is misleading and should be dropped, but we need a term for the North American system. I think “split phase” is convenient and appropriate. It is used for a transformer which takes a single phase from the 3-phase distribution network and produces two outputs of identical voltage but opposite polarity. What would you call it without using too many syllables? “Path of least resistance” is incorrect. Electricity takes all paths, but more current flows in paths with lower resistance.
@@GH-oi2jf Well good points and thats true. After reconsideration I think the common interpretation of split phase is why I felt it was misleading. Since it is a split phase that actually does make complete sense. It's just that everything I read made it come off as misleading but I see my error in reason now. Regardless no mater my opinions anyway the standards are set. That isn't about to change anytime soon.
Ya those isolated oscopes look pretty neat. You do make a good point about test equipment polarity vs actually equipment polarity. It's important so you can accurate know how things are looking like. However it's still technically 180 degrees out of phase from the point of view of the center tap neutral of the transformer.
"From the point of view of the center tap neutral" is fine by me. If you're saying that then obviously you understand the concepts and you're taking care to use precise language. What I have a problem with is people saying they *are* out of phase without any stipulation about measurement reference and when you try to correct them with "they only *appear* out of phase because you're using the center tap as a reference" they double down on "no, they literally *ARE* out of phase." That's the notion this video was made to address.
@@charlesstaton8104 Yes, they are out of phase with respect to ground, because that's how the transformer has been set up - with the center tap tied to ground. When you measure across both "legs", you get 240V (with respect to the other leg), but yet you still only have +/-120V wrt ground. So you have 240V potential between both legs, but each leg is only at most 120V away from ground, but they are away from ground in the opposite direction at any given time - hence they are "out of phase" with eachother when compared to ground. So how does this not mean that 120V split phase is 180 degrees opposite phase on both legs? The fallacy you've committed here is you want to take the reference point as important when you talk about amplitude, but not the reference point as important when discussing phase. You have to use the same reference point in talking about both values, or you end up in the logical fallacy that you've fallen into.
@@gorak9000 the measurement that oscilloscopes take is (amplitude @ time). When I refer to being out of phase, I'm referring to the measurement taken by the oscilloscope, which as I just stated, is amplitude @ time. I didn't realize I was expected to call out both elements of the oscilloscope measurement and discuss them individually each time I say "phase." I thought it would be sufficient to just point at the scope. My bad. I will try to do better.
Correct. This is why you are allowed to use only one neutral if making two 120v circuits from 240v without up sizing the neutral. These are called Multi Wire Branch Circuits in the electrical trade. A common residential mistake (like my house was initially wired) is putting both circuits on a tandem circuit breaker not realizing a standard breaker slot is only one phase. That could be a fire hazard if the combined current exceeds the neutral wire capacity. IIRC, the 2014 NEC now requires circuit breaker handle ties on a MWBC. This was because if only one side is turned off, neutral current can still flow where it is not expected creating a maintenance shock hazard.
Excellent demo! The key is to stop thinking of 240V from this type of system as two combined phases, because it's a single phase. 120V is just using half the coil length, hence "split phase". Two halves of the same winding can't be out-of-phase with each other - it can't be out-of-phase with itself. It would also help if people stopped calling L1 and L2 "phases". They are merely bars, and a bar or contact point by itself doesn't have a phase, only a signal/circuit has a phase.
It’s conceptual. If you look at L1 and L2 simultaneously with respect to the center tap, you see two patterns 180° out of phase. This was illustrated early in the demonstration. The entire secondary is single phase, and cannot be out of phase with itself, but when you look at one-half of the secondary upside-down, it is reversed relative to the other half, or, equivalently, out of phase.
@@GH-oi2jf - Exactly, "upside-down" being the stipulation. For years, that goofy convention has confused the hell out of people when they try to reconcile it with the what they know about out-of-phase waveforms cancelling out. It would be much simpler and clearer to first teach that the L1-N circuit and the N-L2 circuit are IN-phase, so it gets visualized correctly and jives with prior learning in trig and physics.
@@pterafirma - I’ve had trig and physics and I have two engineering degrees. In my opinion, it is sometimes useful and can help understanding to view L1 and L2 as being two opposing phases, particularly to someone who is familiar with the European 3-phase systems, but noy the North American system. It is just a matter of point of view. The mathematics are equivalent. This is much ado about nothing, in my opinion.
I watched about 1 minute of Clough42s latest video and got irritated at also hearing the misconceptualized 180 degree out of phase explanation for about the 5 millionth time as well. I appreciated the sentiment and tone in your forum post linking to your video, and I share it. Misery loves company, I'm just glad you're here with me. 😆
The struggle is real my friend. Curious, which forum are you referring to? It took dozens of battles on various forums over a span of a decade to finally spur me into making this video. I believe the one that sent me over the edge was on TractorByNet.
I'm subscribed to his Channel and I love his content but I couldn't help myself. I posted this on his video (copy/pasted): Center-tapped single phase residential mains does *not* have two legs 180 degrees out of phase from each other. It is a *single phase* supply so there is only a *single* wave. Since there is a center tap, that allows us to measure half of the *single* wave (from L1 to center/neutral) independently from the other half (from center/neutral to L2). Note the order in which I mentioned those: *L1 to N* and *N to L2* ... That minor detail is significant. Most oscilloscopes are ground referenced and you are therefore forced to measure from *N to L1* and from *N to L2* so you are measuring one half of the wave *backwards* from the way you are measuring the other half, so they *"APPEAR"* 180 degrees out of phase but they are *NOT* and cannot possibly be. A wave cannot be 180 degrees out of phase with *itself* . It is critical to keep in mind there is *only one wave* and the two traces on you scope are two halves of it. A Rotary Phase Converter does not take two waves which are 180 degrees out of phase and turn it into 3 waves 120 degrees out of phase. It takes a *single* wave existing between two points, adds a 3rd point, and the result is the creation of two new waves between the original two points and the new 3rd point, and the 3 resultant waves are 120 degrees apart. You can run a RPC from from a single phase 240V source which isn't center tapped and has no neutral. If there's no center tap, no neutral, no "180 degrees out of phase" legs and the RPC still works, then all this discussion about neutral and the 180 degrees out of phase waves was extraneous.
Doesn't "split phase" mean it is actually 1 - 240V phase, but the neutral is connected to the midpoint of the coil (and also grounded), giving 2 - 120V circuits that appear to be 180 degrees out of phase (you can still bridge the two hots or ends of the coil to get 240V)? There are lots of transformers, especially power supplies, that have more than one take off point on the secondary coil to produce different voltages.
If by "bridge the two hots" you mean "connect a load across both hots" and not "connect both hots together" then yes, I agree with everything you said there.
On a different note one could actually argue is single phase systems actually single phase if they have a center tap. Because really they could be used as single phase or a 2 phase system. I think the main point you got across is more the understanding what important about phase /polarity and how to take into account measuring for it properly in different types of systems. Very good video curious where you bought your variacator/ vfo equipment. Can it do nonlinear waveforms or just straight sinusoidal wave forms. Basically can it also be used as a full signal generator of any arbitrary wave form you want? And what frequency ranges can you generate with it at what current/voltage levels ?
Interesting argument about 2 phase, I don't think I could shoot it down without looking up some definitions but I can offer the fact that 2-phase systems do exist and they're basically 2 separate single phase systems that are 90 degrees out of phase with each other. As far as my equipment, for the 3 phase i was using an American Rotary ADX30 rotary phase converter which turns 240 single phase into 240 3 phase, and that fed into a 3 phase transformer to get 480V 3 phase. That is good for about 20A @ 480V. The variac was just a single phase 1.5kW variac off Amazon capable of 0-130V with 110V input. Nothing I showed is capable of changing frequency or waveform, just transformers.
If the centre tap is grounded, it's obvious the opposite ends of the transformer would look like it's "out of phase", they are just mirroring each other in opposite directions... A true 180° out of phase would be a generator with two or four phases, I don't even know if exists today, but in the early history I know they tested a different number of phases in generators.
There are some polyphase (>3 phase) motors used in the oil & gas industry I have seen, 6 phase and 9 phase, but these were powered by a special inverter and there was no generator outputting 6 or 9 phases. In the American northeast there are some areas that were electrified before much standardization had taken root, and they have two phase power. Basically two single phase supplies 90 degrees out of phase. This allows for a rotating magnetic field so motors didn't need start/run caps. This was/is inferior to the 3 phase we ended up standardizing on, since it also provides a rotating magnetic field but with only 3 wires.
@@charlesstaton8104 Very nice info, never heard of such things before. Thanks for this video btw. I have a deep respect for people who give their time for free to help teach others. Greetings from Brazil.
@@jptrainor my video demonstrated that the two halves of the single phase are in-phase and same polarity, but depending on how measure them, they may *appear* out of phase or inverted polarity.
With an isolation transformer powering the scope you could connect your probe's ground clip to L1 and directly measure the 240V waveform by probing L2 (or vise versa). But you could NOT clip probe 1 ground and L1 and probe 2 ground on neutral. *NOTE.* using an isolation transformer as described is *DANGEROUS* as it will elevate the chassis of the scope and every metal part of the scope to the voltage of whatever your ground is clipped to. *If you touch the scope you will get a 120V shock* and if the scope is touching anything metal it can short out and blow up. *NOT RECOMMEND*
I have been using an old 2 ch Tek scope for decades. No problem. Hook up the scope’s reference to the white center tap and the two probes to red and black. You see the two phases - 180 degrees apart.
Thanks for taking the time to produce this video, Chuck. A couple weeks ago, I decided I was going to understand split phase power. And now I do. Now I can explain it to someone else. Either 120 leg is basically a shortcut circuit within the transformer and the 240 is the full circuit. Thanks again.
Hey, 4th term electrical apprentice here in Canada. I think this cleared up a misconception I previously had when told our split phase system is 180 degrees out of phase; when I thought about it more it didn’t really make sense to me. So could I summarize your video by saying it’s really an issue of polarity when measuring from neutral/ground to either phase? Also, could you recommend a video that describes how transformers supplying residences are actually connected? I’m not sure I fully understand what I previously believed I had a good grasp of. I don’t know if I fully grasp how current is travelling.
_"could I summarize your video by saying it’s really an issue of polarity when measuring from neutral/ground to either phase?"_ Yes. The vast majority of people on both sides of the debate are using the term "180 degrees out of phase" to mean "inverse polarity." I highly doubt anyone is arguing that L1 leads or lags L2 by 8.3333mS (1/60Hz/2). I've had this debate with at least 100 people and not one of them has made that argument. It's technically not wrong to say "180 degrees out of phase" as a 180 degree phase shift is indistinguishable from a polarity inversion for a sine wave (not the case for asymmetric waves like sawtooth) but it can be confusing. For that reason I've started saying "inverse polarity" instead of "180 degrees out of phase." Here's an example I have been using recently: you have a 48V golf cart with six 8V batteries in series. You can look at it and see that they are all connected with same polarity ("in phase" - although that's a bit of a misuse of the term) and if you measure from one end of the series string to the other, you will see 48V, which could *only* happen if they were all connected same polarity. But if you measure from the midpoint between batteries 3 and 4, you'll see -24V, -16V, -8V, +8V, +16V, and +24V. Same thing for a center-tapped (split phase) transformer. The *apparent* polarity inversion is due *ONLY* to using the center tap as the reference point. One of your *MEASUREMENTS* has inverted polarity, but the *SOURCE does not.* Every one of the dozens or hundreds of turns of the secondary winding is induced with voltage of the same polarity, and current flows the same direction through every one of them. _"Also, could you recommend a video that describes how transformers supplying residences are actually connected?"_ Check out Dave Gordon's videos. This one seems like it might address your question, although I haven't watched it. ruclips.net/video/xMZkKI5rleg/видео.html _"I’m not sure I fully understand what I previously believed I had a good grasp of."_ Dave Gordon is an actual educator and his videos are better than mine. If you have any lingering misunderstanding about the topic of my video, check out his video on the same topic, it's much easier to follow than mine: ruclips.net/video/nOSYHUxHxG8/видео.html _"I don’t know if I fully grasp how current is travelling."_ Current flows the same direction through the loads on L1 and the loads on L2. I have demonstrated this in another video: ruclips.net/video/3PHjZOdqs1U/видео.html
This is all a waste of time. You do not have TWO independent isolated sources wit 4 wires that you can flip at your pleasure. The US split 120/240 system comes with 2 wires and the Neutral the phasing is already decided by the power company and is 180 degrees. Now, if you place an isolation transformer you can flip one of the phases but that is not whet the power company gives you.
I agree with every word of this (including the part about it being a waste of time) except for *"and it is 180 degrees."* If you have a single phase transformer with no center tap, current flows the same direction, and voltage is induced with the same polarity, in every turn of the secondary. Every one of 100s or 1000s of turns is in-phase with every other turn. This does not change if you locate the center turn, scratch off the enamel, solder on a wire and attach it to earth ground, and call it neutral.
@@charlesstaton8104 Of course. The center tap is the END of the first half of the winding and the Beginning of the second half of the winding. Therefore by forcing the center tap to be the common point one has no other option than measure the two winding extremes dereferenced to the center tap. Ergo the resulting opposite phase relation. These is all basic and very clear to anyone that learns science without the desire to be controversial at all costs.
@@geppettocollodi8945 I agree that it is very basic and very clear to anyone who understands the science, yet people still insist that two halves of a winding are 180 degrees out of phase with each other when they obviously are not. This leads to confusion among the less informed and further misconception. Do you know how many people think that current flows opposite directions in the loads on L1 and the loads on L2? It's a lot of people, and it stems from this false "180 degrees out of phase" notion. This is a philosophical debate really, like the old question "if a tree falls in the woods and nobody is there to hear it, is there any sound?" For some people, sound and voltage are human observations so a tree falling without an observer makes no sound and a voltage measurement IS TRUTH no matter the polarity. For others, sound and voltage are natural phenomena that exist independent from observation. If you can take two ground-referenced measurements, knowing fully well that they are being taken with opposite polarity from one another and insist that the two voltages *ARE* opposing, with no caveat that it only appears that way because one of your measurements are backwards, then you're in the first camp. The philosophical camp. I'm in the realist camp. Those voltages are *NOT* opposing, they only *LOOK* that way because one of them is being measured backwards. From where I sit, *YOUR* camp is the one being controversial at all costs.
