Losing or "Dropping" a Neutral on a 120/240V System
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- Опубликовано: 17 июн 2023
- Mitch explains and diagrams losing a neutral on a 120/240V system and uses a lab model to demonstrate the outcome(s). He then uses a digital multimeter to measure values within the circuit.
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We had this exact issue occur years ago when a neighbors tree trimmer was using a long pole to move the "drop" wires out of his way while working in an oak tree. Problems started when he did that as the squirrels that harbor in the tree chew the insulation off then rub their teeth on the wire, in this case, the neutral twisted wire/cable and it broke in half. We had no idea that happened and found all of the lights in the house were different in brightness etc. It was so weird because we would turn on one set of lights and another bank of lights would dim or brighten, very strange when several lights on one switch would do that and we knew right away something was very wrong. We called the power company, and they sent a truck over to look into the matter. They had to come back with a different truck to replace the drop wires from their transformer to our meter. When we returned home, we saw a note they had been there and then we noticed a burn smell inside the house. Looking into the matter we found a lot of appliances, stereo, TV, Microwave, Garage door openers, Dimmer switches, computers and so forth not working. Got an electrician to look it over and was told power was reversed meaning they sent power to the neutral which was determined to be the only way for those appliances to get damaged. Called and filed a claim with SCE which was denied as their crew said "they had no issues" during the replacement of the drop. We told them it all happened that same afternoon when they did their service, but they declined our $12,000 damage claim. We persisted and finally they assigned the claim to one of their in house adjusters who told us it was routine for SCE to decline these kinds of claims as many of them are unrelated to SCE and folks tend to see if they will pay. We told them that policy was disgusting and totally unfair to those who have valid claims. In the end, the adjuster paid for our damages which took us several weeks to determine what was damaged and what was not. We couldn't believe how many items were "fried", from electric shavers to refrigerators !
Interestingly enough, something very similar happened to the shop of the electrical contractor I worked for some thirty-plus years ago. He lost computers, printers, etc. I am sorry to hear about the difficulties you encountered. Thank you for commenting, and thanks for watching!
Great comments by the homeowner - understandingly the person making the comment is not an electrician. For me... rather than the 'professional electrician' they retained placing blame on the utility contractor I would rather point to the homeowner UNKNOWINGLY contributing to the overall damage by continuously 'trying things' to see if they worked. For example - the razor did not fail until the homeowner turned it ON - at which point it was basically exposed to 240v resulting in instant failure.
The TV (and similar) which are ON even when they are OFF - those probably failed immediately when the neutral was broken.
Point being - don't keep 'trying things'. If a few things are acting weird - stop and call the Utility for assistance - if you tell them you think you have an Open Neutral you will be moved to the top of the list.
IMO it is very unlikely the utility contractor energized the neutral. They do this 100's of times every month and the neutral is typically un-insulated anyway making it a far-reach that they would make that mistake somehow. These people are highly trained. This is basic Electricity 101 for those crews.
I'm not putting any blame whatsoever on the homeowner - my wife would do the same thing under the circumstance. She would call me AFTER she tried everything in the house. Lol
Great presentation and great comments.
@@Ekanselter Don't keep "trying things" Is spot on advice!. Somewhere in the comments here, I mentioned that very first thing I tell anyone who calls me with tales of lights going bright and dim or what sounds like strange voltage fluctuations is to unplug any appliance they want to keep. I also tell them to leave as much as the can off until I or someone else can take a look at the system.
Yep. That tends to happen when a 120 volt device receives 240 volts... ⚡️ 😬
RUclips needs more channels like this. Simple demonstration, quick, clear, and concise. Subscribed.
Thank you for watching and subscribing. I am a fan of simple.
+1
@@takingmeasure 😂😂
Excellent example of the issue of a failed neutral.
A few years ago, my 220v work shop supply service lost it's neutral. 6 (0) aluminum underground cable buried. Neutral somehow got a nick in it were it come out of the conduit below the meter base and made the turn from vertical to horizonal (90 deg bend). Over time just the neutral aluminum wire corroded (green crusties) and corroded completely into causing a failed neutral. This failure happened between a 200+ foot drop from the meter pole and the shop service panel. Shop had a seperate safety ground rod installed and wired to the service panel in the shop. (did not help!)
Needless to say, voltages went way high on one leg of the 220v service. Florescent lights in the shop went crazy, some would not come on, and others were extremely bright (high voltage). Worse part, I had several DeWalt 20v battery chargers plugged into a long wall mounted service strip, and all the DeWalt chargers went up in smoke.
I was lucky, the battery chargers were the only thing that was damaged.
I had to get a circuit "sniffer" aka tracer to locate the actual fault location since I could not dig up over 200 feet of service cable. We found the fault with the sniffer/pinger, and had to dig up the underground cable in that location only, then cut out the failed wire area and replace it.
