Ghost Voltages - Interesting and Confounding!
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- Опубликовано: 4 июн 2024
- Mitch provides an overview of ghost or phantom voltages and how they can impact electrical testing and troubleshooting. He demonstrates ghost voltage using a non-touch tester, solenoid tester, and digital multimeter.
Mitch uses a Fluke 117 and Klein mm1000 to demonstrate the features and limitations of using the tone setting on a multimeter.
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I’m not an electrician, but I do some electrical work at home but I wanted to thank you for this video because it was very helpful. I’ll be keeping an eye out for your videos. Thanks.
Thank you for the comment. I have not posted for a while, but we are looking at resuming soon.
Nicely explained Mitch, my understanding of electrical circuits has been broadened, this ghost voltage phenomena is clearly capacitive coupling at work, you saved a whole bunch of time, and guess work, thank you.
Happy to have helped, if I did.
Learn something new everyday. I spent an hour+ chasing ghost voltage in some 14/3. Almost ended up cutting into drywall to run new wire; thought maybe I shorted a connector with a staple or something.
I and many others I know have chased ghosts also. You are not alone!
Same thing happened here I had a feeling this was the issue but I didn’t even know that this was a such a wildly known issue
@@KennyTheKenny Ghost voltages can be quite confounding... especially if they are not recognized for what they are.
You can get these phantom voltages in spades from cheapie SMPS modules. I have measured up to 1/2 line voltage on some. Sure, they only produce a few uA and while this is not enough to hurt anyone, it can destroy a MOSFET if it's applied to the gate. So, there are times when you need to take heed of these voltages and do something to mitigate them before you toast some sensitive equipment.
Thank you for the comment. Because I was dealing with power distribution equipment, ghost voltages were more a nuisance than anything, but at your level of circuity I can see how problematic this can be. Again, thank you for sharing this.
@@takingmeasure Understood.
Thank you! I need to buy a Loz meter it seems. I spent 8 hours chasing a phantom voltage the other day! It was 120v, I did IR, and it was fine, so touched it and had no shock, this is when I started looking at this ghost voltage phenomenon. Will I ever need to use the standard volts function again?
Thank you for watching. For troubleshooting basic branch circuits, common lighting circuits, etc., a low-Z meter is great (helpful). But if you are working with circuits that may be impacted due to "meter loading," you would want to use a high impedance instrument. As example, I recently talked with the operator of a powerplant, who told me about technician who knocked the generator off-line by attempting to measure voltage on a relay control circuit with a low-Z meter. In this case, a high impedance instrument should have been used.
It would be interesting to see the reading of an isolation transformer, normally in isolated ground circuits panel if we measure between L1 or L2 and the ground shows 60V when it should be 0V in theory because it is precisely isolated to avoid electric shocks in the patient of hospital.
Thanks for the comment. That is an interesting thought.
I had an issue some months ago with a new ceiling fan installation that had a remote control. The receivers kept burning out. When finally installing a standard fan without a remote a family member said that I had approximately 80v of ghost voltage and it was burning this solid-state receiver out. How do I get rid of ghost voltage?
A ghost voltage is really an "illusion" of voltage produced by the meter. The voltage is not actually present in the circuit being tested. To eliminate a ghost voltage you can simply take measure with a low impedance meter. I suspect something other than a ghost voltage is responsible for damage to your remote. Hopefully you can find the cause soon.
Good eve sir I have now encountered a problem with the LoZ when i test our outlet from the breaker it reads .1 ,and the crt of the lightings also .1 when we insert the circuit of the outlet inside the pipe of the ckt of the lightings,
I am not certain I am following you entirely. But the first thing I would do is test voltage on a known energized circuit to confirm the meter is working properly. Also make certain you are wearing proper personal protective equipment when doing so.
I didn't like one of the solutions proposed, de-energise adjacent circuits.. If there is an unintended short to one of them you will not then catch it.
Regarding the voltage seen , lets say a good quality DVM has an input impedance of 10 M ohms, also lets guess at 100pF stray coupling capacitance. This would be ~25 Mohms at 60 Hz, so on a 110v circuit you would measure about 30v . If we had a 10 k ohm load we were measuring across we would see ~30mV (factor of 1000 Mohm to Kohm). If we looked across a live circuit we would dissipate 1.2 watts. You can buy DVMs with a low input impedance for precisely this job. this quick sum show its not an intractable problem
Your point is valid. There may also be a lot of instances where it would be impractical or undesirable to de-energize adjacent conductors. Life-safety circuits, for example. Thank you for the comment.
The measured Ghost voltage measured 79VAC Phantom/ghost voltage from the white neutral wire of the power supply to the N/C white neutral wire of the cord and the same from the green earth wire of the power supply to the N/C green earth wire of the cord measured 79VAC phantom/ghost voltage. The question is why 79VAC is the phantom ghost voltage and not 120VAC? 120VAC real -79VAC ghost= 41VAC difference or loss.
That 79V is caused by induction and it's value depends on many factors like wire length and etc.
@@ghenkhoash2440 79VAC is an induction by coupling but why 79VAC and not 120VAC?
That's a physical phenomenon! I told you the 79V depends on many factors. The 2 wires are not touching. A good electrical engineer could probably calculate that voltage using Maxwell equations.@@waynegram8907
The value of the ghost voltage is related to the length of the wire capacitively coupled with the energized ungrounded wire. We might see a voltage nearer to 120V if the "floating" wire was longer and provided more capacitance when coupled. A mush shorter wire would yield less voltage. It might be fun to do a lab on this...
Yep!
@@ghenkhoash2440