I'm not sure exactly what point it is you are trying to make. What you are saying seems obvious. But I think a few misconceptions you may have are leading to misunderstanding. First, you referred repeatedly to apparent and actual values. Apparent and actual negative values, apparent 180 degrees out of phase, apparent polarity reversal. Apparent is actual. What you are missing is that there is no absolute ground point. Ground in a circuit is simply the point you choose as a reference from which to compare other points in the circuit. Voltage is the difference in electric potential between two points. It can be any two points you choose. The only thing that determines whether the value will be positive or negative is which of the points you choose to put your black lead on, that is your reference point for that measurement. This is true for polarity and also for phase. When we talk about two signals being out of phase, we mean the signals of interest. This is most often the output or input wave forms. In the case of residential electric supplied with 120/240V split phase service, the wave forms of interest are the two live or hot wires as referenced to neutral. The distribution transformer secondary winding is 240 volts between it's ends and is center tapped. The service drop is made up of a neutral line connected to the transformer's center tap and two lines connected to the ends of the winding which provide 120V with respect to the neutral line. As your demonstration shows, when you measure voltage from the center point of two batteries that are in series with the same polarity, one will read positive, the other negative. This is because your leads are "reversed" across one of the batteries so that the black lead is always at the center tap. It is important that we always measure the voltage from the same reference point within a given circuit, otherwise it is not very useful to us. Since we are defining our reference point to be the neutral conductor, which is connected to the transformer center tap, one of the live lines will have the opposite polarity to the other. This means the wave forms of the signals measured from neutral to each live line will be 180 degrees out of phase. The point is, it is the reading we get based on where we define our ground or neutral reference, that makes it out of phase, not the configuration of the transformer windings. I hope this helps to make this more clear and not less so. I would be happy if my EE education can help somebody else understand electricity, and I won't even leave you with a pile of student loan debt :-).
Wow, rarely does anyone disagree with this so respectfully. Thank you! I understand your point about apparent=actual for voltage, as it is a differential measurement like distance, and valid between point A and point B. Aville is 240 miles north of Bville, and home is right in the middle between them. There is a single car driving back and forth between Aville and Bville. If you're standing in Aville or Bville, it will look like the car is driving 240 miles away and coming back, but from the perspective of home, it will look like the car is driving 120 miles away in one direction and then 120 miles away in the other. And it won't just *look* that way, it *will* be doing that, since the measurement isn't how far the car drives, but how far it drives *from you,* the reference point. But I think it is important to have and maintain a concept of how far the car drives (not from you, but total) and what direction it's driving at any given time, because disregarding that data leads to fundamental confusion. I think most people see two cars in this exercise, which drive eternally in opposite directions, crossing precisely at home each time. This misunderstanding leads to other ones. Many many people think current flows opposite directions through the loads on L1 and the loads on L2 as a result of treating the measurements this way. I can't tell you how many times I've had to address that. When you're looking at L1 and L2 on a scope, you're looking at two halves of the same wave, current is flowing the same direction, and voltage is induced in the same direction. They have same polarity. One half of the wave can't be *actually* out of phase with the other half, because they're two halves of the same wave. You can make them look either way if you have an isolated scope; one way is more common and the other way is less confusing. The above is the better wording of my argument as informed by two years of discussion in this comment section and elsewhere since making the video. I hope this helps clarify where I'm coming from with regard to "apparent" vs "actual."
@charlesstaton8104 Not having the two years of updated info is a hazard when responding to older videos. It is a failing of mine that I often fail to notice the age of the video. They are all new to me. I haven't encountered anyone yet who was confused by the current direction, but then I am most often working with other engineers or electricians. As to your first comment about being respectful, I try to always use that as my default setting. I respect anyone willing to have a discussion. If we disagree, it just means we have more to learn from each other. I can't understand why some people think you have to hate anyone who disagrees with you. Anyway, best of luck with your channel, I hope you are successful in relieving people's confusion on this and other topics. There is much work to be done in that area.
@@jssamp4442 i don't know what it is about this topic in particular but it seems to bring out the worst in people, almost as if it were a political topic. I include myself in that; you may have noticed I had a certain "tone" or "attitude" in the video. That is because I recorded it in response to being beat about the neck and head over this in a forum. I had a bit of spite fueling me. That was regrettable, and I plan to record a new video, a followup of sorts, where I replace that attitude with the better methods I've found to explain this in the past two years, along with an objective explanation of the counter argument. Sort of "when people who know what they're talking about, say that L1 is 180 degrees out of phase with L2, here's why they are saying it. They're not technically wrong but if you repeat what they say without understanding these key concepts, *you will* be." I have heard the "current flows through L1 the opposite direction from L2" line from plenty of Engineers and Electricians. Recently I had a trio of Electronics Engineers with a combined >100 years of experience trying to force feed it to me on allaboutcircuits.com. I think if you did a little covert social experiment on your peers, find a way to organically get them talking about it, you might be surprised to find some of them believe this.
@@charlesstaton8104 LOL, you might be right about that last, but I don't want to lose my admiration for my profession. I think your approach to your new video is spot on. It can be so easy to put people on the defensive, and in that state it is nearly impossible for your message to get through. Another way to soften a critique that someone might otherwise get offended by is to use some version of FEEL, FELT, FOUND. "I know how you feel. I felt the same way. But then I found out..." It takes it from a lecture down to a word of mouth recommendation type of vibe. Of course it has to be authentic, something you really used to think but learned better or you might just come off as fake. Somehow I have picked up a strange mish-mash of communication skills in my nearly 60 trips around the sun. I never thought of myself as a good speaker or a teacher but my students seemed to think I did well enough. I was more surprised by that than anybody else. I look forward to seeing your new video when it comes out. I'll hit notify so I don't miss it.
Do some research on 2 phase in Philadelphia. It is actually still in use in some parts of the city. I have a milling machine and a lathe that both have 2 phase motors on them. I run them on a phase converter that was made in Philly. The motors have 8 wires instead of 9.
Yes I'm aware of it and have discussed it in other comments here, but intentionally didn't mention it in the video for fear of causing confusion. You're the first person I've ever "met" who actually has used the 2-phase stuff. I'm on a couple of machining forums and occasionally someone will pop up with a 2-phase machine tool asking for help. My suggestion has always been to upgrade to 3-phase, and since it's usually in a home shop, power it with a VFD. what's this phase converter? I've never heard of it. I know of the "Scott-T" transformer to turn 2-phase into 3phase and I know of the ubiquitous static and rotary converters which turn single phase into 3 phase but never heard of any kind of converter that turns anything into 2-phase. What's it called? Is it expensive? Does it require you to de-rate the motor and/or make the motor run hot? How does it work? Capacitors? Inductors? Rotary converter? Please explain. You've piqued my interest. Maybe your answers will change my boilerplate advice on the 2-phase motor dilemma.
Wow, I didn’t realize there was anywhere in the US that still has 2 phase. Thanks for that! There is a power distribution line out West that is still DC. I heard about it when in meetings with Electric Utility company about solar install plans.
@@charlesstaton8104 Sorry I didn't reply a year ago. The phase converter looks like a normal rotary phase converter. It has no start capacitors or relays in it, just run caps. I have run both machines on a vfd but never did any amperage measurements. It still remains a mystery to me.
it is a single transformer that is center tapped for 2 legs, therefore L1 to L2 is always the maximum voltage of 240 coming into the system, but when we need 2 legs of 120v each, there is only one way to do it, center tap! so both phases are out of phase in reference to the neutral(center tap) BUT if we do L1 to Neutral and Neutral to L2 then it is in-phase! but we don't draw the current that way in a split phase system, instead we have to do it with a common neutral so we go L1 to neutral and L2 to neutral! so they would be out of phase.
This is a great video for electrical geeks like us. For the overwhelming majority of non-engineering people out there, this is a distinction without a difference- the same argument as a single phase versus split phase system. I am a fan of using the correct terminology, but I find that mob mentality rules. I am in the solar industry, and it makes me cringe when I hear someone say "panel" instead of module. Two totally different things- one heats water, the other creates electricity. But the mob has decided there is no difference.
I really appreciate you doing this video. Apprentice Commercial Electrician about to Journey Out. This really put things into perspective compared to what the mainstream consensus is.
LOL can you expound on that? You're not the first to complain about the audio but most people don't have any issue. I think it might be a stereo/mono issue that only manifests on certain devices but I haven't been able to observe it on any devices I've played it on. Mind sharing what device you're using and what kind of speakers? Headphones? Mono/stereo if you know? Etc. I would like to get to the bottom of it and fix it if possible or at least not repeat the mistake on future videos.
@@charlesstaton8104 It just isn't synced. Sometimes I notice that while streaming a movie. Usually stopping and starting over fixes it, I didn't try it on your video however.
They are 180 out of phase because they share a common wire. you could have measured it wrong in the 3 phase too - why did you put all the grounds together. If you put two separate devices in each 120 line they can receive any phase. But if you plug two devices that share common ground in each of the two 120V lines they there is only one way to connect them -the common ground goes to neutral and they receive two 180 deg out of phase signals. Now I know this doesn't happen too often... Here is another explanation. In a schematic you point all the positive voltages and the negative goes to ground. If you have also negatative power supply you could argue that it's not negative and it's positive when you measure the other way, but when you have a common wire you only talk about polarity on the other wires with respect to the common one. so the two lines are out of phase with respect to the common wire.
It's like negative voltage in DC power supplies, depends on how it's measured, -12-0-+12, could measure as 24v, or 12v with opposite polarity, and 12v,
Thanks for the demonstration. Center taped transformers are simple. They do divide voltage an AC voltage. It is rare for people have a reason to poke around in a panel with an oscilloscope. My battery powered scope has common grounds so i would never hook it up the way you can with the fully isolated channels on your scope. Using a low voltage transformer to illustrate was wise on your part.
It is just a matter of how you look at it. The two 120v lines of a split-phase system are equivalent to two 120v lines which are 180° out of phase, however they were generated. It is just a semantic argument, not a substantive one.
@@GH-oi2jf if you have a 240" long board you can measure it from end to end and get 240". But if your tape measure is nailed to the middle of the board then you have to take two measurements; from middle to end#1, and middle to end#2, and add them together. But what we do for the classroom explanation for this L1/L2 thing is tell students there are two sticks, one having a positive length and the other having a negative length, and instead of adding them together we subtract because 120-(-120) = 240. Why do we reach around the world to scratch our back when the *_actual_* explanation is much more intuitive, and much more accurate? It is not merely a semantic difference when it leaves people thinking there are literally two sticks (because that's just what we told them) and confused about whether single phase is actually single phase or if it's two-phase, and if it leaves them unable to explain why they're subtracting the measurements instead of adding them like they know they should be. If you know enough to call it semantics then you get what is really going on, but many people don't. This video is for them.
@@charlesstaton8104 Sorry sir, but I find you video confusing. Now to be honest, I do no live in the US, so your strange two phase 180 degrees system is only for my curiosity. In Norway we used a 3-phase 230 V IT-network distribution system from about 1920 up til about 1995. From 1995 most new areas are provided with a 3-phase 230/400V TN-system. This system are now the most common distribution system in the world.
@@kjellg6532 the US system is silly, so don't feel bad if you don't understand it. I am silly too, so don't feel bad if you don't understand me either. The US system for residential is just single phase. Imagine a small single phase transformer for making 24 volts, some devices use low voltage AC like that. Now add a center tap to the transformer. You can measure from center to one wire, 12V. And center to the other, 12V. One wire to the other, still 24V. Still single phase. Adding a center tap does not add a phase. That's what the video is about.
@@charlesstaton8104 Now, let’s have a look: en.wikipedia.org/wiki/Split-phase_electric_power# This article states that we have two phases 180 degrees apart. In short, I agree in that. If you do not agree, please correct the Wikipedia article, everybody is free to add or correct a Wikipedia statement. As for the US system. In most of the world, appliances are made for 230V AC. The 230/400V TN system are in use in the grater part of the world. What does one benefit from the US split phase? A lower voltage. Not so harmfull if you touch it, but at the cost of much more costly copper in your house wiring. E.g. You charge a Tesla EV with 11 kW - in the US split phase system you need a 46A breaker and 10 mm2 wires - in Norway with 230/400V TN, you need 3*16A and 2,5 mm2 wires I do not see any benefits from using a split phase system. Do you?
@@charlesstaton8104 Another way of formulating this question: Split phase, US mains distribution. Let’s split one coil in half with a center tap (white). We connect a 2 channel oscilloscope with its common reference to the white center tap and the red probe to the live red wire. We see a sine wave on the scope. From a start point of 0V at zero phase angle the voltage increases to 120V when the angle reaches pi/2 or 90° if you like. (We leave out the amplitude and rms for now) If we connect the black probe to the scope’s second channel, we see a second sine curve on the screen. This curve will start at 0V and go negative. At pi/2 the voltage will reach negative 120V. The red voltage can be described with: V1=120*sin(ωt). The black voltage goes negative and can be described with V2=120*sin(ωt + pi). We see that the two voltages are both sine and separated with a phase angle of pi radians or 180°.
If you measure across the two legs, it is single phase 240. Measuring to ground they are 180 degrees out of phase. Unless working with a straight 240-volt device the legs are opposites 180 degrees out. Measurements should be made to ground in a home. Don't confuse the less experienced. Technically you are right but can be confusing to the less experienced.
Confusion of the less experienced is the whole reason I have such an issue with this; the whole reason I made the video. I struggled with this for a long time back when I was trying to wrap my head around AC fundamentals. People were insisting that the two legs *are* "180 degrees out of phase" or "opposite polarity" or "inverse" and I just could not make that make sense. The math said that if that were true, they should cancel out and yield zero volts. It took me a long time to realize that the reason I couldn't make sense of it is because what I was taught, and what keeps being repeated by people who know better, is wrong. It's fine in my book to think of them as being inverse or out of phase if that's how you were taught and/or that's how you've gotten used to thinking of it, so long as you know somewhere in the back of your mind that it only appears that way because of how we measure it. There are a lot of people who deny that "technically I am right" because they think the two legs *literally are* inverted from one another, and they defend that position with vigor. This video was meant primarily for those people. Secondarily it is for the less experienced. I just want to dispel the myth that the two legs are *actually* out of phase and encourage folks to recognize the importance of specifying your reference point (even if it's ground, even though it normally is ground) and when talking to the less experienced, maybe take the extra step of pointing out the effect of using the center tap as a reference (it makes one side *appear* inverted).
Thank you for making this video. Hopefully, your explanation will help others understand that the two legs are not out of phase. I’ve thought about making a video on this, but it would be more of a circuit diagram based explanation.