A true leaning experience ($$$) for me! If I ever see an imbalance in light brightness again anywhere, I know exactly what to go check with my trusty Flute Voltmeter.
Thanks for posting and explaining what happens....should be required learning for all homeowners and others!
Sounds as though you got off fairly lucky. I am happy for that. I have seen this scenario inflict a lot of damage over the years. So much depends on what loads are involved and active at the time. Thank you for watching and commenting!
Great video! I've been a full-time home inspector for over 25 years, and I often find it difficult explaining electrical theory to my clients in a way that the average homeowner can understand. One of these problems is when I explain why the breaker panel must be balanced as closely as possible. This is a perfect example of a clear and conscise explanation . The problem was broken down and explained in a simple, clear, and easy to understand way. Great job, and thank you!
Thank you for watching and commenting. We try to keep things as simple as possible. We are in the process of making a supplemental video to this that will answer a few questions that have come up in the comments. Thanks again!
I'm an electronics engineer, trained at BU graduated in1973. But this guy teaches me real electronics, not just the math.
Thank you for watching!
Great video, simple, to the point with great demo. This explained the problem at a house I lived in some thirty years ago and two “Licensed Electricians” couldn’t fix before I moved out.
Thank you for making this video. In college I worked for a small business owner who got "some guy he knew" to wire his warehouse for a fraction what a real electrician would have charged. The guy wired all of the 120V fluorescent fixtures (two in series) to 240V using only two wires (no neutral _or_ ground). Or in other words he bonded all the neutrals together in the middle of the warehouse and let it float. Keep in mind the lights could all be individually switched! Yet whenever I try to relate this story on any kind of social media, I get people coming out of the woodwork to tell me 240V balanced lighting is a thing, and they ignore my attempts to explain why this variation on it is bad. (Frankly as an electronics engineer - not an electrician - I feel that for safety even in balanced situations this configuration should never be allowed, but I don't write the codes.) Now I can just link them to this video instead of wasting words on it.
Thank you for watching, and thanks for the comment. Series connection of 120-volt devices on 240-volt circuits is not acceptable by any standards. For starters it is a violation of 110.3 and 110.4 in the National Electrical Code. And that's just a starting point. Circuits sharing a common neutral is a thing, but the neutral cannot be switched. As a practice, most electricians no longer share neutrals on 120V branch circuits, though you can if a single breaker simultaneously disconnects all the hot (ungrounded) conductors associated with the shared neutral. Additionally, the integrity of the neutral must be maintained and not reliant upon connection through the devices (receptacles for example) for the circuits. At the feeder level, we share a common neutral all day long, but we never switch it. Thanks again for watching!
Used to work on mains supply faults here in the UK , where Protective Multiple Earthing ( PME) supplied many modern houses.
When we had a neutral fault on the main distribution cable which was 3 phase, the houses affected has various voltage issues, some had basically zero volts at the main fuse others on another phase could have the normal 230 volts boosted to 400 volts.
The reason they got 400volts was dependant on the size of the load on that other phase, the higher the load the greater the voltage appearing on the neutral conductor which was effectively now a phase conductor due to the break in the neutral to the substation .
Sometimes lots of damage other times next to nothing.
Thank your for your input. What you describe is what makes these problems so confusing. The connected loads keep changing the overall circuit behavior (voltage balance). It's difficult go "get the entire picture" when troubleshooting.
@@mitchellhegman2402 What I should have added to simplify the reason for increase in voltage due to the load, is simply because higher load also equals lower resistance , sometimes this could be one large kW load or many parallel smaller but equivalent load.
These faults were a pain to trace, you could not just start trace ing the fault while the supply was on, it was a mad rush to the local distribution substation, identify the circuit and drop supplies so everyone was put off to try to limit damage but unfortunately the damage occurs in milliseconds.
@@radiotowers1159Fortunately, some devices are more robust and survive the 73% overvolt for hours .
Very useful demo on floating neutral.
With love from India. So we should know that neutral is a balancer.
Thanks for watching. Although we strive to operate with loads balanced on a neutral, that often proves to be a moving target.
Had this situation on a place I moved into once.
One circuit had dim lights, the other bright, unless I turned the bathroom fan on - then it swapped.
Took the "electrician" (who I'm NOT impressed with in this case) several HOURS just to diagnose the situation - after I TOLD THEM what the issue was.
The good news is that I hadn't installed anything into those rooms yet, and the DID eventually track the situation down to a WIRE NUT tying the neutral wires together that had failed it's connection.
Don't get me started on the OTHER issues with that place (like the use of 2 INDOOR electrical panels OUTSIDE the home).
I wasn't there very long.
I am happy you didn't lose any valuable electronics in the mix. I have seen intermittent connections in a wire nut many times over the years. That always leads electricians to the debate on whether wires should be twisted together (or not) before applying the wire nut. Thank you for watching and commenting!
