What is Ghost Voltage?
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- Опубликовано: 11 июн 2022
- Bryan teaches the techs about ghost voltage. He explains what it is and why it happens.
“Ghost” voltage refers to a voltage that we can detect but that doesn’t appear to be doing anything. It could also exist but go away once the circuit is energized. It can be useful to think about there being static pressure against water pipes and then having it go away when a faucet starts running.
The meter itself is a load, as it creates an electrical path. A meter has very high resistance, and you’ll see voltages across the meter due to that high resistance of the meter. When there is an actual current and a lower-resistance load in the circuit, the “ghost” voltage disappears.
When you energize the primary on the transformer and have an open circuit on the secondary, that transformer does not appear to draw any current even though we have 240v of electrical potential. Instead, there’s an excitation current, which is a very small current due to inductive reactance and back EMF.
We often imagine that electricity consists of electrons moving in one direction, but electrons are really a bunch of tiny energy units that move erratically. The sine wave generates the motion of electrons, and the sine wave represents an electromagnetic field that generates the circular motion of a motor. So, adjacent wires can be affected by the electromagnetic field if they’re within range; they pick up tiny amounts of voltage in a phenomenon called “induction,” which is what happens when power from the primary goes to the secondary without actually touching the secondary. The same principle applies to the interaction between two sides of a capacitor.
So, whenever possible, we want to keep conductors as far apart as possible. We can also use meters that have a low-Z setting, which uses a lower resistance than a typical meter and doesn’t pick up those “ghost” voltage readings.
We can also see ghost voltage when you measure across a load (like a contactor coil) when you have an open thermostat switch. You may end up with 24v across the load, but that could drop to 0v when the switch closes. That’s because there could be additional resistance in the circuit, and the voltage drop exists because the movement of electrons is dynamic rather than static. When that happens, you can look for poor connections or other causes of high resistance.
Veritasium video: • The Big Misconception ...
Check out the article on ghost voltage at hvacrschool.com/beware-ghost-...
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
Great info. Thanks Bryan
I'm close to being 61 years of age, I have been a HVAC/ Refrigeration technician for a little over 42 years . I have had my share of fun with both high and low ghost voltages
I enjoy watching your videos and still able to get great information from them
Just wanted to thank you for sharing your knowledge
Man Brian your employees should be happy to have a boss like you to keep them schooled on all subjects that if not now one day they will appreciate ya! Stay blessed!
Had a ghost voltage problem recently on the ignition circuit of a forklift, the fuel shutoff solenoid would not stay on reliably. Finely checked the ignition switch, which was cooked. Totally different field, but same problem. Good explanation Brian.
Very impressed with your knowledge and experience but especially your patience
Love the content, been watching for years now.
One of the best HVAC channels on RUclips
The first time I ever realized I was dealing with ghost voltage was a gas furnace and the gas valve wouldn’t open even tho measured 26v at the valve it would drop out. Stick a contactor on it and it won’t pull in.
Ends up being the contacts on the control board for the gas valve have high resistance.
Appreciated sharing it. Never dealt with loss at CB before. Learned something...
Contactor trick is definitely on my magic tricks now on. Makes a lot of sense
I have seen high resistance cause some weird reading before too but ya checking under load is the way to go
Voltage only measured on October 31st? Good video.
Very well explained. Thank you!
Great job Bryan!
I feel v happy while watching you and your teaching
I've noticed you said high resistance but I have noticed a low resistance taking place with the same problem. Such as the reversing valve measuring 2 ohms and causing ghost voltage and damaging the transformer and not blowing the fuse. Thanks again for the great content. Very informative.
Not blowing the fuse at 2 ohms resistance? I would definitely check that fuse size. Someone had to substitute a 15 amp fuse in place of the 5 amp to keep it from blowing and it resulted in the transformer blowing.
This is a case not of ghost voltage, but of ghost hackery.
Oh boy... I will never forget all of my past 3 ghost voltage calls ⚡⚡⚡⚡⚡. Hardest one to find - bad splice to transformer.
💪💪💪 Make me feel like I'm a ghostbuster
6:23 the term "sine wave" comes from the root sinusoidal, which simply means circular or cyclical, and is in reference to the graph of a cyclical wave form. What's creating the wave of motion - or drift - in the electrons is the electromagnetic field that is set up in the wire via the source (battery, rotating magnetic field, etc). This field is called the Poynting Vector for those who wish to grease the Google machine.
