Ghost Voltages - Interesting and Confounding!

[@McmM-cv9sb]

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.

[@takingmeasure]

Thank you for the comment. I have not posted for a while, but we are looking at resuming soon.

[@texassparky]

Thanks. I'm a JM spent most of my apprenticeship doing new commercial construction. That training was invaluable because u have to learn how buildings are built. Newayz. Man, when I moved to service the game changed! U gotta learn and learn quick. I learned this "ghost voltage" 2 yrs ago on a service call to a house. With breaker off I was still getting 30V on a fan/light switch. I intuitively knew it wasnt possible and even showed the homeowner I could lick my finger, ground myself out and touch the hot and nothing would happen. "dont do that handymen". I knew it was inductance but couldn't prove it at the time. Bothered me so I started doing research. In short learned about LowOZ meters and began teaching my apprentice about it. LowOZ is all I pack out now. Always working, always learning! Great video. Thank you.

[@takingmeasure]

Thank you for the comment. Early in my career, I spent a good part of a day chasing a ghost voltage. They can be tricky and someone needs to teach you about them.. I am pleased that you are teaching others about this and anything else that is of helpful. Good stuff!

[@ecospider5]

Wow insulated gloves in a demonstration. Seriously I can’t remember the last video where I saw insulated gloves. Well done!!

[@takingmeasure]

Thanks for watching. We try our best to adhere to the best safety practices.

[@brianjc85]

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.

[@takingmeasure]

I and many others I know have chased ghosts also. You are not alone!

[@KennyTheKenny]

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

[@takingmeasure]

@@KennyTheKenny Ghost voltages can be quite confounding... especially if they are not recognized for what they are.

[@Jfarr1978]

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?

[@takingmeasure]

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.

[@alejandrogalarza3147]

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.

[@takingmeasure]

Thanks for the comment. That is an interesting thought.

[@uni-byte]

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.

[@takingmeasure]

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.

[@uni-byte]

@@takingmeasure Understood.

[@martincraven3835]

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.

[@takingmeasure]

Happy to have helped, if I did.

[@igleseriotigon7744]

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,

[@takingmeasure]

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.

[@stanbest3743]

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

[@takingmeasure]

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.

[@wdmm94]

The old part of my Dad's house was (and still is) wired with an old 240 volt main and range pull out fuse panel with 4 screw in fuses, in 120 volt 15 - 20 amp circuits (small 5 room house when wired in 1949). Those 4 old circuits only have two conductor wiring - no ground wires. I know exactly what fuse turns off what light and what outlet- pretty straightforward and simple. Has a sub two circuit fuse box wired with 10-2 w/ground wire tapping off each 120 leg where the "handyman" used the ground wire as the neutral (installed in late 60's). I only figured this out on close inspection 20 years ago when my computer surge strip indicated no ground on these newer three prong "grounded" outlets in this addition. The "grounds" in these outlets had just been screwed back to the sub fuse box and ended there. So much for assuming the outlets were working three prong outlets. Anyways there is also one three prong outlet with newer type 12-2 with ground wiring on one of the old fused two wire circuits. Now this should have dawned on me sooner, knowing this circuit leaves the fuse box on old two conductor no ground wiring, that this particular outlet can't be grounded. I was working with this outlet and was running voltage checks before taking out the fuse, -hot to neutral, hot to ground, neutral ground. I could not believe it, but I was getting voltage readings on the neutral to ground???!!! (like 60 volts or whatever) and of course the hot to ground (but no where near 120). I was totally baffled as to what was going on. Of course pulling this circuits fuse out killed everything. I wasted several hours trying to get to the bottom of this. I even put one voltmeter probe on the nearby metal sink that is all plumbed with pvc in an all wood counter and could get volt readings. I was trying to figure out a way I could see if there something bad going on. It finally dawned on me that the ground wire couldn't (even though misleadingly attached to this outlet) be hooked up to anything and I was getting some wierd effect when checking voltage on neutral to ground with hot energized - with nothing plugged in or turned on in circuit. I simulated this out in my shop where I had one stand alone outlet hooked up to 20 feet of 12-2 w/ ground wiring in the breaker panel and disconnected this outlet's ground. I turned off all other circuits in box and was getting voltage readings in neutral to ground wires (way less than 120 of course). That was very interesting. This is also why I generally just kill everything whenever working on anything electrical. You just never totally know what has been done or what might be going on.