@@takingmeasure When I was an apprentice, the Master I trained under REFUSED to accept Wire Nuts for anything - due to the many issues with them corroding over the long term, or vibrating loose.
He was ALSO not a fan of splices, for the same reasons.
He would toss you out of the program ENTIRELY if you spliced or used a wire nut on ground wires more than once as that was an outright violation of the CODE (at least at the time).
Firm believer in "best practices at all times".
@@bricefleckenstein9666 Sounds a lot like some of my training!
Excellent! This video should be required training for young electricians.
Thanks a lot my entire house does this now I have a new project.
Poor electrical connections, improper grounding and bonding, and distribution equipment failure can lead to strange voltage imbalances. Some of this can damage wiring and any connected appliances and devices. When someone tells me they are experiencing strange voltage fluctuations, I always recommend shutting down anything they can. I also recommend getting help troubleshooting from a professional for those who are not in the trades.
Awesome explanation! Great use of a demonstration followed by the theory.
Thank you for watching and commenting. I am a visual and "hands on" learner. These labs help me.
My home developed a case of flickering lamps, some brighter, some dimmer. Also my cable TV and Internet service became quite intermittent. I measured my line voltages and when the loads were unbalanced one 120V leg dropped to 100V while the other 120V leg increased to 140V. In other words the neutral was at 20V rather than 0V. I used a 1200 Watt space heater to create an imbalance in load currents for testing. After getting the power company to send a lineman out to inspect and repair the connections at the utility pole, there is less than 1V on the neutral (relative to ground) when I test with the space heater. However, my Internet service was still very poor. The cable technician came out and discovered that about a two foot length of their coax drop cable was melted at the end up on the utility pole. My assumption is the unbalanced neutral current was flowing through the coax cable. Replacement of the coax restored proper Internet service. Fortunately I’ve had no other problems since.
Thanks for sharing your story. An interesting one at that! I am glad you were able to get the connections back in order before more serious imbalances caused great damage.
Last year went on a service call to a home built in the late 1970s, where a 50 inch smart TV, DVR, blu-ray player and stereo system went up in smoke after a 1500W electric fireplace had been running for an hour or so plugged into another receptacle. A backstab connection on an upstream receptacle had burned up, and it was a multiwire circuit for the living room/master bedroom and each receptacle along the wall alternating between L1 & L2. This expensive ordeal could have been avoided if the neutral on the receptacles were pigtailed such that removal or failure of the device will not break continuity of the neutral, this is actually an NEC requirement found in 300.13 (B)
My neighbor had a similar scenario about two years ago. I have seen a lot of issues with backstab connections (and shared neutrals). I pigtailed everything I box I opened while troubleshooting. Nice work in citing the Code! Good stuff. Thanks for sharing the story.
MWBC circuits should be excluded from a RFQ (Request for Quote) as should backstab cheapo receptacles.
When we moved into our 1970's house about 20 years ago I quickly noticed a few quirks with the electrical system, where lights on certain 120v circuits would get brighter or dimmer depending whether lights on different 120v circuits were on or off. I found a couple of issues;
1) All the light switches and outlets were connected by 'back-stabbing' the wire into a small hole in the switch/outlet. Over the years due to arcing, etc, the connections had become burnt. I replaced every one of them and secured all wires using the screws for better contact.
2) Tracing all the circuits I determined several light circuits shared a common neutral.
3) I decided to go to the sub-panel for lights and outlets, and tighten all the screws to both the individual breakers and also the neutral buss bar. As I was tightening the neutral buss screws, half of the buss bar fractured and fell to the floor! It clearly had been overheated for years!
Fortunately, I was able to locate a replacement buss bar at a local provider. Once replaced and secured, I had no further problems. Wheee!
Yikes. I am glad you jumped on the issues and fixed things before more serious problems developed. Good work! Thanks for watching the video. I appreciate you sharing the story.
Good open neutral video. It should be pointed out that open neutrals have caused home fires in electronic equipment and in particular Metal Oxide Varistor transient protection devices. These can burn in an open neutral event during to current limited overvoltage. Breakers won't trip, as there's no overcurrent.
This caused a rewriting of UL standards re these devices several decades ago.
In switch mode power supplies which I designed years ago, we had several fires caused by mains through diode bridge connected Electrolytic caps. The 200 volt rated caps were grossly overvoltaged by the open neutral. The side vent snap-in lytics failed safe and released only vapors and smoke on overvoltage tests. Then purchasing got a good deal on an "equivalent " cap from a different mfg. These had a top vent, and nobody noticed myself included. Then we had a few fires caused by our products. Fortunately no deaths.
In testing the failing caps we got the foil and flammable electrolyte to pop out of the top vent like a Flaming party favor. Didn't even blow the internal 3 Amp fuse!
Today small power supplies and large are universal input, 90 to 260 vac, and use 400 volt rated Electrolytic caps, so open neutral fire incidents have come way down I'm happy to say.
