Odd voltage on 14-3 conductors mystery

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Dantheelectricman

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Sun Prairie, WI
I have a large apt complex that has strange voltage appearing on unconnected wires in the same cable. It first came to light when the tenants noticed the Christmas tree lights were on dim when the switched receptacles were turned off and the phone barely charged.. I have separated all conductors from the switch to receptacle and receptacle to receptacle. When it was all connected I got about 65 volts on the switched off half of the outlet.. When separated as above I got 45 and 25 volts depending on wire length. With all wires separated I could hook 120v power to any of the 3 wires and pick up the lower voltage on the other two to ground or neutral. The 3 way hall switch wire did the same thing. Lower voltage on the travelers. Checked with different meters I got no reading between any wires. Somehow a voltage is being induced on the others with no physical connection. I am going to check the model apt also. Maybe its building wide. Checked with my distributor for any wire recalls. Built 2002. Anyone heard of this before? I pride myself on being a good trouble shooter but I am stumped so far.. New here and hope someone can steer me right. Thanks.
 
It's not uncommon to see a phantom voltage between wires in a single cable or conduit. Are you using a high- or low-impedance meter? If all you have is a high-, try connecting a 25w light bulb between the mystery conductor and a neutral and see what voltage you read, chances are it'll be close to zero.
 
zbang said:
It's not uncommon to see a phantom voltage between wires in a single cable or conduit. Are you using a high- or low-impedance meter? If all you have is a high-, try connecting a 25w light bulb between the mystery conductor and a neutral and see what voltage you read, chances are it'll be close to zero.
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Two clues here that strongly point to capacitive coupling, causing phantom voltage, are
1. that the effects to a load are seen only with relatively high impedance and sensitive devices like small LED lights and electronic power supplies like phone chargers. (If you originally had a 25 watt string of incandescent bulbs or a power supply that needed a higher minimum voltage to produce any output the phantom voltage might never have been noticed.) And,
2. That the effect is symmetric on the 3-way traveler run regardless of which of the two travelers is powered.

By measuring the voltage across a known resistive load (like a 25W incandescent as long as you measure the cold resistance instead of calculating from wattage and voltage) you can determine the current which the phantom voltage can source. It should be well below the 6ma threshold of a GFCI. If it is not, you might still have a problem which requires further troubleshooting. Another way to determine the current is to put your multimeter, in amps/milliamps mode, in series with the 25W bulb.

How long are the cable runs in question? If on the order of 100' or more, phantom voltage is to be expected.
 
With a capacitor meter I read about .5 picofarads. All meters I tried gave no different voltage. One run is about 5 feet, 20 feet, and 30 feet. Why don't I get this at home then or when checking 3 way switches for correct wiring? I have never seen these readings when checking for incorrect wiring. These voltages are present with no load and all ends free except the one I connect to 120v. I can see maybe a few volts but 65 volts.
 
Dantheelectricman said:
Checked with different meters I got no reading between any wires. Somehow a voltage is being induced on the others with no physical connection.
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Welcome to the Forum, Dan.

Intriguing problem.

Help me understand what you are measuring "to" when you are finding voltage. I assume you are using some form of a two-lead voltmeter, one lead on the conductor you describe, and the other lead is on . . ??

Also, what is the wiring method? MC, conduit, NM-B?
 
Dantheelectricman said:
All meters I tried gave no different voltage.
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Do all of your meters have digital displays, or are some a "moving needle" (d'Arsonval moving coil)? Digital display voltmeters almost always have high input impedance, while the d'Arsonval meters have low impedance generally.
 
14/3 makes me immediately suspect a malfunctioning multiwire branch circuit. I would check all affected circuit voltages in the panel. I am not seeing how capacitive coupling would appear now 15 years after the place was built.

you could try swapping out the breaker of the affected circuit with a GFCI or afci breaker and see if that will pick up any faults.

Eta: nevermind, disregard all of that, I missed the word unconnected in the original post.
 
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Meters are fluke 70 III, greenlee amp probe cm-750, and a mastech 390-545.
All read the same. Even a 5 foot piece has "stray voltage". Measures were taken from the affected wire to ground and neutral. Power could be connected to the white, black, or red of the nm-b cable individually and show a reduced voltage on both other conductors. Remember all ends are free of connection except one connected to 120 volts. Only the ground stayed connected through the cables. I turned off power to every room but that circuit and turned off power to that circuit with all others on. No interconnection at all. Just checked my switched outlets again at home with LED string lighting plugged in and lamps but I got 0 volts with a room full of outlets with the same meters when switched off. There is only 2 switched outlets in the apartment living room.
Volts read are 65 when all connected normally at the outlet when read at the switched off half. When split up ( all wires disconnected from each other and tested separately) the 5 foot run reads 25 volts and the 30 foot run is 45 volts. Five volt difference from read as a whole. Hope some of this helps. Thanks again.
 