Not to dispute your findings but perhaps I can add here... the entire notion of "split-phase" is very easy to misunderstand. Yes, there is only a single phase entering your home but the 120V loads in the home are basically "split" in half. As far as the loads in the home are concerned, L1 and L2 are indeed 180° out-of-phase with each other WHEN REFERENCED TO NEUTRAL. Yes, each of the halves of the "split-phase" system are "in-phase" with each other (adding) when measured from L1 to L2 but when voltage is measured from the "Neutral" reference to L1 and then from Neutral to L2 the resultant measurement shows that L1 and L2 are indeed 180° out-of-phase WITH REFERENCE TO NEUTRAL. This is done so that 120V loads can share a common "Neutral" and the shared currents in that Neutral end up opposing each other because at any given instant, the currents between L1 and L2, each being 180° out of phase with one other are actually flowing in opposite directions in the Neutral leg. The result is that the currents algebraically sum together in the Neutral line resulting in a net Zero current (if the loads between L1 and L2 are perfectly balanced). In practice there is a non-zero current flowing in the Neutral but it is always less than the currents flowing in either L1 or L2. This is why electricians try to "balance" the load center, dividing household loads somewhat equally between L1 and L2. It is all about perspective or "reference" when measuring voltages in any system. You are measuring a voltage against a "reference" and in this case, the 120V, L1 and L2 loads in the home are referenced to Neutral.
I don't have any issue with what you just said, I agree completely. The key is that bit about "with reference to neutral." Voltage, being a relative measurement, always must have a reference, and for residential power that reference is almost always ground/neutral (not interested in getting into the weeds about the difference between the two at this tine). So it is intuitive to think of L1 and L2 being out of phase because that's how it looks on a ground-referenced scope. But to say "out of phase," without the stipulation of "with reference to neutral" to qualify it as a relative measurement, is to assert a non-relative reality. What people are saying when they say "out of phase" and stop there without specifying it as a relative voltage measurement, is that the two halves of the transformer are physically out of phase. That misstatement is what I take exception to, especially since it seems to me that most of the people saying it don't realize that it's a misstatement and will even try to battle you over the matter.
@@charlesstaton8104 I agree with that entirely. It is the "two halves of the transformer being out-of-phase with each other" idea that I think folks have a hard time with. Thank you for your work and video's, good information.
The fact that the neutral currents nullify one another from equally loaded L1 - L2 120v branches should lead the reader to question the concepts being discussed. Polarity inversion and 180° phase difference are the same thing.... Period. This respondent correctly addressed the issue at hand "how are we referencing the measurement?".
@@charlesstaton8104 How exactly do electrons flow in a split phase system? No matter which way it is, there has to be at least 2 conductors where electrons are flowing to the load simultaneously at any given time right, so if that is true then how would there be voltage across those 2 lines at that moment? Im genuinely curious and am having a difficult time understanding
@@FearfulFellow Electron flow is something I never found any practical reason to study. I don't know enough about it to give you the kind of answer you're probably looking for. There is however a practical reason for understanding the difference between two waves that are actually out of phase and waves that only appear out of phase because of where you measure them, and that's all this video was meant to address. Electron flow is more abstract and academic and I have no plans on covering it.
14:40 is what you need to show people who argue split phase is 180* out of phase.
But split phase is in fact two sine voltages 180 degrees apart. Lol
@@kjellg6532 in reality its one sine referenced at different points, in this case to a center tap, to itself. when playing with a scope you realize the second wave is simply the opposite swing of the same wave referenced. In short its the same wave looked at in different angles.... your up is chinas down but in reality its just down, to each persons reference
I looking to run a 240-volt mini split off a solar generator with L1 120v and L2 120v off the same inverter think this is possible?
"Solar generator" = inverter?
Does it have L1, N, L2 output? Or just L, N?
@@charlesstaton8104 a 5000 watt inverter with expandable battery capacity (not split phase just one inverter) with 2 120v 30 amp outlets. I was looking to see if I can run leg 1 off of one outlet then leg 2 off the other outlet to the 240v mini split. The mini split has an inverter to DC to run the compressor motor and the fan motors. Sorry if this is confusing.
@@ryanevans7253 i don't have enough information to answer. It has 2 outlets but they might just wired in parallel inside. It might only output a single 120V. You might want to ask the manufacturer. Or tell me the model # and I will look it up later (out of time for now).
@@charlesstaton8104 thanks for your help I will try to get some more information.
Nope, I didn’t skip any of it.
I saw you state lots of stuff that, while technically correct, in the real world is not valid. Then, almost as an aside, tell people not to do it.
My point was, it’s not a valid measurement for the vast majority of technicians who may be watching, let alone the diy brigade.
I’m pretty sure you’ll find you absolutely can treat L1 as a source and run all your loads between that and neutral. Please don’t though. Your power company won’t like it, any more than they would an unbalanced 3 phase supply.
The reason I made the video is because the "technically correct" part seems to be glossed over by many educational resources and therefore unknown by a lot of (maybe most?) people. Loads of people think L1 and L2 *actually are* out of phase, and defend that idea with an unreasonable level of zeal. Treating L1 and L2 as being out of phase or opposite polarity might not cause you to get wrong answers on a test over Kirchoff's laws, but it leads to further misconceptions, like that current flows opposite directions through the loads on L1 and the loads on L2. Do you realize how many people actually think that? If you're of the opinion that I'm being pedantic and making something out of nothing, try asking around to different people you know (electricians, technicians, electronics engineers with 40+ years of experience) about the direction of current flow through L1 and L2 loads; I think you will be appaled.
By your incorrect theory, L to L would only ever be 120v. If you set your scope to trigger on CH1 and put one probe on L1 and one probe on L2, you'd see that when L1 is 120v peak above 0, L2 would be 120v peak below 0. L to L is 240v peak. Your arbitrary changing of reference to suit your theory is incorrect.
Let's say there are six 6V batteries in series, but you can't see the polarity. There is no ground, no predefined reference point. You measure from end to end, and you get 36V. From this measurement alone you have proof that all six batteries are connected with the same polarity because their voltage adds. If one of them were connected with opposing polarity, it would subtract 6V from the total, leaving 24V. If two were opposing, 12V. If 3 (HALF) were opposing, you would get 0V.
You can do the same experiment with AC sources instead of DC sources. Instead of six 6V batteries, use six 6V isolation transformers. Again, if the six transformer secondaries are all connected with same polarity, the total voltage will be 36VAC. If one is reversed (AKA out of phase) then the total voltage will be 24VAC and if two are reversed (AKA out of phase) then the total will be 12VAC. And if 3 (HALF) of the source is reversed (AKA out of phase) then the overall voltage will be 0V.
We know just by the fact that that sources add, that they are IN PHASE with each other. Choosing one specific reference point and calling it the holy reference point and refusing to ever take any or acknowledge any other measurements with reference to any point other that the holy reference point does not change that. Just because the waves *_appear_* inverse on your scope screen does not mean that they *_are_* inverse. They only *_appear_* that way *_because_* of the insistence on using the center tap of the transformer as reference. The same thing would happen in the six-battery series string if you welded your black meter probe to the jumper between battery #3 and battery #4. Batteries to the left would *_appear_* to be "negative" while batteries to the right *_appear_* to be positive.
This can be harder to conceptualize when there are only two halves to measure instead of six separate sources which is why I bring up six sources. But hopefully it is obvious that they are equivalent, whether six or two, and whether AC or DC. If half of the source is inverted then the total is 0v, while if it is non-inverted then (regardless of appearance which is purely a function of chosen reference) they add. If they add then it is impossible that they are anything other than in-phase AKA same polarity.
I am well aware of the confusion our residential system has caused some and while I feel I have a pretty solid handle on it I thought maybe someone had rediscovered the wheel in explaining it. A few minutes in the video it started reminding of the super geeks in college getting into rage'rs over simple concepts like semantics. Thinking I was missing the brilliance, half way through I moved on and I casually listened while reading comments. This effort provided no additional sense of discovery and it became clear this video was just a muddy mess of an effort of trying to hard. Fortunately I read @Brokendiode (Retired Engineer) about half way down and his comments made me realize the audio had ended, reading the rest of the comments wasn't going to provide the eureka moment and I wasn't crazy.
Look, there is a reason the white neutral in a 3 wire multiwire branch circuit is the same size as the Black L1 and Red L2 and NOT twice the size. And it's the same reason why older (mechanical) 240v stoves, dryers, pumps etc didn't even have neutrals. The return bath in each of the circuits is the other hot leg. Black returns on the red, red returns on the black. They are each others neutral because they are OUT of phase. Now they couldn't function that way if they were in phase. If you doubt that and are insistent they ARE in phase, it's pretty simple to test your theory. Open your panel, find a DPST breaker. Remove the red conductor and land it on the next breaker down (it will have a black). Close both circuits. How did that work out for you? (I'm not responsible if your theory has unexpected results.)
Guys, this is not rocket science. N to B and N to R are 180 out of phase. The only way B and R can be measured IN phase is if you move your reference across the windings. Measuring N to B and R to N would be in phase. Of course this would just be an academic exercise as nothing is wired this way and therefore has no practical application.
Let’s do a simple explanation here. I’m going to assume that you know complex numbers. Let’s assume that you claim that L1 and L2 are out of phase.
So let L1 =
120( cos(0°) + j_sin(0°) ) = 120.
Let L2 =
120( cos(180°) + j_sin(180°) ) = -120.
The j_ denotes a complex part and since the sine of 0° or 180° will be 0 then we don’t have to consider it.
Adding them up and NOT subtracting since the waveforms are added you get 120+(-120) = 0.
This means that L1+ L2 if they really are out of phase then the resultant waveform would cancel itself out and hence you are left with a voltage across L1 and L2 that is 0 and NOT 240.
Now if they would have been In Phase with 0° between the waveforms then the resultant would have been 240 volts. So you’re premise of them being “out of phase” has been proved wrong.
ruclips.net/video/nOSYHUxHxG8/видео.html for an alternate explanation that shows how many aspects are the confusions about 'convention', and which ones are in use.
That's an excellent video. If it had been posted before I made this video, I never would have recorded it.
With respect to two single phase loads (one on L1 and one and L2), the current flowing through them is 180 degrees out of phase to one another. If I have two equal loads (for instance two 60W light bulbs), there will be no current flowing in the neutral. They cancel each other out because they are 180 degrees out of phase. The two loads at that point look like one 240V load with 120V dropped across each and the current alternates back and forth through them without ever going through the neutral.
Here's a little thought experiment (or you can do it in real life if you want):
I agree that no current will flow in the neutral, so let's get rid of that neutral connection; it's not doing anything. So we have L1->bulb1->bulb2->L2. Nothing changes right? Neutral was functionally absent and now it's *actually* absent. Put a mental amp clamp around the L1 wire coming out of the wall, and slide it down the wire until you get to bulb1, slide it over bulb 1 (really small bulbs) and toward bulb 2. Slide it over bulb 2 and along the L2 wire back to the wall.
In your head did you see the current waveform spontaneously invert its polarity at any point? If so, when (at what point)? And why? And what would have happened if there were 3 resistors in series, rather than two?
@@charlesstaton8104 I'm sorry if it seemed that I was disagreeing with you. I do not. Just pointing out how it looks from a common reference point perspective with the current. Good video. BTW have you seen this guy's video. He goes through all of the same demos that you do, but he has an awesome setup. ruclips.net/video/nOSYHUxHxG8/видео.html
@@srtamplification yep, that's an excellent video. Better than mine, I admit. Easier to follow. After watching it I think I understand where you are coming from but if you go back to his video where he demonstrates the amp clamps on L1 and L2 and contrast it with the thought experiment i described, you might notice he's measuring current backwards on one leg compared to how he did on the other. I wish he hadn't done that because it's confusing and not consistent with the rest of his video. Current flows the same direction through both bulbs. The reason no current flows in the neutral isn't because of any cancelation of opposing currents but because the loads are balanced, which he did a great job of explaining.
But you can't just "get rid of the neutral for a "thought experiment", if you go and do the math on this subject , THATS where you get 180° phase shift. Because for voltage to HAVE current, you have to have a "neutral" , and THATS precisely what makes this a 180° shift, and what gives you 240v /120v-to-neutral in "power". @@charlesstaton8104
Don't trash the dino scope. You probably only fried a rifa input filter cap. A few cap upgrades and you should be good to go
I gave it to a beginner on an electronics forum who didn't have a scope and was eager to try repairing it.
Excellent explanation. The fact that it's called "single phase" should be enough for people. By definition, something that is "single" has nothing to be out of phase with. Yet the misconception persists . . .
A single phase on the primary winding of a transformer CAN, in fact be split at the secondary into TWO phases. That's exactly What happens at the pole and dine every day. When you mention the word phases it is important to specify your reference point.
In a residential elect circuit each side of the secondary of the pole transformer is labeled L1 & L2 with the center tap of the transformer called the Neutral. So when measuring:
L1 & neutral 120v single phase
L2 & neutral 120v single phase
L1 & L2 240v single phase.
However L1 & L2 are def out of phase when referenced to the neutral
@@rty1955 wouldn't it be L1 & L2 240 volts split phase though and not single phase. Also I'm having a hard time understanding what he is getting at in the video. Why is he saying they are not 180° out of phase?
@@anthonyesposito7 yes it IS split phase. You are taking a SINGLE phase and creating 2 phases. A phase is an angular difference of the original signal. Therefore at the secondary there are TWO phases relative to the NEUTRAL. Like I said, it depends on your point of reference.
So when you say L1 & L2 IS single phase with respect with each other, however if your reference your measurement from the neutral, there are two distinct phases
Helps?
@@rty1955 Yeah thanks, I actually went to Dave Gordon's channel and he explained it a little better the this video at least it made more sent to me. I completely understand now that it really is a split single phase but also L1 and L2 with reference to N are NOT 180° out of phase in that respect. I went into this video with that assumption but as Dave points out in his video is that for them to be 180° out of phase the physical windings on the transformer would have to stop at the point were the neutral is tapped and then begin to wind the other direction relative to the first half of the windings if that makes sense. Dave Gordon has a really great channel too if anyone is interested in more stuff like this.
@@anthonyesposito7 well not at all. L1 IS 180° apart from L2 with respect to the neutral. So the OUTPUT of the transformer is effectively two windings that are 180° apart. The INPUT is single phase.
I say effectively because if you took 2 different transformers with the input sides wired in parallel and the output wired in series.
So the output would look like C for the common of the two transformers (A&B) and T1 for the other side if winding from transformer A, and T2 for the other side of transformer B Then used a scope to look at the output phases they MAY be in phase, if you measured from C to T1 and C to T2. But, flip the T1 & C and they will be two different phases with respect to C.
don't overcomplicate the things, you should connect them right. you are just making people confuse.
According to the large majority of the comments here I am not just making people confused. I am helping them understand. Many "thank you, I finally understand" comments. Maybe I am making just you confused. Not everyone receives information the same way; if there's something you would like for me to explain in a different way, let me know.