Thank you for the comment. I have seen a lot of strange and dangerous events caused by open neutrals over the years. I really appreciate your take on this. I find myself ever-thankful for UL standards an the constant quest to revise them as required.
Excellent demonstration
The worst possible example of a dropped neutral happened to my neighbor. The house settled such that the neutral pulled out near the meter. Long story short, they fried a bunch of appliances and the shielding on the cable TV wire melted the insulation.
I have seen dropped neutrals far too many times in my years as electrician. More often than not, at least one appliance or electronic device is smoked. Any time I get a call from someone telling me they are seeing lights acting up and apparent voltage fluctuations, I tell them to unplug any appliances and electronic devices until an electrician can evaluate, just in case it is a dropped neutral. Thank for watching.
@@mitchellhegman2402 There are symptoms to look for. One of them, is the voltage shooting to 132+V on the leg with minimal load. The voltage rises when a motor comes on, the same with the range on! The same house that had the bad neutral connection, had a hard-wired smoke alarm that wasn't working. I suspected the bad neutral being the cause, along with no lamps working in a wall light fixture in the downstairs bathroom. This was back in April and May of 2016.
that happend to one of my neighbors when a tree fell on the line and ripped the neutral off the pole but missed the other 2 wires
We get those as “lights going bright and dim”.
Squirrels love to chew the bare aluminum in the triplex coming to the house.
@@richardcranium3579 I have seen more than a few times when critters caused power quality problems!
Great lesson
Well done explaining
Thank you
Thank you. And thank you for watching!
Thanks Very nicely demonstrated and it demonstrates the principles . The challenge would be to find resistors that dont change their value with voltage changes and compare the results even if just to confirm Ohms law. Perhaps wire wound heater elements could be tried , but even they would change resistance with voltage. I can't think of any other types of resistors you could use that would be stable.
This is thought provoking as I wonder how Mr.Ohms proved his Ohms law if the resistor values wont hold still while you do tests on them, that throws you math around. Considering what equipment he must have had for making measurements I am amazed he got it done.
Thanks for the comment. I struggled with ideas for building this lab. Having loads with resistance values that change is a bit confusing, but in the end this is realistic. Also, I really like the visual of the lights going bright and dim.
Awesome lecture, I have had this issue various times and it does cause some weird issues
Thank you! And thanks for watching! Hopefully, you don't run into this too often.
Very well explained sir! I love your teaching style! You are absolutely right about the changing resistance(dynamic resistance) of the filaments in incandescent lights. That dynamic resistance is known as a positive temperature coefficient. What that basically means is that if you increase the temperature on the tungsten filament, you increase the resistance in the filament as opposed to a negative temperature coefficient which means as you increase the temperature on any other negative temperature coefficient material the resistance decreases in that material. Tungsten basically has a positive temperature coefficient. Positive or negative temperature coefficient materials are widely used in thermistor technology.
Thank you so much for the positive feedback. I really enjoy labs such as the one I presented here. Working with the dynamic resistance made this all the more fun for me. Finally, thank you for sharing your knowledge. The learning never stops!
@@takingmeasurebsolutely you are so very welcome. Thank you for the demonstration. I enjoy labs as well. As a sidenote, I was working with a three way switch configuration in my dining room the other day, and I detected a ghost voltage on my digital multi meter. I notice a lot of people have that issue detecting phantom, voltages. One of my suggestions in that scenario is to use the low impedance Function if the meter is equipped with one. I believe one of the causes of phantom voltages is running many live circuits through a narrow raceway in close proximity to one another. When One circuit is energized and the adjacent circuit is not it creates what’s called a capacitive effect which induces a phantom voltage in the non energized circuit.
The nice thing about the old wiggy voltage meters and analog Simpson meters is they were very low impedance and never picked up any kind of phantom voltages.
@@OSAS726 I am working on a video for ghost voltage. I hope to have it live here in a couple weeks. Thanks again!
@@takingmeasure Oh that’s awesome! I’m looking forward to seeing your video on that subject. I just subscribed to your channel this morning! Thank you sir for all the great content. My background is 34 years residential and commercial high voltage and electronics engineering. I love your teaching style!
very well done sir! great explanation for something that commonly happens in households - also, dropped leg is sometimes baffeling because 1/2 the house works lol (experienced 3ph up to medium voltage)
Thank you so much! And thank you for watching.
Thanks for the very informative video. This is scary.
I've been working with low power electronic equipment for many years.
I don't get involved with house wiring. I didn't realize the hazard in the neutral connection.
As with any wiring system, 120/240V systems are reliable and safe when installed and functioning as designed (per Code). But if "unusual" voltage events seem to be occurring on such systems, I always recommend shutting down what loads you can, not operating any switches, and calling a professional to troubleshoot as soon as possible. Thank you for watching and commenting.