@JCPOOLE MECHANICAL I applied, but was rejected because I dont have gas license (Canada). Working on gas license at the moment. I'm half decent with physics and know a bit of electrical. I build and trouble shoot PCs as well.
The only question I have is why would an additional place of resistance in the circuit after the load, I'm talking about the wirenut here, cause ghost voltage or cause the voltage being supplied to the intended load to not be able to have enough voltage to do the work? Or to get a reading at least across the intended load? Cuz I could understand if it didn't do work because it's not really completing the circuit with enough voltage but wouldn't I spell read 24 volts across the contactor coil in this illustration? And then lose voltage after the wire nut?
Good stuff, but you forgot the capacitive coupling as another source of ghost voltage, not only the inductive coupling exists ;-)
This reminds me of lockout relays that have high impedance coils. Current will always want to flow to the path of least resistance. The high impedance coil becomes part of the neutral.
Also this important to remember because, nowadays most equipment is communicating hardware, where electrical noise as I call it, will create havoc on hardware and nuisance call backs. Vfd are well known for this because how they generate an artificial sine wave.
Current takes all paths available proportionate to resistance. Lower resistance paths will see more current, but all available paths will see some current. Kirchhoff's current law.
Micro electro magnetic pulses caused by the constant reversing of polarity. ( Alternating current ) or your sine wave you mentioned .
On your wave drawing, the top curve being the plus or push pulse, the bottom wave curve being the reverse/ negative or pull pulse and the center of these two pulses is a zero volt point or the start point of reversing, or the ending point
The Veritasium stuff was a distraction and too much detail. (Not everyone even agrees with the theory in that video.) Simple leakage voltage/current explains most 'ghost voltages', the quality of the electrical devices and equipment are not extremely high on the systems that most of us encounter in the field and they allow acceptable amounts of leakage. Inductance is absolutely a cause as well but physical voltage leakage is the most common cause. Not your best presentation that I have seen, but I am learning a great deal from you as I move into Refrigeration from Electrical Contracting. You are an excellent instructor.
Oh and the never ending time delay can be very confusing the first time ya run across it. After that one time it’ll never get ya again
"Can you be quite for a second" lmaoo
There's a lot of info about transformers available online. You can literally go as deep into the weeds as you want. Giving that a try will provide a lot of insight into why your transformer is doing what it's doing.
Had that exact issue and bypased tstat, isolated y circuit, 5amp fused popped found shorted coil contactor coil. Replaced c and fuse , now mt tstat and my vs blower motor started working again
What about when the transformer secondary is not anchored to chassis ground and you get these weird readings when you measure to ground? Is that ghost voltage?
Good 👍 👍
The "hum" in a transformer is primarily due to the billions of microscopic poles in the core aligning and realigning to the magnetic field changing 60 times a second from the AC voltage.
I had a residential system with the breaker off to the disconnect I would get 23v on one leg and 18v in the other but 7v between the legs. I never seen ghost voltage this high. Any thoughts?
i would assume a surface charge on the capacitor, but that is simply a guess. i might press in the contactor to see if i can eat the charge.
Did you ever locate the origin of the issue you think?
one change out i kept getting shocked on the line set outside. it felt like 24v. all power was off. i was confused.
so there's volt meters with low impedance ("z") setting, to check the ghostiness of the voltage
Yes a lot of high end meters even my field piece sc640 has like 2/3 settings for voltage.
50v and under 200v and under and 400v and under.
All these have less impedance and can more accurately measure the voltage closest to them.
A 100A clamp on amp meter is very handy for checking down to 1 milliamp.
Is this the same as phantom voltage?
Mitsubushi mini split branch boxes have ridiculous induction in communication cable. Ive seen indoor unita do weird stuff
They specifically tell you to use separate cables for this reason, unlike Daikins that will work with multi core
@@mikebazil1 it is true!