It never made sense to me that the 2 legs of a split phase service could be 180 degrees apart, because the inductive field of a single coil cannot be made to selectively invert a part of an AC waveform with a mere center tap connection. And of course, as you point out, the resultant voltage of the opposed phases would be zero. The entire phase converter industry would have disappeared overnight as a consequence of such a discovery, yet many people continue to believe that this is the case. Great video and explanation, lavish with lots of patience and nuance, I intend to watch it at least several more times.
EXACTLY!!!
Sorry, but the two 120V are 180 degees out of phase. For a moment, look to a 3-phase system. If you draw a phasor diagram, the vectors all start in the centre, the neutral point. They are 120 degrees apart as the coils in the generaor are placed 120 degrees apart.
Each coil producing 120Vrms in the US. The voltage between any two line conductors will be 120*sqt(3) = 120*1,73=208V. This voltage of 208V is the vector sum of the two 120V voltages.
Now, we take one of the three coils out and turn the two so their phasor points directly opposite. What is the voltage from phasor to phasor: 120+120-240 V. The two voltages are 180 degrees out of phase.
What if we place the two coils side by side? The two phasors will run totally in parallel, or we would say - in phase! . What is the voltage measured between the arrowhead of the two phasors? 0 volt, zero.
The two 120V are now in perfect in-phase and creates a voltage of zero volt.
The fog for me disappeared the moment I thought of a center-tapped secondary transformer coil. Of course, this is exactly how power is produced on the last leg to a residence.
How could the end-to-end leads of the secondary be out of phase? It's just one coil of wire! There is only one phase... The center tap just halves the voltage of the single phase result.
Exactly! That's what I've found is the most illuminating way to get the point across. If you read through the comments here, the arguments usually stop when I say that. The detractors usually won't admit it but I think that bringing this up is helping people realize what is actually going on.
@@charlesstaton8104 Another way to look at it is with a Mattel Hot Wheels track in a loop with one or two power boosters. Power boosters are like those spinning wheel baseball pitching machines.
Anywho, one power booster is half the secondary coil. The full secondary coil is *both* power boosters. Things are gonna be moving along just a bit faster!
Obviously, it's not a perfect analogy. But, no model is perfect.
Thanks for bothering to take the time to put up the video. It's always neat to see how others see things.
If, and nearly only if you live in the US. In the grater part of Europe most houses now get 230/400V 3-phase TN network.
People who don't understand the point of reference when making this argument simply don't understand it at all
Excellent presentation. Anyone with knowledge of these circuits will agree with you, but it may be bit confusing to those who are still trying to grasp it. I didn't say learning because we are all still learning.
Anyhow, whenever someone challenges me on this subject I simply ask them this: How can you get two separate sine waives off one phase of power? Answer, you don't.
For an explanation, look no further than the utility transformer that is wired for 120/240 volt service. You'll note on the primary side of the transformer that the H1 bushing is connected to only one high voltage phase, which will be 7200 volts phase to ground. The H2 bushing will be connected to ground/neutral. No other connections on the primary side exist.
Quick note, the primary/grid side on a single phase is 7200 volts because it is a line to ground reference. On the same system, the line to line reference will be 12,480 volts. This is true on a 3 phase system because you must first find the square root of 3 (1.732) to find the answer. Simply multiplying 7200 by 1.732 you'll get 12480.
What comes out of the "split phase" secondary is 120 volt to neutral from each of two legs (X1 and X3 bushings) which then go into the establishment. X2 bushing is connected to ground/neutral which then also goes into the establishment.
What you'll get is a phase to phase voltage reading of 240 volts and of course 120 volt from either of the phases to neutral. But they are more accurately called legs because in truth there is only one phase coming from the utility, hence single phase. Since it is only a single phase, then the obvious outcome is there is only one sine waive. Done!
The discussions in the comments on this video have led me to the realization that I could have explained it better by leaning on the points you highlighted. I was trying to approach the topic on the same playing field that the counter-argument resides on, but it's not the right playing field and the game is rigged.
The video would have been better if I stressed the fact that there is *only one sine wave* and it can't possibly be out of phase with itself. When we measure it, typically our equipment forces us to take two separate measurements of two halves of the single wave and add them together, but that doesn't mean there are two waves. One wave; we measure one half and we measure the other half. One half *appears* out of phase with the other half because typically our equipment also forces us to measure the second half "backwards" with respect to how we measure the first half. I think that explanation would be easier to digest for the newly initiated (and for the old bumps on logs who have known the "truth" of the matter since before I was born).
Vab = Va - Vb
This is splitting hairs, but you don't add the sinusoidal waveforms to get the voltage between two lines. You are finding the difference (subtraction) of one sinusoidal line to neutral voltage from another sinusoidal line to neutral voltage with the opposite phase. For sinewaves there is no distinction between a sign flip and a 180° phase shift.
240 = 120 - (-120)
You have a neutral wire and two hot wires. You don't have a neutral wire, a hot wire, and an "extra hot" wire in a 240V split phase setup.
@@jessstuart7495 can you articulate why in this one isolated case the voltages should be subtracted when in every other case of wave interference* the amplitudes are added?
*consider sound waves, ocean waves, light waves, kinetic vibrations, AC electrical waves in every instance but the L1/L2 phase debate, etc.; every kind of wave physics knows of. Converging waves add. If they are in phase the resulting wave has greater amplitude than either of its constituents. If they are out of phase, the resulting wave is diminished. It's how noise canceling earphones work.
@@charlesstaton8104,
It's because potentials are defined relative to a arbitrary reference level. Potentials are just a mathematical convenience that makes solving circuits easier. Voltage is deliberately defined so the gradient (spacial derivative) of the voltage (potential) is equal to the electric field. It is the electrical field that applies forces to charges. When you "integrate" the electric field to define the electrical potential, an arbitrary constant of integration is always there, even if you chose this constant to be zero.
Electrical fields and node voltages add (superimpose), but when you are talking about the voltage across a device, this is equal to the difference in node voltages.
Here's a DC example. If one side of a 1kohm resistor is connected to the positive terminal of a 9V battery, and the other side is connected to an LED with a 3V turn on voltage, and the lower side of the LED is connected to the battery's negative terminal, there will be a 6V across the resistor (Kirchhoff's Voltage Law).
A multimeter will measure voltages in RMS, which is always a positive quantity. It appears like the hot to hot RMS voltage is the sum of the hot to neutral voltages, but this isn't really the correct way to think about potentials. Again, I am splitting hairs here.
@@jessstuart7495 the DC example I like to use, is two 12V batteries in series. With a string of any number of batteries where the voltages add, like on a golf cart for example, almost anyone would find it intuitive to lift both DMM probes off the batteries, measuring from + to - of each battery. If you had two in series you could look that them and tell right away without any measurements that they have like polarity. But if you couldn't see the markings, a quick check from the negative terminal of the first to the positive terminal of the second, would tell you that they have like polarity if 24V is measured. But if instead you *_arbitrarily_* (as you mentioned) decide to pick the node between the two batteries as your reference, permanently weld your black DMM probe to that junction so that no measurements can be taken with reference to any node but that one, you would measure -12V to the first battery and +12V to the second. Since this is a very basic situation and you *_know_* that the two batteries are actually, physically, connected in series with like polarity, then you *_know_* that one of your *_measurements_* is being taken with opposite polarity. Since you *_know_* this, rather than correcting the sign of your backwards measurement and adding the voltages as one should, some may find it more intuitive to change the sign of operation rather than the sign of the value and say +12V-(-12V)=24V. That's just fine with me, if your numbers are just for your own reference or if everyone you're sharing this data with is on the same page. What I have a problem with is when this ends up getting taught and regurgitated by the masses who *_aren't_* on the same page and *_they actually think_* that one of those batteries has opposite polarity from the other one, and for reasons they can't articulate, we subtract in this case instead of adding. Since you can articulate the reason, I would like to make you aware that not everyone is on the same page. The way that you're wording things, the established way of wording things, is misleading. There is a fundamental misunderstanding rife in the community as a result. If you think I am splitting hairs, just ask around. I think you will be surprised at how many people actually misunderstand this.
@@charlesstaton8104,
Maybe "stacked voltages" is a better way to say it.
This video provides one of the best explanation of the concepts.
Two voltages of equal magnitude that have the same polarity(0° in phase) and placed in series sums.
Ex: 120v + 120 = 240!
However, if one the voltage is 180° out of phase(reversed polarity) their voltages still sums!
Ex: 120 + (-120) = 0
But it's impossible for a spilt-240 v service to be a 0v line-to-line and still give 120v on line 1- neutral; & line2-neutral!
0° to 180° is a straight line which has no angle!
If two sources are 120v each and are not in phase the sum of their voltage is less the 240!
Kirchhoff's Laws might help out here:
1) The sum of all currents entering and leaving a junction add up to Zero
2) The sum of potential drops around a closed circuit add up to Zero
Your presentation has initiated some great unrelated thoughts:
If we imagine a voltage supply transformer of 240v feeding two resistors of 4ohm and 2ohm connected in series then the current flowing in the circuit is 240÷6=40amp
Now if we centre tap the transformer and create a neutral path between the resistors and feed each resistor with 120V we will have two separate closed loop circuits.
The current flows will be as follows:
120÷4=30amps
120÷2=60amps
At the node point of the two resistors and the neutral we will have 60amps flowing into it from the 2ohm resistor circuit and 30 amps flowing away from it to the 4ohm resistor circuit. The other 30amps will flow down the neutral to the centre tap of the transformer.
At the centre tap of the transformer we will have two currents flowing in, each of 30amps, one from the closed loop of the 4ohm resistor and the other from the neutral. These currents will add to give 60amps which will then flow in the closed loop of the 2ohm resistor circuit.
I am not sure how relevant this is to the current discussion and hopefully my analysis is correct.
So, the limitations of the older oscilloscope (being forced to use ground as a reference point) is what started all this confusion.😂
Best explanation I’ve seen for this. I’m keeping the link for the next time are argue with someone about this. 😂
When you hook the positive of One battery to the negative of the other battery why did it not short out is that just cuz you didn't have the two batteries in the same circuit
And we’re back to ground, again.
The circuit includes the ground and the axis is conventionally placed on ground, so everyone sees the same thing, when looking at waveforms.
If you’re going to do something unconventional, your results are going to look different from everyone else’s. Ultimately, current is electron flow and will always try to flow from more negatively charged places towards less negatively charged places.
Over the years, the way we reason that out has changed and will doubtless do so again, but for now, the convention is to plot graphs relative to zero and zero is whichever leg is grounded.
That’s just the way it is.
Thank you for connecting the oscilloscope with both ground references together, at ground, on a dual trace scope. This proves beyond the shadow of a doubt that there are TWO 120VAC phases, and they are 180 deg out pf phase. We measure 240VAC because of the absolute voltage compared to ground, between the 2 hot legs. The title of your video is deceiving at best, and dangerous at worst. It's time to adjust your understanding, rather than trying to change physics.
Nope. Single phase is *SINGLE* phase. Not sure why you would say otherwise.
Take an isolation transformer with no center tap; current is flowing the same direction through, and voltage is induced with the same polarity across, each and every turn of that winding. Agree?
Now identify the very center turn of transformer, scratch the enamel off it, and solder a wire on. Did you magically invert the polarity of half of the winding? No you did not. Connect that center wire to an earth rod and call it "neutral." NOW did you magically invert half the winding? No you did not.
You just created a split phase transformer exactly the same as pole transformer and the two halves of it are *NOT* out phase with each other or inverted with respect to each other.
Not sure why the truth is so "dangerous" in your opinion.
@@charlesstaton8104 "...magically invert the polarity..."? No, it's not magic. That's simply the way it IS, when we measure in reference to the center tap. If we split the winding at that point, THEN we have two coils in the same phase. It's telling, that all the demonstrations you did prove that point, and yet you insist on understanding it incorrectly. It's much simpler than all the man-splaining contortions. Get your money back from whomever taught you incorrectly.
@@stirlingschmidt6325 so adding a center tap *DOES* invert the polarity one half of the transformer, but just not magically? Got it. Great explanation, really. Thanks.
Just one question though, if "magically" doesn't describe the phenomenon, what word does? Spontaneously?
I noticed you started using the term "with reference to neutral" which I am a big fan of forcing people to use, since it is the first step toward realizing that they are measuring two halves of a series string of voltage sources (each turn of the secondary around the core can be considered a separate series source) from the center outward, so one half is measured with opposite polarity from the other, thereby making one half *appear* inverted from the other.
@@stirlingschmidt6325 It's the exact same coil of wire, it's the same phase, maybe you should get your money back for whoever educated you.
Hey man, nice video and great discussion. Not trying to change your mind, only offer a different perspective and way to conceptualize this. As you probably know in AC circuits there is no positive voltage or negative voltage. Only electrons flowing to and from the source due to transition of north to south magnetic poles in the generating equipment.
Much like two cars traveling the same speed in exactly opposite directions the relative speed to each other is double not zero. If you were to observe one of these cars and you were standing still their speed would 1/2 their relative speed.
For a US split phase residential service the common reference point is the center tap of the step down transformer. much like the mid point of a North to South magnetic field where the magnetic field is parallel to the coil (eg 0 flux eg 0 volts eg neutral) center tapping the secondary creates a new reference neutral point.
Voltages to the left and right from this new neutral increase proportionally in opposing poles (North and South)
I think where you’re confusing people is intermingling direct current with AC circuits. There is no positive or negative in AC. Only voltage differential caused by phase differentials which don’t cancel out.
When you’re measuring a peak wave to another peak wave below your reference point the peak wave below the reference point is not negative. Think of the Peaks as a North Pole peak and a South Pole peak. And we all know the max potential force is measured North to South.
So yes, split phase 120V services are exactly 180 degrees out of phase. If they were anything else they would not be exactly double their additive values. For example if they were 120 degrees out of phase their additive value would be 208V. Eg a 3 wire network service.
Hope this helps, look forward to any discussions.
"in AC circuits there is no positive voltage or negative voltage." - yea there is. Voltage always has a polarity. In 60Hz mains AC, the polarity changes 60 times per second.
"Only electrons flowing to and from the source due to transition of north to south magnetic poles in the generating equipment." - when electrons flow (current) through a resistance they create a voltage, and that voltage has polarity.
"Much like two cars traveling the same speed in exactly opposite directions the relative speed to each other is double not zero. If you were to observe one of these cars and you were standing still their speed would 1/2 their relative speed."
- for center-tapped *single phase* electrical supply, the more accurate car analogy is that you the observer are standing in the exact center of a 1/4 mile drag strip as a *single car* races from one end to the other, turns around, and races back, turns around, and so forth. The parameter of interest isn't that car's speed, but its *distance* from you. That car is going a full 1/4 mile each time it turns around, but Since you're in the center of the track, it *appears* to only go half that distance. So what is this car 180 degrees out of phase with?