We had an open neutral which caused intermittent problems for a while. Eventually our main water line started leaking (buried in the yard). When the city came to replace the copper pipe they disconnected the ground strap, which they said drew an arc. That blew up some appliances, as the earth ground was acting as our neutral return, and once interrupted, caused unbalanced voltages just as in this demo. It's also nearly certain that the grounding currents eroded the water pipe over several months causing the leak. We had connection problems at the pole before, but this time the utility didn't even want to send a guy up to take a look. Even the electrician that the city sent out didn't seem to understand floating neutral hazards. Frustrating to me, as I'm an electrical engineer.
All in all it was a $5k repair, which I had to eat.
Yours is the type of story am sorry to hear. Electricity will find a way to return to the source as best it can. The fact you would up with a $5k bill adds insult to injury, I expect. I appreciate that you shared the story with us. Thank you.
I've been a cable guy for 17+ years. Well the first 15 was on the Telco side, but it was still internet/TV/phone. Moved over to the coax side of things about 2 years ago and have seena handful of melted coax at either the ground block inside or the tap outside. I even had one create tiny sparks, especially on the cast iron plumbing stack. My big yellow field voltage detector didn't turn red when I tested it though.
On grounded systems , current imposed on the grounding system will hunt for any grounded path leading back to he source. In cases where a grounded conductors are bonded to the equipment grounding system beyond the service bonding connection something called objectional current is placed on all the grounding paths. It's circuit current that should be on the grounded or neutral conductor following equipment ground and electrode grounding paths back to the source. This may have accounted from some of what you saw. Lightning can also do weird stuff. Be careful out there. Thank you for sharing!
Had the neutral line drop off my house in an overnight storm. In winter. Woke up to a freezing house since (of course) the furnace was on the side of the panel that went high! UPS under my desk was also on that side and it went -boom-. But you know... a bunch of lamps nicely went dim in an effort to save power (sigh).
Sorry to hear about that. Dropping a neutral is usually pretty ugly. Thanks for watching.
Great explanation. My son lost his neutral between the pole and the house when the neutral line broke (cracked we didn't notice it). We got some weird, dynamic imbalances which gave very confusing readings at the box. Fortunately we shut down the main and called the utility company who ran all new from the pole. Nothing was damaged.
Good move on shutting down the main! I am glad you spared yourselves from bigger problems. Thank you for watching.
excellent video...
Thank you. And thanks for watching!
If you lose your neutral, the symptoms are pretty clear. When you have a WEAK neutral it can take longer to figure out and get repaired, and the symptoms are less predictable. Some of the current leaks to ground, and some of it crosses the neutral.
Agree. Intermittent issues are always difficult to find and repair.
@@takingmeasure The fact that I'm only sometimes crazy is driving my doctor nuts!
Very good video, thank you🫡
Thanks for watching. Troubleshooting a dropped neutral is difficult. The trick is remembering the voltage imbalances are always downstream of the open neutral. Knowing this, you at least have some kind of starting point.
@@mitchellhegman2402 I’m still in highschool but I’m think about becoming and electrician and these kinds of the videos are the best thanks for the advice
@@noah2067 I loved my work as an electrician. I hope to see you join us.
I was living in the upstairs apartment in a renovated carriage house back in college and suddenly after six months with no issues all kinds of strange electrical problems started happening, like turning on the electric oven would cause the downstairs front porch light to come on, or using an outlet in my bedroom would turn off my bathroom light but turn on the stairwell light regardless of the position of its switch. Neither myself or the owner could figure it out, and both times the utility company came they said there was no problem on their side. I lived that way for months and just figured out the combinations needed to turn on what I needed on.. Then, by chance, I moved my bed frame and realized my alarm clock cord had been squeezed under one of the legs, once freed everything went back to normal. 💡 I'm not sure if it was what you are describing, the cord in my case wasn't even three prong rather a simple two lead cord and the insulation wasn't even cut through if I remember correctly. Whatever the cause, it affected every circuit in my apartment in one peculiar way or another. It didn't damage anything that I know of, not even the alarm clock though I did toss it out.
That is an interesting one! I'm not certain of the exact dynamics in your case. Thank you for sharing. It gives me one to ponder a bit. Thank you for watching!
Well done! Thank you. For fun I would have used 240 VAC and be careful.
Thanks for watching! 240 volts would definitely make for a lively lab...
So the observed voltage shift due to the dropped neutral will always point to the neutral that is part of the power drop to the box? Or could this voltage shift be caused by one phase using the neutral “wire” (miswired) from a load that is fed from the other half of the phase (effectively tying the return from a top lamp to the return from a bottom lamp)?
If two loads or lamps were somehow connected in series by mis-wiring I would say "yes." Very thought provoking. Thanks for watching and commenting!
nice job.
You can always tell when someone has dropped the neutral by the smell ha ha ! Aka don't let the smoke out !
