Odd voltage on 14-3 conductors mystery

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As others have said, I strongly suspect capacitive coupling...with a couple of red flags.

'Phantom voltage' is seen where AC flows through the parasitic capacitance formed between two wires lay beside each other. There insulation is in fine shape and the wires are perfectly usable. When you measure with a 'high impedance' meter (a volt meter that draws very little current) then you see a significant voltage; but when you measure with any sort of load the voltage vanishes.

Phantom voltage is very real, and some of the industrial electricians here, working at 277V with long runs will tell you that you can get a shock from a disconnected wire simply sitting in a conduit with live wires.

What gives me pause simply dismissing this as phantom voltage is the magnitude of the effect you are seeing. Running a phone charger requires more than the microamps that I would expect from capacitive coupling in romex at 120V.

I wonder if you are mixing up two different 'measurements':
A) phantom voltage measured in the wires when disconnected, which is giving you your meter values.
B) current leaking through the switch, measured by the loads getting partial power. Are these by any chance 'lighted' switches?

-Jon
 
winnie said:
As others have said, I strongly suspect capacitive coupling...with a couple of red flags.

'Phantom voltage' is seen where AC flows through the parasitic capacitance formed between two wires lay beside each other. There insulation is in fine shape and the wires are perfectly usable. When you measure with a 'high impedance' meter (a volt meter that draws very little current) then you see a significant voltage; but when you measure with any sort of load the voltage vanishes.

Phantom voltage is very real, and some of the industrial electricians here, working at 277V with long runs will tell you that you can get a shock from a disconnected wire simply sitting in a conduit with live wires.

What gives me pause simply dismissing this as phantom voltage is the magnitude of the effect you are seeing. Running a phone charger requires more than the microamps that I would expect from capacitive coupling in romex at 120V.

I wonder if you are mixing up two different 'measurements':
A) phantom voltage measured in the wires when disconnected, which is giving you your meter values.
B) current leaking through the switch, measured by the loads getting partial power. Are these by any chance 'lighted' switches?

-Jon
Click to expand...

Or dimmers/controllers that use the EG?
 
" only the ground stayed connected" - if there was a high impedance connection to or at the service neutral, via a corroded, loose, or partially broken lug or wire, it could raise the potential of the grounding system well above zero as the current is finding other paths to the source more appealing.
 
I'm going to put a diagram on here when I get a chance. Some of the suggestions I have tried, some items mentioned do not apply. I think I need to clarify the problem more and what is going. I found out I can put pictures up, hopefully today or tomorrow. Please stay tuned. I appreciate you all helping.
 
In addition there are no devices involved. I also checked outlets and switches with a meter for leaks just to be sure. I have so far checked all the oddball stuff that can happen.
Has anyone checked their switched outlets for voltage when the switch is off?
 
You presumably disconnected both ends of the cable in question. But the cable is concealed and you don't necessarily know what it may be running next to that may be (capacitively) coupling to it?

Again as has been mentioned, a low impedance meter or connecting a load to the conductors tested will "short out" a weak capacitive voltage source. If that doesn't make it go away something more then typical phantom voltage is going on here.
 
Dantheelectricman said:
For Lil Bill, my circuit finder when plugged in dimmly lights the LED on it when the switch is off when everything is together as normal.
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Following on my suggestion for using THHN, or equivalent, to extend to the local dwelling load center, instead of a single conductor, just use a long enough extension cord, and plug the light into the end of it, so you can watch what it does with individual circuit manipulations. Start with your circuit finder glowing and turn one circuit off at a time. You can make meter readings from the cord to the load center.

If your circuit finder LED doesn't fluctuate (higher impedance), you should get the Christmas lights (lower impedance, I suspect) from the original trouble observation. What are the electrical specifications for those lights? You haven't shared that yet. I'll bet its a lot different than the circuit finder LED. Personally, I'd start with the Christmas lights, glowing dimly in the extension cord, back at the load center.

Dantheelectricman said:
In addition there are no devices involved. I also checked outlets and switches with a meter for leaks just to be sure. I have so far checked all the oddball stuff that can happen.
Has anyone checked their switched outlets for voltage when the switch is off?
Click to expand...
If I use a d'Arsonval movement meter with an FET (field effect transistor - i.e. high impedance) input, I will measure voltage, voltage that experience has taught me is "phantom."

What you are describing is obviously something that is happening.

The Christmas lights were lit with the branch circuit conductors connected and the controlling switch off. . . enough power got to the receptacle outlet switched hot and neutral to dimly light the Christmas lights. This clearly says there is something wrong. . .

However, everyone here, except you, hasn't (can't) seen the situation. We need your help, for the information you have, to popcorn ideas.
 
kwired said:
You presumably disconnected both ends of the cable in question. But the cable is concealed and you don't necessarily know what it may be running next to that may be (capacitively) coupling to it?

Again as has been mentioned, a low impedance meter or connecting a load to the conductors tested will "short out" a weak capacitive voltage source. If that doesn't make it go away something more then typical phantom voltage is going on here.
Click to expand...


You presumably disconnected both ends of the cable in question. But the cable is concealed and you don't necessarily know what it may be running next to that
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Agree.