"For a US split phase residential service the common reference point is the center tap of the step down transformer. much like the mid point of a North to South magnetic field where the magnetic field is parallel to the coil (eg 0 flux eg 0 volts eg neutral) center tapping the secondary creates a new reference neutral point. Voltages to the left and right from this new neutral increase proportionally in opposing poles (North and South)"
- continuing the single phase/single car analogy, since you're in the center you think of yourself as the starting line, as the "zero." Since you're "zero," we say that when the car is on your left its distance (from you) is negative and when it's on your right its distance (from you) is positive. But your position is arbitrary. You could have chosen to stand anywhere on the track. You could have chosen to stand at the end, where the driver of the car would probably consider the "zero" point. Then its distance would go up to 1/4 and down to zero and back up to 1/4 mile. Your choice to stand in the middle does not cause a second car to materialize on the track driving ever in the opposite direction of the first car. There is only one car. Only one phase. Only one wave. That car/wave/phase *cannot* be "180 degrees out of phase" with *itself.*
"I think where you’re confusing people is intermingling direct current with AC circuits." -am I confusing people? From all the other comments it seems I am not. I like to use DC analogies as far as I can take them because batteries are much more intuitive for most people, and in this video I went about to the limit of where you can apply DC analogies. Any more in-depth and I would have had to abandon them.
"yes, split phase 120V services are exactly 180 degrees out of phase." - I'm sorry, but they are *not*.
"If they were anything else they would not be exactly double their additive values. For example if they were 120 degrees out of phase their additive value would be 208V." - if they were 180 degrees out of phase their additive value would be *zero* as I repeatedly demonstrated, not double. You get a doubling when two waves are exactly *in* phase. But in the case of center-tapped single phase, there is only a single wave and instead of measuring it directly, typically you're measuring one half of it plus the other half of it. Since you're measuring these two halves with one set of probes backwards, the second half *appears* reversed.
"Hope this helps, look forward to any discussions." - I hope this is eye opening as well.
For another perspective on AC phases, see this: ruclips.net/video/quABfe4Ev3s/видео.htmlsi=9GJ3g7U2zBrEsXRc
So it is 180 degrees out of phase you just have to wire it properly.
Oh, ok. I never even considered wiring it properly. I'll have to try that next time.
Didn't get this in my teens and twenties, and still don't get it in my sixties, even after retiring from thirty five years in aviation. Thanks, anyway.
Really appreciate this. Was perplexed, out of phase did not make sense to me, but everyone said so. Thank you.
10:11 "Is the source out of phase, or is the measurement device out of phase?" 👈 Good to keep in mind - Keep the meter clips on the correct legs!
Damn, I remember browsing youtube many years ago and being confused about - how the hell just adding center tap can invert phase?! And almost every popular youtuber and even pro electricians couldn't explain it lol. Turns out it is just a measurement problem.
Wonderful. Thank you. raphael nyc
DC does not have a phase it could have a frequency if it's pulsating DC current. All I can say is homie needs to lay off the Red Bulls. I do understand his point but trying to explain this to someone that does not have a clue would be like lost
😄 thanks for the feedback. I'll make sure to leave redbulls off the menu going forward.
I did the same experiment but used a multi tap transformer used for HVAC. This is perfect to get people to understand how split phase truly works, and just how important your reference is.
Wow. I did not understand why they used 3 phases. Now I do.
Great video. Have you heard about "balanced AC power"? This is a special installation for recording studios and other facilities where stray ground current can be an issue. You have a transformer with a 120 volt center tapped secondary. The center tap is grounded and your equipment connects across the two 60 volt legs of the transformer, which as this video illustrates are in fact single phase 120 volts. This configuration reduces stray ground current. Article 640.9(A) of the NEC covers this type of system. Labeling and color codes are strictly spelled out as the so called "neutral" side of a receptacle is now 60 volts to ground at full breaker ampacity. Double pole tied circuit breakers are also mandatory and a dedicated breaker panel must be used. In essence, a balanced 120 volt power system is exactly the same configuration as standard split phase residential in the USA but it's 120/60/60 versus 240/120/120 to the grounded center tap.
No I have never heard of it so thank you for the info. I love to learn new things.
You could get yourself differential probes for your Tek (BTW, my Tek also had a cap fizz on me, must be a Tek thing. I use my Rigols now), or any other scope I imagine. I use the simple mod that you mentioned to keep from vaporizing my ground lead, and with the plastic-cased scopes these days it's not as risky as it once was.
I gave the Tek to someone on the internet. A newbie who wanted to try fixing it for experience, and was hopeful to get a free scope for the effort. Not sure if they ever got it working.
@@charlesstaton8104 That's the right thing to do in my opinion. I'll eventually find someone in need of a scope (and it still works even with the blown cap).
@Robert Swaine Old analog scopes aren't really worth the trouble, they are useful for analog-ly things like power supplies. I'm very fond of the Rigol products, not only are they very affordable, but delightfully hackable (hint: don't buy the upscale model without checking what you can do with the base model).
And then there's the FNIRSi ADS1014D scope/frequency generator & counter for $185. Runs off of USB power or the adapter. It's a cheap, fairly capable scope. Good for 400 Volts - until it isn't. :)
Split phase is defined as a center tapped transformer L1 to L2 is 240v RMS. The center tap is defined as neutral and is also tied to ground at one point. We all realize it is 340v peak to peak. For apartment work, split phase is not two legs of the three phase system.
Yes, and no. A 3-phase system has 3 coils 120 degrees apart. Each coil producing 120Vrms and the vector sum between two coils is 208Vrms.
Now let us rework this generator a little: we take one coil out and open the angle between the two from 120 to 180 degrees. What is now the vector sum of the two coil voltages? It happens to be 240V in a two-phase system with the two voltages 180 degrees apart.
Why 2:05 do you say the blue curve is lagging the red one? In every oscilloscope video I've seen, the first peak on the left LEADS the others.
You are correct, I added a note about it in the video description a couple of years ago.
DC is "out of phase"???
orientation does matter. now think about buck/boost.
In a split-phase (i.e. single-phase three-wire) system, the L1-N voltage lags (or leads) the L2-N voltage by 180 degrees, simply because you’re measuring both voltages with respect to the center tap.
If you measure L1-N and N-L2, then you get both are in phase, as expected. This is what happens when you place two AA batteries in series.
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3:20 Incorrect, the three windings are not 120 mechanical degrees (120 degrees in space) apart, they’re much, much closer to reduce harmonics.
In the interest of simplicity my explanation assumed a 2-pole generator hence the comment about 120 mechanical degrees. But most generators are not 2-pole, so yes the windings for most generators will be closer to each other than 120 degrees.
I don't understand you. For the single phase supply we are talking 180° out if phase between each line and neutral. You are going into semantics. Don't mislead viewers. Everything is relative.
*everything* isn't relative. *_Measurements_* are relative, but the polarity of induced voltage and direction of current flow are NOT relative, and are the *same* in both halves of the transformer. The way we take Measurements makes one half *appear* to have inverse polarity but in reality it is not. This video is about people using absolute terms to describe their relative Measurements. If you say "L1 *IS* 180 degrees out of phase with L2," then *YOU* are the one misleading people. It is only accurate to say "L1 *_APPEARS_*_ 180 degrees out of phase with L2 _*_when both are measured with respect to neutral."_* this is more than a semantic disagreement.
To the morons who keep insisting that the standard 120/240 volt Edison system is split phase. What would you call my 8,16,24 volt output on my chime transformer ? Maybe not split phase maybe 3 phase. Nope . Nice Fluke piece of test equipment. Just wish they could show where in an quality engineer book that ever says the 3 wire 120/240 single phase system can magically become split phase.Only split phase that I ever read about or worked on was on some AC motors feed from two wire as single phase and had either a capacitor in series with a start winding and some without a capacitor but a start winding.that was out of phase thus giving these motors the term split phase motors.
I understand and agree with the premise of your argument. Adding a tap to a transformer does not add a phase (an additional EM wave). I've seen transformers with as many as 12 outputs on the secondary. That was not a 12 phase transformer, it was a single phase transformer with 12 outputs.
That said, I think your understanding of the usage of "split" in this context is different than everyone else's. On that transformer with 12 outputs, the secondary is *split* 11 times (and if you unwind it you'll find that it literally is *split* as the term implies). The usage of the term "split phase" power for residential mains is very much preferred in my book, considering the alternative is *two phase* which is borderline blasphemy.
If you want to find the term "split phase" in an EE textbook, check out this citation from the Wikipedia page on split phase (I haven't read the book myself): Terrell Croft and Wilford Summers (ed), American Electricians' Handbook, Eleventh Edition, McGraw Hill, New York (1987) ISBN 0-07-013932-6, chapter 3, pages 3-10, 3-14 to 3-22.
The "split phase" i believe you referring to with regard to motors is the PSC (permanent split capacitor) motor. And it's a good thing you brought up motors, because the capacitors in single phase motors (as opposed to taps in transformers) *actually do* create new phases, with measurable phase angle difference from the original.
You are creating unnecessary confusion. Apparently your o'scope has floating probes inputs that can be connected anywhere. You are connected the probe "ground" lead to hot wires. Most scopes would end up with fired probes if you did that. Normally all your probe ground leads have to connect to a grounded or neutral reference point. When connected this way you will obviously see two waveforms of opposite polarity - i.e. 180 deg out of phase. To get the total voltage between two wires, you subtract one from the other. So it's 120 volts minus negative 120 volts. which equals 240 volts. This is a valid understanding. No need to confuse people by claiming it's not true.
The same is true if you had a DC power supply with a +12 volt output and a -12 volt output, both referenced to a "common" terminal. You wouldn't tell people it's not really a -12 volt terminal. That's the way most people would understand it. The voltage between the two terminals is +12 volts minus -12 volts. You can still think of it as two 12 volt supplies in series if you want. But don't say the other explanation is wrong.
I've seen this +120V minus (-120V) argument before and I don't understand where it comes from. Why are we subtracting? Shouldn't we be adding? In what other scenarios do you subtract? And how do you know when you're in a subtracting scenario?
"You can think of it as two supplies in series if you want" ... is there any more valid way to think of it? That's exactly what it is. You brought up dual 12VDC supplies and I would like to further that analogy. Let's say your DC supplies are batteries, and there isn't two of them, there's six. It's a series string, all same polarity, let's say for a high voltage golf cart. But we don't know that yet. We look at it and see that there are 6 batteries, each marked 12V, and when we measure from one end to the other end with a DMM we get 72V. That right there tells you the entire circuit, even if you can't see how the wires are routed. There is only one configuration of 12V batteries which yields that result: 6 batteries, all in series, all connected with the same polarity. If one of them had opposite polarity from the rest, you would measure 48V, as the voltage from two of the batteries would cancel out. If two batteries had reversed polarity you would measure 24V. If three batteries were inverted, the entire pack would cancel out and you would read 0V. From the 72V measurement we know that the batteries can't be anything other than all in series, all same polarity. That would be true whether you were measuring from either end, or center to either end, whatever.
This would be true too, if there were only two batteries. And if they were 120V. And if they were AC instead of DC. And if they were transformer outputs instead of batteries.
Now I circle back to answer my original questions. We know that we are in a subtracting scenario when we know that we are *measuring* one of the series sources with opposite polarity from the other(s). That informed decision to invert the mathematical operation is to compensate for the known inversion of the measurement.
That's all fine and good if it's an informed decision and a known inversion. But in many (dare I say most?) cases, it isn't either of those - it's rote regurgitation of something they were told, and think they understand, but don't. You obviously get it but my experiences in discussing this with others indicate that most don't. They think L1 and L2 are literally inverted with respect to each other. These folks can talk at length on this topic, saying all the right things "conventional model" things and you'd never know that they actually have a completely different (and flawed) understanding from the one that you and I do. You only discover it by digging deeper, where you find that many think current flows opposite directions through the loads on L1 and L2. And further misunderstanding builds from there. I don't disagree with anything you said, apart from the bit about "causing unnecessary confusion." I think (and other comments seem to confirm) that seeing things demonstrated this way is eye opening for a lot of people. The conventional model and its double negatives are confusing. Lots of people find this one less so. I believe that people can be trusted with truths that challenge convention and the world won't descend into chaos. Otherwise this video wouldn't exist.
Apologies, but you know enough to be dangerous. 120V 3 phase, phase to ground or phase to phase is not the same as a household 120V split phase. Being amazed that different measurements give different results -> just do the math first... it's rather simple. Coming from a power electronics engineer that learned the actual facts about 40 yrs ago - facts don't change.
Apologies, but you watched just enough of the video to think you knew what it was about before commenting on how educated you are, how educated I'm not, and take shots at me over nothing specific. You contributed nothing of substance. Now you have the opportunity to do better. If you'd like to discuss some of these facts you learned 40 years ago, please feel free to pick something from the video that you think I got wrong, and set the record straight.
But once again, the important thing is the ground. A load applied across L1 and ground, only, will experience the opposite polarity, compared to the same load applied across L2 and ground, only.
This will be so, at all points in time, other than at crossover.
Therefore, the current in the load will flow the opposite direction, in the load!
If you think about it, it ALWAYs flows in opposite directions in L1 and L2, because at any point in time, if L1 is positive going, then L2 is negative going, so current will be going towards the source on one while coming from it on the other.
What changes, with split phase, is where the current goes.
When you have the center tap, regardless of ground tie, some of the current goes through that, meaning the two ends are no longer necessarily balanced and are instead determined by the loads applied.
In an ideal world, for maximum efficiency, you should balance the loads perfectly, making the center tap current zero, but this isn’t practical and I suspect that’s partly why the practice is not done on this side of the Atlantic. Over here we don’t like generating power that doesn’t get used, so we use the full wave 240v. (Actually standardised 230v, nowadays)
But it’s really important that people understand that, while accidentally coming in contact with either L1, or L2 while standing barefoot will probably not be a fatal event, both at the same time most likely will, especially if wearing insulated safety footwear.
Videos like yours blur that, for regular folk.
My video doesn't blur that, it refutes it. Current does *not* flow opposite directions through the loads on L1 and L2. I made a separate video to demonstrate that. It is short and sweet unlike this video:
ruclips.net/video/3PHjZOdqs1U/видео.html
Imagine nothing is connected to your breaker panel. You install one two-pole breaker. To that breaker you connect two 100ohm resistive loads in series across the 240V. Does current flow opposite directions through the two resistors? It shouldn't. It can't. Current can't flow two two directions at the same time in the same series circuit.