No kidding on that! I have seen a few "smoked" appliances over the years. If someone calls me and describes weird voltage behavior, the first thing I tell them is to unplug any appliance or electronic equipment they are fond of. Thank you for the visit and comment!
Thanks Man!
Thanks for watching!
here nz we are a poly phase MEN system so what you were saying was of some interest
Thank you for watching!
@@takingmeasure a loop test would show up a fault here plus current readings on the neural and earth conductors
@@robertedwards3147 Yes.
If the three phase source and neutral loost what hapens for the lightstreet
Does it work for putting two DC/AC 120v pure sinewave inverters and create 240 if I combine Neutral and use two hot legs ?
That may be above my skillset. It's an interesting thought, but I am not sure.
yep. sure am glad we just stick to the 240 circuit and none of this split phase 120 nonsense...
I knew this was going to be good when I spotted the blueprint background.
Haha. I appreciate that! Thank for watching.
After a house fire my wife and I were staying in a camper trailer. It had a small freestanding refrigerator. My wife called me at work and told me the fridge was hopping up and down. I said to her I don’t know what you are talking about it cannot do that. I told her to unplug it. When I came home I plugged it in and it started to jump about. that thing weighed at least 60 pounds. After some investigation it turned out that the neutral wire in the incoming triplex had broken.Therefore no ground. I was told the voltage was hopping between 220 and zero.Hence there was enough energy to literally make it jump up and down. thankfully after a quick fix nothing had been harmed.
Wow! That is one of the most interesting stories I have heard. You are fortunate more damage did not result! Thank you for sharing that with is.
Not 100% sure but I think this is what happened in a neighbourhood in my country (The Netherlands). A neighbourhood had problems with regular power outages in one week, and the power company decided to replace the substation transformer of the neighbourhood ring, but might have forgotten the neutral or connected it wrong.
People experienced sparking outlets, devices starting to smoke badly, and in some cases also wiring that melted.
(Just read up on some of the new information before placing this: there's now also a suggestion that the leakage-detection device was connected without disconnecting the customers connected to said line, so the pulsing high voltage device meant to cause an audible spark so engineers can locate the fault underground (hopefully).
Since most homes have a 3-phase connection in the Netherlands with each phase at 240V (not in a split-phase setup), there was now a situation in which lower current drawing phases became part of the return path, and it caused weird voltages everywhere (and it's a thing warned for during the training for becoming an electrician because of how dangerous this can be in 3-phase setups).
The board reminded me a bit of the board a neighbour from my grandma made for me and my brother once.
Not a great situation for your neighbourhood. Sounds like something similar but on a larger scale. Definitely a mis-wired scheme of some sort. I appreciate the comment and thank you for watching.
The board reminds me of one used during training to demonstrate the unusually high neutral current caused by 3rd harmonics from fluorescent tubes, even if perfectly balanced . As this was serious training, the board used actual 3 phase mains and lights, not lower equivalents, a technique only taught in the distribution course as a way to test statewide effects .
@@johndododoe1411 That board would be super interesting to see! I love lessons that are realistic. Thank you for the comment.
In a properly grounded system i.e the panel is grounded and the pole transformer center tap is grounded - seeing as the neutral is the same as ground (connected together in the panel) - wouldn't the ground substitute for the neutral when the neutral disappears? - at least to a great degree?
In your panel board demonstration it would be the equivalent of a (green) wire from the neutral connections on the right side of the switch back to the common connection of the transformers on the left side of the switch - effectively bypassing the switch???
So if the neutral fails you still have the ground so the effect may not be so great?
You are correct. In a properly grounded and bonded system the equipment ground would be in place. But the ground wire only carries current when an ungrounded conductor or associated circuit parts is somehow connected to it. In this case, we opened a grounded conductor. The equipment ground still remains isolated. But it is there to protect from a ground fault if one should occur. Thank you for watching. I appreciate the comment!
@@takingmeasureAh yes, the grounded/grounding terminology that confuses casual listeners . Hence the clearer Neutral/Earth terminology used globally .
Ok, I apparently dodged a lethal bullet with my experience vs these stories. Lost a lamp and a couple APC power strips with (deadded now, no doubt) some form of protection circuitry.
Threw out the bits that lost their magic smoke and moved on, while cursing the installer.
You may well have been a bit lucky. I have heard a lot of stories of computers and expensive appliances going up in smoke. Thank you for watching and commenting.
@@takingmeasure It would appear so. I was told it was a "floating neutral" basically over time, the sheathing covering the end of the neutral wire had i suppose burnt away and revealed enough exposed surface to short? it was a rental so the electrical guy did the panel properly and that was that. but it sounded like negligence in the original wiring? that neutral maybe wasnt ever hooked up properly? I'm still trying to wrap my head around phasing etc. Love the content
Wouldn't it trigger RCD if each side had its own (not common like here) neutral and RCD?