I'm Measuring voltage on a kauri boat I have 8v@ .01a between my battery +tve and mast. Loading doesn't influence voltage. I can remove all electrical systems and get a lower voltage at the same current like 2v .0.09amp. Either way any through bolt is earthing thru draw and creating sodium hydroxide Around any grounding metal . I listened to this and figured I'd I create a load system between the high potential areas thru resistive led to cancel the voltage apply opportunity for the voltage to draw current with hope that at chance it'll cancel the voltage but the resistive quality actually increasing current causing more ionic discharge thus effecting the ionic chaste aping my thru bolts enhancing the alkalinizatation effect. Thus destroying the lignum in my wood. I can't seem to discharge the capacitance of my mast. Advice master E
My guess is. if I create a lower resistive circuit that grounds the boat the saline imbued woods resistive quality will no longer be a primary circuit. All this ghost voltage on my mast. Is capacitance? Yea?
If I was 2 stories high my voltage would increase. I have a nasty that is 30m if not more high with a variety of conductors at the top. Nav lights aerial etc. Then I have a solar panel. Conduit coming through the same port in thinking inductance with the lines running parallel and capacitance within the mast being wooden also? Sound right?
I think I've come across ghost voltage. Was getting 0 volts at the board, but when I removed the wires I was getting 24v
I wasted my time changing a gas valve because of ghost voltage lol
@@mackenziegray2090 😅😅
The "ghost" or "phantom" voltage being discussed here is usually due to CAPACITIVE (not inductive, as being implied) coupling. Just call your local Fluke office and they will be glad to visit you and explain all about ghost voltages (and sell you all kinds of meters that will detect it 😀) Also in the referenced article, "but it also drops the impedance of the contactor coil itself," is very strange indeed. Impedance is a fixed property for a given circuit frequency. What is being described here is a simple "voltage divider" circuit confused with a lot of crazy talk. This gentleman is a wealth of knowledge and wisdom when it comes to air conditioning service, but electrical theory is not his strong suit.
Can you elaborate on the difference? I have always called it inductive when I have numerous conductors laying in a trough for a long distance. 120 on a few of the wires "induces"?? a voltage on the wires next to it similar to a transformer.. Never thought of it as capacitive, but only because I have not thought about it much at all except to not be misled with meter checks.
At least he's trying
"ghost voltage" or "excitation current" printed on a T-shirt would be great merch 👕
I think that a ghost voltage is that electrostatic force that surrounds a ghost gun, does that sound reasonable?
Updoot for Veritasium reference
If you switch to low inpeadeace setting on a meter like the fluke 177 it will show 0.00 which will indicate it’s not a true voltage.
Bert got yelled at lololol
You see a lot of this when dealing with snubber circuits, like some trane circuit boards
So, if I sneak out at night and wrap a wire around the power line next to my house - I can get FREE power! lol
"Who you gonna call..." 👻
Why do good instructors, such as you, ask the students questions? We are here for you to teach us. To go around the room to hear stupid response waste to much valuable class time. Thanks, great videos.
a) to engage the students minds rather than just have them sit there on auto pilot.
b) to get feedback on how you are doing as a teacher. have you confused the class with a previous lesson? did the class get wrong information you need to deal with from somewhere else? how can you explain the subject to your students in such a way to deal with any false assumptions they have? the answer to all of those questions starts with knowing what the students think.
You can get a feeling of what the class knows and does not know, and you can adjust your style or wording. Good instructors will do that
Nest T.stat going crazy doing nothing or sometines saying it can't operate with how it's wired and sometimes working turned out to be a bad condenser 24V contactor.
Was a recent time consuming "fun" learning expierence to figure out.
Never heard of it called ghost voltage before.
I always call and hear such to be called PHANTOM VOLTAGE ⚡️
I would say 50% of the time I have a failed NEST or Y1 problem on nest it is the outdoor contactor. Since they’re so cheap I almost always change the contactor if I go on a call for a problematic nest thermostat. Been at least 5 now.
I had a nest T-stat that was giving and ERROR ON Y-1 code. It does this using DC voltage and could measure the resistance was out of range. I believe.
Anyhow the transformer which had a 3 amp fuse on common and hot 24v kept blowing. Not the fuses but the transformer. Because the voltage/resistance ratio was just so odd it wasn’t blowing the fuse but the actual fucking transformer.
I was pretty new at the time and that call kicked my ass. Now I’m not scared of too much.
Thanks Bryan Orr. Love you
i had an issue like that with a contactor. not funny
I just came across this today, wasn't fun.
Was he talking to the ghost?? Can you be quite???
Asks a question, someone answers and then tells him to shut up