Now at the node between the two resistors you make a connection to neutral. Does anything change? It shouldn't. No current should flow in the neutral since the loads are balanced. And adding the neutral connection does not (can not possibly) cause any polarity inversion or phase shift. The current flows the *same* direction through the loads on L1 and the loads on L2. Current flows the *same* direction through both halves of secondary of the pole transformer, and voltage is induced across both halves of the secondary with the *same* polarity.
The only reason why it appears opposite polarity/180 degrees out of phase on the scope is because the scope measures one half of the secondary with opposite polarity as the other half. It is an *apparent* inversion, not a real one. And I think it is important that the less experienced folk learn this *fact* early on so they don't develop lifelong fundamental misunderstanding.
You are so confused and wrong. Yes, you measure voltages with respect to a reference. When the center tap is tied to ground as the reference, one of the "split phases" is -120V wrt ground, and the other phase is +120V wrt ground. So half of the coil of the secondary is below ground, and the other half of the coil is above ground. And what's the total difference between the two outer legs? 240V. But that's not 240V wrt ground, that's 240V wrt to the one end of the coil of the transformer. If you tie the center tap of the transformer to ground and call that the reference, then one side is +120V and the other side is -120V with respect to ground. But if you ignore the center tap and tie one end of the coil to ground and call that the reference, then the other end of the coil will go between +240V and -240V. The only one that's "confused about ground referenced measurements" is you!
I agree with everything you said here (except the part about me confused about ground referenced measurements) and I'm not sure how I managed not to convey any of that (to you) at least once in the video. Thank you for reiterating the content of my own video to me in a condescending didactic tone.
Your audio is out of phase with your video. :).
What a waste of time! The first thing you did was to correctly produce two sine waves 180 degrees out of phase. The rest was useless. You must be one of those PITA people at parties.
I'll take that as a nod of respect from someone who calls themselves "Fascist Pedant."
Okay I grant you that, but it’s not a practical point.
Truly isolated supplies are rare and vulnerable humans are almost always connected to ground.
Therefore, using ground as the common reference remains the safest option and treating the “hot” wires as separate phases is a valid, safe premise
One thing I've learned in the 2 years since I posted this video is that the word "phase" is dangerous. It means different things to different people, and it is rarely obvious what definition a person subscribes to as you discuss the matter. It is possible (common, even) to go through several pages of discussion with both sides thinking they're addressing apples with apples when in fact one side is talking oranges. I don't know definition you subscribe to, but per the one I do, I can't agree that single phase power is two phases.
I do agree however that isolated supplies are rare, isolated scopes even more rare, and ground is the safest reference point for anyone, especially those in the early stages of learning. I didn't mean to encourage non-ground-referenced voltage measurements, but only to demonstrate what they look like since I'm in a position to do so. If one never steps outside the mental realm of circuit analysis then my experiment probably seems of little to no (or negative) value. But for someone who spends most of their time in the measurement realm (the real world), the answers from the circuit analysis realm don't hold up. I hope my video illustrates why.
you cannot just choose your reference points willy nilly my friend. They are 180 degrees out of Phase when measured from the same point of reference. This is the same for the actual flow of the current. If they are flowing with respect to the same reference (the neutral) then they are in fact out of Phase so spin it how ever you want but the apples are still apples!!!
You should get a job in marketing and leave expensive industrial control alone!
Yes, you *can* choose your references willy nilly. Voltage is a differential measurement just like distance. It has a "point A" and a "point B" and as long as you state those two points it's a valid measurement. You obviously understand that as you said "when measured from the same reference point of reference" so I find your next statement puzzling:
"This is the same for the actual flow of current" - you honestly think current is flowing two directions simultaneously within the same coil of the transformer secondary? Please explain.
The measurement of phase should be taken from a common point. By reversing your reference on one of the phases, of course you can show them as being in phase. If you have two lines "in phase" and of the same electrical potential to their reference point, you will measure zero potential difference between them and you will be able to connect them together to increase the current supplied. If you have two lines which are 180 degrees out of phase according to their common reference point, you will measure double the potential difference between them and connecting them together would create a high current short circuit. Your hypothesis is wrong!
The measurement of *phase* should be taken between two separate *phases.*
Single phase is *SINGLE* phase. No valid measurement of phase shift is possible.
Take an isolation transformer with no center tap; current is flowing the same direction through, and voltage is induced with the same polarity across, each and every turn of that winding. Agree?
Now identify the very center turn of transformer, scratch the enamel off it, and solder a wire on. Did you magically invert the polarity of half of the winding? No you did not. Connect that center wire to an earth rod and call it "neutral." NOW did you magically invert half the winding? No you did not.
You just created a split phase transformer exactly the same as pole transformer and the two halves of it are *NOT* inverted with respect to each other, nor are they out of phase. They can't be out of phase because *they are the same phase.* On the scope you're just looking at two halves of the same wave and one half *appears* inverted from the other half because it's being measured with inverse polarity from the other half.
Misleading reference to ground the two legs are 180 degrees out of phase. If they were in phase, it would be 0 across them not 240
False. As I demonstrated repeatedly, if they were 180 degrees out of phase they would add to zero. Just like there would be 0V between (+) and (+) on two batteries that are connected from (-) to (-). The only way you get two 12V batteries to add up to 24V is if you connect them [(-)...(+)][(-)...(+)]. That is to say, *same* polarity, or in the terms some people use, *same* phase. Same goes for AC.
Audio is not synced.
At 2:59 that "blue" wave is LEADING the red wave not lagging.
You are correct. I made that correction in the comments when I posted it. Wasn't sure how to correct it on the video.
It has been said by others but probably needs to be said again: If the supply is single phase there can be no "out of phase".
Agreed. But you try telling some people that and and you'll realize the concept behind the word "phase" is not the same for everyone. It seems that people who go to college for Electronics Engineering, come away with an understanding of phase that is purely mathematical and they have no qualms about discussing "both phases" of that single phase source, and they back up their arguments with phasor trig. You don't even need need to break out the higher maths though. If you measure the length of a stick from the center outwards, it will require two separate measurements in opposite directions. It doesn't mean there are two sticks with opposite lengths, even if mathematical proofs can be interpreted that way.
Lots of bullshit. Phase measurements are referenced to neutral. He only proved that he can flip the scope probes and lie abot the phase.
*Phase* measurements are referenced to *another phase* . This is *single* phase power. There is no such thing as a valid phase measurement of single phase, unless you're comparing current to voltage in the same phase.
If you have a transformer with no center tap, is the voltage across the primary out of phase with itself? No. If you scratch the enamel off the center winding does that change? No. If you solder a wire onto that center winding, does that change? No. If you connect that wire to earth and call it "neutral" does that change? No. If you start taking all your measurements with reference to the new neutral, does that change? No. It will look that way on your scope, but your decision to call it neutral does not cause any magical inversion or phase shift.
When you're looking at L1 and L2 on a scope, you're looking at two halves of the *same wave* and that wave *can not* be out of phase with *itself.* It only appears that way because you're measuring one half of the wave with opposite probe polarity from the way you measuring the other half. What I proved was that if you change your probe polarity to match the transformer's polarity, you see what is actually going on. I lied about nothing.
That is why there are phasing dot markings on transformers for proper installation or applications.
Yes sir
They are in-phase otherwise the neutral would need to be much larger to handle 2x the current.
Great video , thanks! I also thought that L1 and L2 hot wires in an electrical panel are 180 degrees out of phase with each other. You cleared it all up nicely! But can you please explain how is it that when you have a balanced load on L1 and L2, meaning that L1 and L2 have the same amperage flowing through them, lets say 5 amps respectively, the current through the Neutral line is zero? What causes this cancellation of current flowing through the Neutral line? Why does not the Neutral line show 10 amps?
Would this suggest that while the voltages between L1 and L2 are in phase the current between the 2 lines are out of phase? Which somehow does not make sense.
imagine you have two 9 volt batteries connect in seris + - + - and across the two, you get 18v. Now you hook two 9v light bulbs in series. The voltage drop across the two loads has to equal the supply of 18v, so across the first load you get a drop of 9v, at this point, you would have 0 volts between the spot between the two light bulbs and the point between the two 9v batteries. So, now we have this wire connected between the two light bulbs connected also between the two batteries and that's our "neutral". Now disconnect one bulb; what happens? The other bulb remains on, and the "neutral" forms the circuit for a single battery and bulb.
The fact that L1 L2 are 180 deg out of phase is what allows the cancellation of current in the neutral, this video is misleading and the conclusions are wrong.
As a retired electrical engineer I just had to say something,That's because this guy is just adding confusion to the hole thing by saying that it's not 180 degrees out of phase, because it is 180 degrees out of phase. It's a matter of where it's referenced too, single phase distribution transformers have two 120 volt windings that are normally connected in series, which forms a 240 volt winding, center tapped.
Here in north America the center tapp is always connected to ground thus farming what everyone refers to as split phase, which from the point of view of the neutral or current carrying ground, and the actual Earth ground non-current carrying ground. The two 120 volt leggs are most definitely 180 degrees out of phase, for if they weren't, as he demonstrated in his confusing video there would be zero volts between the two hot legs, and because there 180 degrees out of phase is why when there's an equal load on each leg, the neutral is at zero current, and if the loads are not equal, then only the deference current appears on the neutral, because it's actually two loads in series across a 240 volt winding, which is why you never want to lift a neutral on a live panel because if you have a large deference between the two loads let's say in terms of resistance and ohms, one load has a resistance of 10 ohm's and the other is only 1 ohm, the 10 ohm load will have 9 times as much voltage across it as the 1 ohm load or 216 volts while the 1 ohm load only has 24 volts across it, how ever if both loads are equal in resistance and you lift or disconnect the neutral absolutely nothing happens. I hope this clears up some of the confusion!
@@maynardr6 Excellent explanation, good job!!
@@Brokendiode This guy is showing you that your premise is incorrect but you will not accept the truth. Let’s think of one branch circuit. It is a two pole 15 amp breaker so you would have 240 volts from L1 to L2. Correct? So, let’s take a #14 black from L1 to a 1200watt quarts lamp. And from the other side of the lamp white to the neutral bar. Now the lamp will work at 120 volts and be using 10 amperes. Correct? Ok, now let’s take another 1200 watt lamp and connect it to the same point on the white and run a red #14 back to the breaker on L2. Now you have another 120 volt lamp and 10 amps. Correct? If you agree so far great. Now turn of the breaker, cut the white wire next to the two lamps and turn the power back on. What happens? Will either lamp light up? Will they both burn out because you now have 240 volts going out. There is no 120 volts coming out of the breaker because no neutral. The answer is they will both work perfectly because the two 1200 watt lamps are in series on 240 volts.
Sound's out of sync on this video.
Thank you
On a 240v single phase generator motor how far are the 4 field winding poles from one another in degrees?
90 degrees
Dave Gordon also has a video on the same subject which may be even clearer.
Yep it's a great video. If it had been on RUclips first I wouldn't have made this one.
excellent! complete!
Good video bro, I think the term phase has to do with how the voltage rise & it's direction on each line really.
So L1 & L2 are hot L3 low side that is shared, center tapped.
Good point you make thou, it's like ,2 generators in one, two different 120 volts supply line.
Thank you. You explained in a smart way and helped me to clarify the dot from the transformer. Nothing works better than the power of example.
Is the blue lagging the red or is the red leading the blue?
See correction in video description
Great video!
OPEN UP YOUR MOUTH AND SPEAK I CANNOT HEAR YOU
IS THIS BETTER?
When they are in phase they add! Its not split phase its a multi transformer. This has confused me in learning the difference between US 240 and EU 230. I feel like people act like they are different but they aren't its just one sine wave, its not adding two waves together. 240 is simply two legs of a 3pole multi step down transformer where the middle between half the windings is tied to ground instead of one of the ends thats why its split voltage its not truly split phase and I feel that term needs to die off. I wonder if that was from a lack of understanding in the past.
I finally understand how US 240 actually works vs what everyone seems to say. Secondly when everyone talks about getting the neutral in a split voltage transformer why they act like you couldn't just neutral one of the other legs. From my understanding of a transformer it doesn't actually have a neutral in the first place its a leg on a transformer. If neutral wasn't tied to ground at all it would just be a phase. The only reason its not "live" is cause of how its all wired to ground and electricity takes the path of least resistance. Or is there something more Im not seeing?
Sorry Pete I don't think I can properly answer your questions; I'm not very familiar with EU distribution systems. It's my understanding that your 230V single phase is actually one phase of 400V 3-phase system, which different than what we have. As far as I know you don't have any split phase in the EU. but I am probably wrong.
@@charlesstaton8104 Correct EU doesn’t use split. Delta to substation then star to home. 230/400 50hz. Heavy appliances use 400 like ovens but in most cases can be wired as 230 as the induction burners use the 230 side. They have a few options for how to wire and are wired directly to the panel in Sweden, Germany, and many others not sure all. Rural parts of Norway use delta to home and simply ground one of the phases to create a neutral. In some cases this possibly leaves some people with ungrounded neutral but pretty much everything that plugs in has to use a two pole “though cheap stuff isn’t always setup right, like some lamp switches” as there is no polarisation like the US, UK and AU. The Schuko plug allows you to plug in grounded plugs in either direction. And most plugs now have shutters in them like the UK ones. Granted Norway might have updated the older parts of the grid by now to the modern standard. This 400v 3phase to home does allow 3phase ev chargers to be installed into the home which is pretty cool. France however while using a polarised plug does not have a standard for wiring “so I’ve heard” so one still needs the two pole switches. Anyway thank you for the response.
Edit: also the lines along the street are house voltage which does make it easier to steal electricity as one does not need a bucket to convert to house voltage.
Sorry this was long I love learning / discussing the differences in these things.
You suggest that the term “split phase” is misleading and should be dropped, but we need a term for the North American system. I think “split phase” is convenient and appropriate. It is used for a transformer which takes a single phase from the 3-phase distribution network and produces two outputs of identical voltage but opposite polarity. What would you call it without using too many syllables?
“Path of least resistance” is incorrect. Electricity takes all paths, but more current flows in paths with lower resistance.
@@GH-oi2jf Well good points and thats true. After reconsideration I think the common interpretation of split phase is why I felt it was misleading. Since it is a split phase that actually does make complete sense. It's just that everything I read made it come off as misleading but I see my error in reason now.
Regardless no mater my opinions anyway the standards are set. That isn't about to change anytime soon.
Ya those isolated oscopes look pretty neat.
You do make a good point about test equipment polarity vs actually equipment polarity. It's important so you can accurate know how things are looking like. However it's still technically 180 degrees out of phase from the point of view of the center tap neutral of the transformer.
"From the point of view of the center tap neutral" is fine by me. If you're saying that then obviously you understand the concepts and you're taking care to use precise language. What I have a problem with is people saying they *are* out of phase without any stipulation about measurement reference and when you try to correct them with "they only *appear* out of phase because you're using the center tap as a reference" they double down on "no, they literally *ARE* out of phase." That's the notion this video was made to address.