If each side had it's own neutral the loss of one or the other would cause a loss of power to whichever side experiences the open circuit and not impact the other, if I am following here.
How did you get 53 vac under the lost neutral and lamp scenario? The power supply is 52 vac.
The transformers measure a higher voltage until they are put under a heavier load. Additionally, the voltage where we produce the videos typically measures above 120 volts. Given that we have a higher primary voltage (122ish) and relatively modest load, our secondary voltage runs a bit high. Fully loaded, power losses would likely see the measured voltage fall slightly below the rated (nominal) voltage. As it turned out for this lab, when the current dropped slightly after the light was switched out, the transformer losses were reduced enough to allow a slight increase in voltage. We are in the process making of a follow-up video to this one in which I try to address this and other question that have cropped up. I hope this helped answer your question. Thank you for watching.
Can someone explain to me how the circuit still powers the lights when the main shared neutral is open? Doesn’t it need a return to the source to operate properly? Thanks
When the neutral opens upstream of the loads, the current returning on neutrals on the top half of the drawing will begin flowing through the neutrals on the bottom half, through the bottom loads, and back to the source on the other ungrounded wire.. This places the top loads in series with the bottom loads and sees the full voltage (240V) dropped across them as a whole.
When the loads are perfectly balanced, the neutral does not need to carry any current back to the transformer. Current flows from the top "hot" leg, through the equal loads, and through the bottom "hot" leg. It works as if the balanced 120-volt loads combine to represent a single 240-volt load.
When the currents through the two hot legs are not perfectly balanced, however, the neutral from the transformer will carry the unbalanced portion of the current. If one hot leg is supplying 20 amps and the other hot leg is supplying 30 amps, the neutral wire from the transformer will be carrying only 10 amps.
@@peteduncan921 Well said!
Is this what's known as an Edison circuit? Great video
I have heard of them referred to as such on occasion. Thanks for watching!
How did the loads change impedance exactly when the neutral dropped?
Thanks for watching. In this circuit, when the neutral connection is lost, the top three lights are combined in parallel, resulting in a single resistance value. Similarly, the bottom three lights are also combined in parallel, forming a different resistance value. These parallel loads are then connected together at the neutral point, creating two equivalent loads in series.
When the resistance values of the loads on the top and bottom are matched or balanced, the voltage drop across each load is also balanced. However, if one of the lights in the bottom section is switched off, it disrupts the balance. Since the bottom three lights are connected in parallel, the removal of one light increases the overall resistance for that section of the circuit. As a result, more voltage is now dropped across the remaining two lights in the bottom section.
No doubt the bottom changed. How did the top as it is still the same 3 in parallel. With no change pre and post neutral drop, the effective R value cannot change
@@SeanONeill13 The ohmic values for the bulbs in the entire circuit changed because the actual resistance for incandescent bulbs changes any time the voltage (and current) is altered. As you may recall from the beginning of the lab, I only measured 26 ohms when the lamps were cold. Full resistance occurs when the rated voltage and expected current is applied (120V/0.333A = 360 ohms). As mentioned in the video, I had to use current and measured voltage values to determine the "R" values because they change with the other circuit variables (and heat). It's weird stuff.
I guess this would be a USA only problem, right?
We don't have such problems in our fully 230v home circuits here in Europe.
As I understand you systems, I believe that is correct.
How to calculate each phase voltage when loose neutral when unbalance load.
To calculate the voltage dropped across any point, you need to know the total series resistance of the circuit path as a starting point. Using that, you can calculate total current. Using ohms law, you can apply that to the resistance of each side (E = I x R) to determine the voltage drop.
The bulbs need to be vastly different from each other to simulate a real home situation. A perfectly balanced load wouldn't mind losing its neutral.
You are correct. It would be interesting to throw a mix of wattages together. I used the same wattages mostly to prove that a balanced load would work.
@@takingmeasure Building a potentiometer voltage divider really demonstrates the value in tying the center back to source. When left in series only it becomes too sensitive to resistance changes. A similar DC circuit consequence as to losing a neutral. Just thinking here. Kind of you to share knowledge in an easy to follow format.
Turn one bulb OFF. No longer balanced.
@@tedlahm5740 Or....on comes a refrigerator which will unbalance one or the other lines.
@@tedlahm5740 True!
It happened to us and we never noticed! I just happened to look up and see that the neutral had been rubbing on another wire and had worn through.
That's not good! Thank you for watching!
The US has so much code, does it really allow two independent circuits to share the neutral?
The short answer is "yes." They are technically a "grounded" conductor and not always a neutral. In branch circuits where a common grounded conductor is shared between two or three ungrounded conductors, all circuits shall be connected to a single breaker so all circuits are disconnected during maintenance or overcurrent events.
@@takingmeasure This is crazy and dangerous and something I would never do. If the ground has an error, accidentally breaks you can easily apply twice the 110V to some device, which you should never do if it is rated for 110V and not 220V.