[@wdmm94]

My question would be is there any way to see if something like this was actually somehow energized - or partially energized for real?

[@takingmeasure]

Many years ago, I had a somewhat similar experience the first time I encountered a ghost voltage. I wasted several hours "troubleshooting." Thank you for sharing your experience here.

[@wdmm94]

I also realize without being able to physically track and see this wiring to never assume either. I don't remember if I decided to disconnect this ground because it probably wasn't doing anything and just to be safe, but I did note on outlet that it was NOT grounded. On another circuit I was fairly certain that the hot wiring went from fuse to light socket then to switch (light socket hot with switch off). I think a guy almost needs to have an independent grounded wire and rod while trying to sleuth down antique houses that have had decades of layering. I had another issue with a light not working in my Dad's boyhood farmhouse. This house had some lighting from a 32 volt DC light plant in the 30's and 40's. My recent understanding of these systems was that they generally used light sockets and outlets same as 120 stuff in anticipation of being wired up AC eventually. Might have been knob and tube. I have a couple of 32 volt farm radios that have the same cords/plugs basically as 120. This house had an old time 4 or 6 circuit breaker (!!!) panel. Still has two prong outlets etc. Twenty odd some years ago a new breaker panel was installed with wiring to energize old circuits in this panel with insides removed. Just tied to old house wiring that came into this box. I pulled down light fixture for this light and pulled out switch cover. This was even worse in that it was old rubber cloth stuff that as I recall didn't match what was in switch or old breaker box. Both wires looked alike basically. I couldn't make head or tales out of anything much less try to troubleshoot. I also hadn't really verified which outlets and lights were with what panel circuit etc. So I didn't have as clear of a picture. I also have no idea what work has been done over the years etc. I didn't waste a lot of time on that, never really got to bottom of this, and light started working again. I think I also put some ox guard on new breaker contacts in case this was the problem - aluminum bus bar in a dampish basement - original breakers were on first floor.

[@wdmm94]

Makes me wonder why electricians don't use ox guard on new install everything as it is all pretty much aluminum now and so prone to oxidation / resistance heating / poor contact arcing issues. I seen this in a 20 year old breaker box in a building at my dad's with a 100 amp main breaker chewing up the contact on the bus bar about 20 years ago. I was told 30 years ago by an electrician to use ox guard on the aluminum stuff I was installing at that time. He also told me to run the underground aluminum cable in a drain tile to protect it. My dad also had a 20 year old buried aluminum cable fail 20 years ago too. It was all under a lawn. Another guy year ago told me how some mobile homes from 70's (??) had aluminum wiring and the terminal ends of this wiring would get hot and burn them down - oxidation.

[@takingmeasure]

@@wdmm94 Using a voltage tester or meter with a low impedance input will tell you for certain. The ghost voltage is partially the function of the high impedance input of the DMM or tester.

[@delectrico-sma]

Gracias por usar guantes. ¡Me suscribo! 🧤 Thank you for wearing gloves. I subscribe! 👍

[@takingmeasure]

We try our best to be safe.

[@devild2269]

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?

[@takingmeasure]

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.

[@waynegram8907]

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.

[@ghenkhoash2440]

That 79V is caused by induction and it's value depends on many factors like wire length and etc.

[@waynegram8907]

@@ghenkhoash2440 79VAC is an induction by coupling but why 79VAC and not 120VAC?

[@ghenkhoash2440]

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

[@takingmeasure]

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...

[@takingmeasure]

Yep! @@ghenkhoash2440