@@charlesstaton8104 Yes, they are out of phase with respect to ground, because that's how the transformer has been set up - with the center tap tied to ground. When you measure across both "legs", you get 240V (with respect to the other leg), but yet you still only have +/-120V wrt ground. So you have 240V potential between both legs, but each leg is only at most 120V away from ground, but they are away from ground in the opposite direction at any given time - hence they are "out of phase" with eachother when compared to ground. So how does this not mean that 120V split phase is 180 degrees opposite phase on both legs? The fallacy you've committed here is you want to take the reference point as important when you talk about amplitude, but not the reference point as important when discussing phase. You have to use the same reference point in talking about both values, or you end up in the logical fallacy that you've fallen into.
@@gorak9000 the measurement that oscilloscopes take is (amplitude @ time). When I refer to being out of phase, I'm referring to the measurement taken by the oscilloscope, which as I just stated, is amplitude @ time. I didn't realize I was expected to call out both elements of the oscilloscope measurement and discuss them individually each time I say "phase." I thought it would be sufficient to just point at the scope. My bad. I will try to do better.
Correct. This is why you are allowed to use only one neutral if making two 120v circuits from 240v without up sizing the neutral. These are called Multi Wire Branch Circuits in the electrical trade. A common residential mistake (like my house was initially wired) is putting both circuits on a tandem circuit breaker not realizing a standard breaker slot is only one phase. That could be a fire hazard if the combined current exceeds the neutral wire capacity. IIRC, the 2014 NEC now requires circuit breaker handle ties on a MWBC. This was because if only one side is turned off, neutral current can still flow where it is not expected creating a maintenance shock hazard.
Excellent demo! The key is to stop thinking of 240V from this type of system as two combined phases, because it's a single phase. 120V is just using half the coil length, hence "split phase". Two halves of the same winding can't be out-of-phase with each other - it can't be out-of-phase with itself.
It would also help if people stopped calling L1 and L2 "phases". They are merely bars, and a bar or contact point by itself doesn't have a phase, only a signal/circuit has a phase.
It’s conceptual. If you look at L1 and L2 simultaneously with respect to the center tap, you see two patterns 180° out of phase. This was illustrated early in the demonstration. The entire secondary is single phase, and cannot be out of phase with itself, but when you look at one-half of the secondary upside-down, it is reversed relative to the other half, or, equivalently, out of phase.
@@GH-oi2jf - Exactly, "upside-down" being the stipulation. For years, that goofy convention has confused the hell out of people when they try to reconcile it with the what they know about out-of-phase waveforms cancelling out. It would be much simpler and clearer to first teach that the L1-N circuit and the N-L2 circuit are IN-phase, so it gets visualized correctly and jives with prior learning in trig and physics.
@@pterafirma - I’ve had trig and physics and I have two engineering degrees. In my opinion, it is sometimes useful and can help understanding to view L1 and L2 as being two opposing phases, particularly to someone who is familiar with the European 3-phase systems, but noy the North American system. It is just a matter of point of view. The mathematics are equivalent. This is much ado about nothing, in my opinion.
So the split phase transformer is receiving 240v to begin with? And then it gets split on the secondary?
I watched about 1 minute of Clough42s latest video and got irritated at also hearing the misconceptualized 180 degree out of phase explanation for about the 5 millionth time as well. I appreciated the sentiment and tone in your forum post linking to your video, and I share it. Misery loves company, I'm just glad you're here with me. 😆
The struggle is real my friend. Curious, which forum are you referring to? It took dozens of battles on various forums over a span of a decade to finally spur me into making this video. I believe the one that sent me over the edge was on TractorByNet.
I'm subscribed to his Channel and I love his content but I couldn't help myself. I posted this on his video (copy/pasted):
Center-tapped single phase residential mains does *not* have two legs 180 degrees out of phase from each other. It is a *single phase* supply so there is only a *single* wave. Since there is a center tap, that allows us to measure half of the *single* wave (from L1 to center/neutral) independently from the other half (from center/neutral to L2). Note the order in which I mentioned those: *L1 to N* and *N to L2* ... That minor detail is significant. Most oscilloscopes are ground referenced and you are therefore forced to measure from *N to L1* and from *N to L2* so you are measuring one half of the wave *backwards* from the way you are measuring the other half, so they *"APPEAR"* 180 degrees out of phase but they are *NOT* and cannot possibly be. A wave cannot be 180 degrees out of phase with *itself* . It is critical to keep in mind there is *only one wave* and the two traces on you scope are two halves of it.
A Rotary Phase Converter does not take two waves which are 180 degrees out of phase and turn it into 3 waves 120 degrees out of phase. It takes a *single* wave existing between two points, adds a 3rd point, and the result is the creation of two new waves between the original two points and the new 3rd point, and the 3 resultant waves are 120 degrees apart.
You can run a RPC from from a single phase 240V source which isn't center tapped and has no neutral. If there's no center tap, no neutral, no "180 degrees out of phase" legs and the RPC still works, then all this discussion about neutral and the 180 degrees out of phase waves was extraneous.
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You have no videos
@@charlesstaton8104 no. Go check out (Mongo Fix) he a good repair man. You good repair too
Doesn't "split phase" mean it is actually 1 - 240V phase, but the neutral is connected to the midpoint of the coil (and also grounded), giving 2 - 120V circuits that appear to be 180 degrees out of phase (you can still bridge the two hots or ends of the coil to get 240V)? There are lots of transformers, especially power supplies, that have more than one take off point on the secondary coil to produce different voltages.
If by "bridge the two hots" you mean "connect a load across both hots" and not "connect both hots together" then yes, I agree with everything you said there.
@@charlesstaton8104 Yes "connect a load across both hots". Connecting both together would be the same as shorting the whole transformer. Very bad.
@@Nonplused Yea, if the load is a short..
On a different note one could actually argue is single phase systems actually single phase if they have a center tap. Because really they could be used as single phase or a 2 phase system. I think the main point you got across is more the understanding what important about phase /polarity and how to take into account measuring for it properly in different types of systems. Very good video curious where you bought your variacator/ vfo equipment. Can it do nonlinear waveforms or just straight sinusoidal wave forms. Basically can it also be used as a full signal generator of any arbitrary wave form you want? And what frequency ranges can you generate with it at what current/voltage levels ?
Interesting argument about 2 phase, I don't think I could shoot it down without looking up some definitions but I can offer the fact that 2-phase systems do exist and they're basically 2 separate single phase systems that are 90 degrees out of phase with each other.
As far as my equipment, for the 3 phase i was using an American Rotary ADX30 rotary phase converter which turns 240 single phase into 240 3 phase, and that fed into a 3 phase transformer to get 480V 3 phase. That is good for about 20A @ 480V. The variac was just a single phase 1.5kW variac off Amazon capable of 0-130V with 110V input. Nothing I showed is capable of changing frequency or waveform, just transformers.
wow... single phase is single phase...
If the centre tap is grounded, it's obvious the opposite ends of the transformer would look like it's "out of phase", they are just mirroring each other in opposite directions...
A true 180° out of phase would be a generator with two or four phases, I don't even know if exists today, but in the early history I know they tested a different number of phases in generators.
There are some polyphase (>3 phase) motors used in the oil & gas industry I have seen, 6 phase and 9 phase, but these were powered by a special inverter and there was no generator outputting 6 or 9 phases. In the American northeast there are some areas that were electrified before much standardization had taken root, and they have two phase power. Basically two single phase supplies 90 degrees out of phase. This allows for a rotating magnetic field so motors didn't need start/run caps. This was/is inferior to the 3 phase we ended up standardizing on, since it also provides a rotating magnetic field but with only 3 wires.
@@charlesstaton8104 Very nice info, never heard of such things before. Thanks for this video btw. I have a deep respect for people who give their time for free to help teach others. Greetings from Brazil.
A sinusoid that experiences a 180 degree phase shift is mathematically identical to a sinusoid that is inverted (negative amplitude).
Agreed. And the two halves of a split phase transformer are neither phase shifted nor inverted.
@@charlesstaton8104 The end result is phase shift or inverted depending on how you look at it. Your video just demostrated that.
@@jptrainor my video demonstrated that the two halves of the single phase are in-phase and same polarity, but depending on how measure them, they may *appear* out of phase or inverted polarity.
Excellent explainer! Subscribed!
24:00, could you alternatively utilize an isolation transformer on the older scope?
With an isolation transformer powering the scope you could connect your probe's ground clip to L1 and directly measure the 240V waveform by probing L2 (or vise versa). But you could NOT clip probe 1 ground and L1 and probe 2 ground on neutral.
*NOTE.* using an isolation transformer as described is *DANGEROUS* as it will elevate the chassis of the scope and every metal part of the scope to the voltage of whatever your ground is clipped to. *If you touch the scope you will get a 120V shock* and if the scope is touching anything metal it can short out and blow up. *NOT RECOMMEND*
I have been using an old 2 ch Tek scope for decades. No problem. Hook up the scope’s reference to the white center tap and the two probes to red and black. You see the two phases - 180 degrees apart.
Thanks for taking the time to produce this video, Chuck. A couple weeks ago, I decided I was going to understand split phase power. And now I do. Now I can explain it to someone else. Either 120 leg is basically a shortcut circuit within the transformer and the 240 is the full circuit. Thanks again.
Hey, 4th term electrical apprentice here in Canada.
I think this cleared up a misconception I previously had when told our split phase system is 180 degrees out of phase; when I thought about it more it didn’t really make sense to me. So could I summarize your video by saying it’s really an issue of polarity when measuring from neutral/ground to either phase?
Also, could you recommend a video that describes how transformers supplying residences are actually connected? I’m not sure I fully understand what I previously believed I had a good grasp of. I don’t know if I fully grasp how current is travelling.
_"could I summarize your video by saying it’s really an issue of polarity when measuring from neutral/ground to either phase?"_
Yes. The vast majority of people on both sides of the debate are using the term "180 degrees out of phase" to mean "inverse polarity." I highly doubt anyone is arguing that L1 leads or lags L2 by 8.3333mS (1/60Hz/2). I've had this debate with at least 100 people and not one of them has made that argument. It's technically not wrong to say "180 degrees out of phase" as a 180 degree phase shift is indistinguishable from a polarity inversion for a sine wave (not the case for asymmetric waves like sawtooth) but it can be confusing. For that reason I've started saying "inverse polarity" instead of "180 degrees out of phase."
Here's an example I have been using recently: you have a 48V golf cart with six 8V batteries in series. You can look at it and see that they are all connected with same polarity ("in phase" - although that's a bit of a misuse of the term) and if you measure from one end of the series string to the other, you will see 48V, which could *only* happen if they were all connected same polarity. But if you measure from the midpoint between batteries 3 and 4, you'll see -24V, -16V, -8V, +8V, +16V, and +24V. Same thing for a center-tapped (split phase) transformer. The *apparent* polarity inversion is due *ONLY* to using the center tap as the reference point. One of your *MEASUREMENTS* has inverted polarity, but the *SOURCE does not.* Every one of the dozens or hundreds of turns of the secondary winding is induced with voltage of the same polarity, and current flows the same direction through every one of them.
_"Also, could you recommend a video that describes how transformers supplying residences are actually connected?"_
Check out Dave Gordon's videos. This one seems like it might address your question, although I haven't watched it.
ruclips.net/video/xMZkKI5rleg/видео.html
_"I’m not sure I fully understand what I previously believed I had a good grasp of."_
Dave Gordon is an actual educator and his videos are better than mine. If you have any lingering misunderstanding about the topic of my video, check out his video on the same topic, it's much easier to follow than mine:
ruclips.net/video/nOSYHUxHxG8/видео.html
_"I don’t know if I fully grasp how current is travelling."_
Current flows the same direction through the loads on L1 and the loads on L2. I have demonstrated this in another video:
ruclips.net/video/3PHjZOdqs1U/видео.html
@@charlesstaton8104 Thanks for your response, I really appreciate it! Originally came across this video via a forum you had posted it to, glad I did.
@@w0k_b936 I'm curious which forum? This is something I've posted on multiple forums
@@charlesstaton8104 It was an ‘All About Circuits” forum
This is all a waste of time. You do not have TWO independent isolated sources wit 4 wires that you can flip at your pleasure. The US split 120/240 system comes with 2 wires and the Neutral the phasing is already decided by the power company and is 180 degrees. Now, if you place an isolation transformer you can flip one of the phases but that is not whet the power company gives you.
I agree with every word of this (including the part about it being a waste of time) except for *"and it is 180 degrees."*
If you have a single phase transformer with no center tap, current flows the same direction, and voltage is induced with the same polarity, in every turn of the secondary. Every one of 100s or 1000s of turns is in-phase with every other turn. This does not change if you locate the center turn, scratch off the enamel, solder on a wire and attach it to earth ground, and call it neutral.
@@charlesstaton8104 Of course. The center tap is the END of the first half of the winding and the Beginning of the second half of the winding. Therefore by forcing the center tap to be the common point one has no other option than measure the two winding extremes dereferenced to the center tap. Ergo the resulting opposite phase relation. These is all basic and very clear to anyone that learns science without the desire to be controversial at all costs.
@@geppettocollodi8945 I agree that it is very basic and very clear to anyone who understands the science, yet people still insist that two halves of a winding are 180 degrees out of phase with each other when they obviously are not. This leads to confusion among the less informed and further misconception. Do you know how many people think that current flows opposite directions in the loads on L1 and the loads on L2? It's a lot of people, and it stems from this false "180 degrees out of phase" notion.
This is a philosophical debate really, like the old question "if a tree falls in the woods and nobody is there to hear it, is there any sound?" For some people, sound and voltage are human observations so a tree falling without an observer makes no sound and a voltage measurement IS TRUTH no matter the polarity. For others, sound and voltage are natural phenomena that exist independent from observation.
If you can take two ground-referenced measurements, knowing fully well that they are being taken with opposite polarity from one another and insist that the two voltages *ARE* opposing, with no caveat that it only appears that way because one of your measurements are backwards, then you're in the first camp. The philosophical camp. I'm in the realist camp. Those voltages are *NOT* opposing, they only *LOOK* that way because one of them is being measured backwards. From where I sit, *YOUR* camp is the one being controversial at all costs.
@@charlesstaton8104 Too stupid to bother debating. OO
I'm not sure exactly what point it is you are trying to make. What you are saying seems obvious. But I think a few misconceptions you may have are leading to misunderstanding.