I would never use a common ground in this way behind the fuses.
@@AlJay0032 Most electricians I know feel the same as you and will not share a neutral (grounded conductor) with two circuits. I am also one of those. Unfortunately, sometimes the neutral is lost at the feeder level, creating an imbalance on many circuits downstream. Thank you for the comment, and thank you for watching.
@@takingmeasureIt's impossible to avoid sharing the neutral at the fuse box, as there's only one neutral between fuse box and outside transformer . But sharing the neutral after the breakers is a problem as it will remain hot when turning off each circuit . It also prevents upgrading to RCBO breakers that have built in GFCI .
@@johndododoe1411 You are correct. I try not to share the neutral on branch circuits. But at the feeder level we have no choice.
So, bottom line, "avoid shared neutrals"! Is that the lesson?!? It's a good lesson, I'm just checking to see if I missed something else. lol
I think avoiding sharing a neutral is a GREAT take-away. Well done! At the same time, this also occurs at the feeder level. I have seen on several occasions where the neutral was lost at the service or even upstream from that! Hopefully, you never encounter that. Thank you for watching and thanks for the comment!
@@takingmeasureOne form, now rarer than before, is for the outdoor neutral falling off the light poles .
@@johndododoe1411 Good thing that is is rare.
Where does one encounter a system such as this? Domestic properties are supplied with one line and one neutral... not two lines and one neutral. Or am I missing something?
That is also my question. And in this demo video all loads act "ohms", because he used incandescent lamps. In reality (50 Hz/60 Hz 230 V/110 V systems) that can differ/will differ.
These systems are common throughout North America. Our receptacles and lights operate at 120V. 22Ov operates larger appliances and motors.
I'm not sure about American systems, but in Europe we typically have 3 phases on every property, even when there are only 1-phase receptacles. They are divided less or more equally between phases. Apartment buildings often have each apartment fed by one of the phases, ie. third of the apartments fed by each phase. When the neutral fails, the voltages between the phases get imbalanced in respect to load differences between those apartments that are on different phases.
@@TheSimoc Rather the same issue but on a larger scale. Always difficult to troubleshoot. Thanks for the visit and comment!
Many (most? all?) homes in North America do this. Most of our electronics are 120V. Some require 240V, e.g. electric clothes dryers, ovens. So we have a neutral and two 120V legs. Leg to neutral = +120V, other leg to neutral = -120V, and Leg to Leg is 240V. So if you lose the connection from the neutral to the transformer outside, current flows through a circuit's neutral wire back to the panel, can't go out to the transformer, so it goes up another circuit's neutral wire and out the circuit's other leg, so now you have two circuits intended to each be 120V both running at 240V. Ouch.
I lost the neurtral. Distroed everything in house, some burst into fire!
I am sorry to hear that. The destruction can be devastating. Thank you for watching and commenting.
If some of your lights are BRIGHT and some are DIM you should immediately kill all power, if you don’t and you use say your toaster your smaller loads like a computer will have high voltage and burn up.
Yes, I agree with you on that!
Congratulations on spelling the word "losing" correctly. That is a rare thing on the internet these days. Most people mess it up and spell it "loosing".
One small victory at a time.
yet another reason to baffle me why America persists in the two 110V split system.. there seem to be many hidden complications/ downsides and very few redeeming features
There are downsides to it, that's for certain.
You lost me when you said 220, there is no such thing as 220V in the US. its 240V!!
I also heard myself say that at one point during the video. Good catch.
Mistake. Switch on neutral is big no, no and disqualify all your instruction.
You are correct. The National Electrical Code allows for switching the neutral (grounded conductor) only in rare and very specialized cases. Thanks for watching!
@@mitchellhegman2402 It was tremendously common, and you'll still find it in many old houses. But don't do it any more.
Great video. I was wondering if you could create another video showing the effect in a 3-phase circuit. Our mfg company is having power drops lately due to power outages, and we are having lots of fried equipment. In one case they said the 480V jumped to 577V, but they don't understand why. I suspect it's a similar situation where we're not losing all phases at the same time. In other cases we've had that happen where a squirrel caused the fusible link to blow by shorting out terminals on the transformer.
@@younda Thanks for watching. A 3-phase lab would be really interesting. I will need to think on that one!
No idiot does house wiring in this manner Period
Wiring methods have improved over the years. Fortunately.
How did you calculate the series values..
@@allantremmel1527 I measured the current and voltage values and then used those to determine the resistance (which varies in accordance with the current/heat produced).
Although this demonstration shows a greatly simplified circuit system, and does not show the grounding system, it pretty well represents the way houses are wired in the U.S. these days.
@@peteduncan921 You are correct. I wanted to keep this pretty simple and to the point. Grounding is a study all to its own. Thank you for watching and commenting.