From everything the OP has posted it sounds like an induced voltage.
There could be a branch circuit that is running parallel next to, against, the 3 wire , (I assume), NM cable. The thing is the branch circuit would have to have a load connected to it. The current carrying conductors magnetic field will induce a voltage onto the unconnected conductors of the other branch circuit. (Works the same as a transformer). The greater the load current, the greater the magnetic field, the greater the induced voltage.
Assuming the branch circuit wiring is NM cabling.

Just a guess the induced voltage on the de-energize switched conductor for the wall receptacle has always been there. Is the apartment dweller new to the apartment? Was this the first time the type of Christmas lights, that were plugged into the wall outlet, were used on the switched outlet?

What was/is the connected load of the unswitched conductor as it runs parallel inside the same cable along with the switched conductor?

As for RF from a cell tower the OP could rule that out by killing the main breaker at the electrical panel killing all power to the apartment and then measure for the induced voltage.
 
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Jamesco said:
Agree.

From everything the OP has posted it sounds like an induced voltage.
There could be a branch circuit that is running parallel next to, against, the 3 wire , (I assume), NM cable. The thing is the branch circuit would have to have a load connected to it. The current carrying conductors magnetic field will induce a voltage onto the unconnected conductors of the other branch circuit. (Works the same as a transformer). The greater the load current, the greater the magnetic field, the greater the induced voltage.
Assuming the branch circuit wiring is NM cabling.

Just a guess the induced voltage on the de-energize switched conductor for the wall receptacle has always been there. Is the apartment dweller new to the apartment? Was this the first time the type of Christmas lights, that were plugged into the wall outlet, were used on the switched outlet?

What was/is the connected load of the unswitched conductor as it runs parallel inside the same cable along with the switched conductor?

As for RF from a cell tower the OP could rule that out by killing the main breaker at the electrical panel killing all power to the apartment and then measure for the induced voltage.
Click to expand...
Isn't what you described capacitive coupling more so than induction in most cases?

Either way it can have a voltage imposed on it by nearby live conductors.
 
180328-2044 EDT

Jamesco:

A voltage magnetically induced in a wire by a changing magnetic field does not induce a voltage on that wire from a point on the wire to earth or some other reference not on the wire that is not electrically connected to that wire. But, you will see an induced voltage between two different points on said wire.

The voltages on the wire to some external reference are from resistive or other conductive or capacitive paths.

.
 
180330-1159 EDT

Dantheelectricman:

I have not gone back and reread anything, but most, if not all, of your measurements are capacitive coupling.

Since you never break the EGC conductor and assuming it is a low impedance connection to neutral at the main panel, then this is what should be your single base reference for voltage measurement. If you don't trust it, then run your own test lead from the main panel.

A ballpark capacitance between two conductors in a power cable, such as Romex, is 20 pfd. 20 pfd at 60 Hz has about 130 megohms of capacitive reactance. 5 ft is about 26 megohms.

I don't have time to go into more detail at the present time.

.
 
Dantheelectricman said:
Here is a diagram to help clarify the situation.
Click to expand...

So, the neutral never makes it to the outlet on the right?

Is there a switch in the switch box?

Is there a receptacle in the outlet boxes?

What kind of switch is in the middle box?

Are you using the EGC as a return path for the circuit?

Sorry, but I found the diagram to be a bit confusing.
 
180330-1228 EDT

A critical few words I left out in post #33.

"20 pfd" should read "20 pfd per foot" when talking about Romex or similar cable.

With plastic insulated wires in close proximity it is difficult to get down to 10 pfd/ft, and on the higher side could possibly go toward 100. Geometry and dielectric constant are the primary controlling factors.

.
 
To K8 the notes say there are no devices involved, connections are wire nutted, and measurements are taken to ground or neutral. And X means no connection. I thought the diagram was pretty basic and very understandable. Anyone else confused?
I will be going back to the apartment. All the talk about capacitance coupling and such is fine but doesn't explain the amount I am getting in voltage measurements. If this is "normal" then why have I never experienced this amount before. I bet you a million that if anyone else checks their own switched outlets at home you will not get these amounts. Please try it.
 
Dantheelectricman said:
To K8 the notes say there are no devices involved, connections are wire nutted, and measurements are taken to ground or neutral. And X means no connection. I thought the diagram was pretty basic and very understandable. Anyone else confused?
I will be going back to the apartment. All the talk about capacitance coupling and such is fine but doesn't explain the amount I am getting in voltage measurements. If this is "normal" then why have I never experienced this amount before. I bet you a million that if anyone else checks their own switched outlets at home you will not get these amounts. Please try it.
Click to expand...

Actually, I have seen this many times on switched circuits. The voltage is can be as high as 70 volts on a high impedance meter like you are using. That is why I don't use them much for troubleshooting. I use an Ideal Vol-Con and it's indispensable.

I guess I am not used to the way you draw your diagrams. If I am the only one that is lost on it, no problem. That's kind of why I asked the list of questions I did.
 
This will show the presence of 'phantom' voltage along with 'real' voltage by the indication of the neon bulb. It also shows DC and polarity, along with continuity, and there are no buttons to push. I have a couple of these and they are worth every penny.

shopping
 
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