First, you referred repeatedly to apparent and actual values. Apparent and actual negative values, apparent 180 degrees out of phase, apparent polarity reversal. Apparent is actual. What you are missing is that there is no absolute ground point. Ground in a circuit is simply the point you choose as a reference from which to compare other points in the circuit. Voltage is the difference in electric potential between two points. It can be any two points you choose. The only thing that determines whether the value will be positive or negative is which of the points you choose to put your black lead on, that is your reference point for that measurement. This is true for polarity and also for phase.
When we talk about two signals being out of phase, we mean the signals of interest. This is most often the output or input wave forms. In the case of residential electric supplied with 120/240V split phase service, the wave forms of interest are the two live or hot wires as referenced to neutral. The distribution transformer secondary winding is 240 volts between it's ends and is center tapped. The service drop is made up of a neutral line connected to the transformer's center tap and two lines connected to the ends of the winding which provide 120V with respect to the neutral line. As your demonstration shows, when you measure voltage from the center point of two batteries that are in series with the same polarity, one will read positive, the other negative. This is because your leads are "reversed" across one of the batteries so that the black lead is always at the center tap. It is important that we always measure the voltage from the same reference point within a given circuit, otherwise it is not very useful to us.
Since we are defining our reference point to be the neutral conductor, which is connected to the transformer center tap, one of the live lines will have the opposite polarity to the other. This means the wave forms of the signals measured from neutral to each live line will be 180 degrees out of phase. The point is, it is the reading we get based on where we define our ground or neutral reference, that makes it out of phase, not the configuration of the transformer windings.
I hope this helps to make this more clear and not less so. I would be happy if my EE education can help somebody else understand electricity, and I won't even leave you with a pile of student loan debt :-).
Wow, rarely does anyone disagree with this so respectfully. Thank you!
I understand your point about apparent=actual for voltage, as it is a differential measurement like distance, and valid between point A and point B. Aville is 240 miles north of Bville, and home is right in the middle between them. There is a single car driving back and forth between Aville and Bville. If you're standing in Aville or Bville, it will look like the car is driving 240 miles away and coming back, but from the perspective of home, it will look like the car is driving 120 miles away in one direction and then 120 miles away in the other. And it won't just *look* that way, it *will* be doing that, since the measurement isn't how far the car drives, but how far it drives *from you,* the reference point.
But I think it is important to have and maintain a concept of how far the car drives (not from you, but total) and what direction it's driving at any given time, because disregarding that data leads to fundamental confusion. I think most people see two cars in this exercise, which drive eternally in opposite directions, crossing precisely at home each time.
This misunderstanding leads to other ones. Many many people think current flows opposite directions through the loads on L1 and the loads on L2 as a result of treating the measurements this way. I can't tell you how many times I've had to address that.
When you're looking at L1 and L2 on a scope, you're looking at two halves of the same wave, current is flowing the same direction, and voltage is induced in the same direction. They have same polarity. One half of the wave can't be *actually* out of phase with the other half, because they're two halves of the same wave. You can make them look either way if you have an isolated scope; one way is more common and the other way is less confusing.
The above is the better wording of my argument as informed by two years of discussion in this comment section and elsewhere since making the video. I hope this helps clarify where I'm coming from with regard to "apparent" vs "actual."
@charlesstaton8104 Not having the two years of updated info is a hazard when responding to older videos. It is a failing of mine that I often fail to notice the age of the video. They are all new to me.
I haven't encountered anyone yet who was confused by the current direction, but then I am most often working with other engineers or electricians.
As to your first comment about being respectful, I try to always use that as my default setting. I respect anyone willing to have a discussion. If we disagree, it just means we have more to learn from each other. I can't understand why some people think you have to hate anyone who disagrees with you.
Anyway, best of luck with your channel, I hope you are successful in relieving people's confusion on this and other topics. There is much work to be done in that area.
@@jssamp4442 i don't know what it is about this topic in particular but it seems to bring out the worst in people, almost as if it were a political topic. I include myself in that; you may have noticed I had a certain "tone" or "attitude" in the video. That is because I recorded it in response to being beat about the neck and head over this in a forum. I had a bit of spite fueling me.
That was regrettable, and I plan to record a new video, a followup of sorts, where I replace that attitude with the better methods I've found to explain this in the past two years, along with an objective explanation of the counter argument. Sort of "when people who know what they're talking about, say that L1 is 180 degrees out of phase with L2, here's why they are saying it. They're not technically wrong but if you repeat what they say without understanding these key concepts, *you will* be."
I have heard the "current flows through L1 the opposite direction from L2" line from plenty of Engineers and Electricians. Recently I had a trio of Electronics Engineers with a combined >100 years of experience trying to force feed it to me on allaboutcircuits.com. I think if you did a little covert social experiment on your peers, find a way to organically get them talking about it, you might be surprised to find some of them believe this.
@@charlesstaton8104 LOL, you might be right about that last, but I don't want to lose my admiration for my profession. I think your approach to your new video is spot on. It can be so easy to put people on the defensive, and in that state it is nearly impossible for your message to get through. Another way to soften a critique that someone might otherwise get offended by is to use some version of FEEL, FELT, FOUND. "I know how you feel. I felt the same way. But then I found out..." It takes it from a lecture down to a word of mouth recommendation type of vibe. Of course it has to be authentic, something you really used to think but learned better or you might just come off as fake.
Somehow I have picked up a strange mish-mash of communication skills in my nearly 60 trips around the sun. I never thought of myself as a good speaker or a teacher but my students seemed to think I did well enough. I was more surprised by that than anybody else.
I look forward to seeing your new video when it comes out. I'll hit notify so I don't miss it.
Do some research on 2 phase in Philadelphia. It is actually still in use in some parts of the city. I have a milling machine and a lathe that both have 2 phase motors on them. I run them on a phase converter that was made in Philly. The motors have 8 wires instead of 9.
Yes I'm aware of it and have discussed it in other comments here, but intentionally didn't mention it in the video for fear of causing confusion. You're the first person I've ever "met" who actually has used the 2-phase stuff. I'm on a couple of machining forums and occasionally someone will pop up with a 2-phase machine tool asking for help. My suggestion has always been to upgrade to 3-phase, and since it's usually in a home shop, power it with a VFD. what's this phase converter? I've never heard of it. I know of the "Scott-T" transformer to turn 2-phase into 3phase and I know of the ubiquitous static and rotary converters which turn single phase into 3 phase but never heard of any kind of converter that turns anything into 2-phase. What's it called? Is it expensive? Does it require you to de-rate the motor and/or make the motor run hot? How does it work? Capacitors? Inductors? Rotary converter? Please explain. You've piqued my interest. Maybe your answers will change my boilerplate advice on the 2-phase motor dilemma.
Wow, I didn’t realize there was anywhere in the US that still has 2 phase. Thanks for that! There is a power distribution line out West that is still DC. I heard about it when in meetings with Electric Utility company about solar install plans.
@@charlesstaton8104 Sorry I didn't reply a year ago. The phase converter looks like a normal rotary phase converter. It has no start capacitors or relays in it, just run caps. I have run both machines on a vfd but never did any amperage measurements. It still remains a mystery to me.
@@KenPaisley haha! Better late than never. Thanks
it is a single transformer that is center tapped for 2 legs, therefore L1 to L2 is always the maximum voltage of 240 coming into the system, but when we need 2 legs of 120v each, there is only one way to do it, center tap! so both phases are out of phase in reference to the neutral(center tap) BUT if we do L1 to Neutral and Neutral to L2 then it is in-phase! but we don't draw the current that way in a split phase system, instead we have to do it with a common neutral so we go L1 to neutral and L2 to neutral! so they would be out of phase.
This is a great video for electrical geeks like us. For the overwhelming majority of non-engineering people out there, this is a distinction without a difference- the same argument as a single phase versus split phase system. I am a fan of using the correct terminology, but I find that mob mentality rules. I am in the solar industry, and it makes me cringe when I hear someone say "panel" instead of module. Two totally different things- one heats water, the other creates electricity. But the mob has decided there is no difference.
I really appreciate you doing this video. Apprentice Commercial Electrician about to Journey Out. This really put things into perspective compared to what the mainstream consensus is.
What happens if you measure both lines using the ground connector (coco) in the neutral connector?
This audio is 180 out of phase.
LOL can you expound on that? You're not the first to complain about the audio but most people don't have any issue. I think it might be a stereo/mono issue that only manifests on certain devices but I haven't been able to observe it on any devices I've played it on. Mind sharing what device you're using and what kind of speakers? Headphones? Mono/stereo if you know? Etc. I would like to get to the bottom of it and fix it if possible or at least not repeat the mistake on future videos.
@@charlesstaton8104 It just isn't synced. Sometimes I notice that while streaming a movie. Usually stopping and starting over fixes it, I didn't try it on your video however.
👍👍
They are 180 out of phase because they share a common wire. you could have measured it wrong in the 3 phase too - why did you put all the grounds together. If you put two separate devices in each 120 line they can receive any phase. But if you plug two devices that share common ground in each of the two 120V lines they there is only one way to connect them -the common ground goes to neutral and they receive two 180 deg out of phase signals. Now I know this doesn't happen too often... Here is another explanation. In a schematic you point all the positive voltages and the negative goes to ground. If you have also negatative power supply you could argue that it's not negative and it's positive when you measure the other way, but when you have a common wire you only talk about polarity on the other wires with respect to the common one. so the two lines are out of phase with respect to the common wire.
It's like negative voltage in DC power supplies, depends on how it's measured, -12-0-+12, could measure as 24v, or 12v with opposite polarity, and 12v,
Thanks for the demonstration. Center taped transformers are simple. They do divide voltage an AC voltage. It is rare for people have a reason to poke around in a panel with an oscilloscope. My battery powered scope has common grounds so i would never hook it up the way you can with the fully isolated channels on your scope. Using a low voltage transformer to illustrate was wise on your part.
Thanks for making this video. It explains well. It’s correct. It’s info that ought to be more widely understood.
It is just a matter of how you look at it. The two 120v lines of a split-phase system are equivalent to two 120v lines which are 180° out of phase, however they were generated. It is just a semantic argument, not a substantive one.
@@GH-oi2jf if you have a 240" long board you can measure it from end to end and get 240". But if your tape measure is nailed to the middle of the board then you have to take two measurements; from middle to end#1, and middle to end#2, and add them together. But what we do for the classroom explanation for this L1/L2 thing is tell students there are two sticks, one having a positive length and the other having a negative length, and instead of adding them together we subtract because 120-(-120) = 240. Why do we reach around the world to scratch our back when the *_actual_* explanation is much more intuitive, and much more accurate? It is not merely a semantic difference when it leaves people thinking there are literally two sticks (because that's just what we told them) and confused about whether single phase is actually single phase or if it's two-phase, and if it leaves them unable to explain why they're subtracting the measurements instead of adding them like they know they should be. If you know enough to call it semantics then you get what is really going on, but many people don't. This video is for them.
@@charlesstaton8104 Sorry sir, but I find you video confusing.
Now to be honest, I do no live in the US, so your strange two phase 180 degrees system is only for my curiosity.
In Norway we used a 3-phase 230 V IT-network distribution system from about 1920 up til about 1995. From 1995 most new areas are provided with a 3-phase 230/400V TN-system. This system are now the most common distribution system in the world.
@@kjellg6532 the US system is silly, so don't feel bad if you don't understand it. I am silly too, so don't feel bad if you don't understand me either. The US system for residential is just single phase. Imagine a small single phase transformer for making 24 volts, some devices use low voltage AC like that. Now add a center tap to the transformer. You can measure from center to one wire, 12V. And center to the other, 12V. One wire to the other, still 24V. Still single phase. Adding a center tap does not add a phase. That's what the video is about.
@@charlesstaton8104 Now, let’s have a look: en.wikipedia.org/wiki/Split-phase_electric_power#
This article states that we have two phases 180 degrees apart. In short, I agree in that. If you do not agree, please correct the Wikipedia article, everybody is free to add or correct a Wikipedia statement.
As for the US system. In most of the world, appliances are made for 230V AC. The 230/400V TN system are in use in the grater part of the world. What does one benefit from the US split phase? A lower voltage. Not so harmfull if you touch it, but at the cost of much more costly copper in your house wiring.
E.g.
You charge a Tesla EV with 11 kW
- in the US split phase system you need a 46A breaker and 10 mm2 wires
- in Norway with 230/400V TN, you need 3*16A and 2,5 mm2 wires
I do not see any benefits from using a split phase system. Do you?
@@charlesstaton8104 Another way of formulating this question:
Split phase, US mains distribution.
Let’s split one coil in half with a center tap (white). We connect a 2 channel oscilloscope with its common reference to the white center tap and the red probe to the live red wire.
We see a sine wave on the scope. From a start point of 0V at zero phase angle the voltage increases to 120V when the angle reaches pi/2 or 90° if you like. (We leave out the amplitude and rms for now)
If we connect the black probe to the scope’s second channel, we see a second sine curve on the screen. This curve will start at 0V and go negative. At pi/2 the voltage will reach negative 120V.
The red voltage can be described with: V1=120*sin(ωt). The black voltage goes negative and can be described with V2=120*sin(ωt + pi). We see that the two voltages are both sine and separated with a phase angle of pi radians or 180°.
If you measure across the two legs, it is single phase 240. Measuring to ground they are 180 degrees out of phase. Unless working with a straight 240-volt device the legs are opposites 180 degrees out. Measurements should be made to ground in a home. Don't confuse the less experienced.
Technically you are right but can be confusing to the less experienced.
Confusion of the less experienced is the whole reason I have such an issue with this; the whole reason I made the video. I struggled with this for a long time back when I was trying to wrap my head around AC fundamentals. People were insisting that the two legs *are* "180 degrees out of phase" or "opposite polarity" or "inverse" and I just could not make that make sense. The math said that if that were true, they should cancel out and yield zero volts. It took me a long time to realize that the reason I couldn't make sense of it is because what I was taught, and what keeps being repeated by people who know better, is wrong. It's fine in my book to think of them as being inverse or out of phase if that's how you were taught and/or that's how you've gotten used to thinking of it, so long as you know somewhere in the back of your mind that it only appears that way because of how we measure it. There are a lot of people who deny that "technically I am right" because they think the two legs *literally are* inverted from one another, and they defend that position with vigor. This video was meant primarily for those people. Secondarily it is for the less experienced. I just want to dispel the myth that the two legs are *actually* out of phase and encourage folks to recognize the importance of specifying your reference point (even if it's ground, even though it normally is ground) and when talking to the less experienced, maybe take the extra step of pointing out the effect of using the center tap as a reference (it makes one side *appear* inverted).
Thank you for making this video. Hopefully, your explanation will help others understand that the two legs are not out of phase. I’ve thought about making a video on this, but it would be more of a circuit diagram based explanation.