Dantheelectricman said:
Meters are fluke 70 III, greenlee amp probe cm-750, and a mastech 390-545.
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Well, the Fluke and Greenlee are both high-impedance meters (didn't check the mastech), so that's not surprising. Try the lightbulb trick. Lots of us use low-impedance meters like the Fluke T+Pro or a "Wiggy"-type tester for troubleshooting.

Basically, phantom voltages happen, and usually they're nothing to worry about. You can search these forums for more discussion about them. (If there was a phantom on a receptacle circuit, why wasn't it energized from a breaker?)

BTW, do you have a Megger(tm)? If so, have you done an test with it? It might show a higher-than-expected leakage between conductors.
 
Dantheelectricman said:
Meters are fluke 70 III, greenlee amp probe cm-750, and a mastech 390-545.
All read the same. Even a 5 foot piece has "stray voltage". Measures were taken from the affected wire to ground and neutral. Power could be connected to the white, black, or red of the nm-b cable individually and show a reduced voltage on both other conductors. Remember all ends are free of connection except one connected to 120 volts. Only the ground stayed connected through the cables. I turned off power to every room but that circuit and turned off power to that circuit with all others on. No interconnection at all. Just checked my switched outlets again at home with LED string lighting plugged in and lamps but I got 0 volts with a room full of outlets with the same meters when switched off. There is only 2 switched outlets in the apartment living room.
Volts read are 65 when all connected normally at the outlet when read at the switched off half. When split up ( all wires disconnected from each other and tested separately) the 5 foot run reads 25 volts and the 30 foot run is 45 volts. Five volt difference from read as a whole. Hope some of this helps. Thanks again.
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I have to agree with Zbang, that you are being mislead by phantom voltages.

The Mastech 290-545 is an older vanilla DMM (LCD display, high input impedance). All three of your meters will, basically, read static electricity without dissipating it.

Your descriptions have hints that you are dealing with a failing neutral connection in a multiwire branch circuit (Article 100 "Branch Circuit, Multiwire"). To rule this out, verify that the homerun to the circuit breakers does not share a neutral with another circuit breaker's conductor.

I believe that what you are describing, the wires that you are measuring voltage on when they are disconnected (at both ends), are those of a single circuit ( 1 hot, 1 neutral ), but the branch circuit could combine with another in a multiwire homerun. Any place the multiwire neutral is spliced could be the seat of the symptoms you are tracking.
 
This is why I do all testing with my solenoid tester (K-60) unless I need actual voltage numbers, but then the load is usually connected. To me, high-impedance meter readings are basically meaningless.

I suggest measuring all these wires again with an incandescent bulb in parallel with the meter leads, even one as small as a night-light bulb, which would double as a visual "real electricity" indicator.
 
This is not a multiwire circuit. The 3 wire cable is from switch to outlet, outlet to outlet, and switch to switch. Homerun is a 2 wire. Still get it even with every other breaker off. If it's my meters why do I not get it at home or anywhere else I have checked 3 wire cables in my 43 years? I've been using the same meters for 15 to years. I know a few volts is normal. Not 45 to 65 volts on a 5 foot length of wire. I know off voltage can be read when the battery gets low even though the battery indicator doesn't show.
 
Would some of you check your own switched receptacles and tell me what you read at the receptacle When the switch is off. I get absolute 0 using the same meters. The apartment reads 65volts with everything unplugged.
 
Thank you for ruling out multiwire.

I had a case where nearby radio transmission towers would cause time-of-day erratic behavior in a key service phone system until the many unused cable conductors were intentionally grounded and bonded to the Grounding Electrode System.

Is there a cell tower nearby? TV, FM ?
 
A cell tower is a good 1/4mile away but I have one even closer and it doesn't affect me and the reading I take here. I know what you mean by a strong signal affect. I dabble in electronics also ever since I could hold a soldering iron. Can a video be posted here to maybe better explain it. Maybe I can draw a picture diagram to help. I see a bunch of icons above. Computers and the like are not good friends with me. Give me a wrench or screwdriver and I am fine. I thank everyone so far with suggestions. It all works to a solution eventually I hope.
 
Get a night light or a lamp with the lowest wattage bulb you can get. Plug it into the switched half of the receptacle with the switch off. If it lights/glows, go and turn off every breaker except the one the switched receptacle is on. Do this one at a time while watching (or having someone watch) the bulb. If it goes out when a certain breaker is turned off then you know you may have an unknown/unwanted connection with another circuit that is backfeeding to your receptacle.
 
Its been a bit difficult to follow.
Have you checked to see if you a a neutral problem at the service, or one of the other apartments?
 
Sierrasparky said:
Have you checked to see if you a a neutral problem at the service, or one of the other apartments?
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LarryFine said:
That's what just popped into my mind, too: energized "ground".
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That opening observation suggests there is some amount of energy, more than static, getting into this bit of wiring:

Dantheelectricman said:
I have a large apt complex that has strange voltage appearing on unconnected wires in the same cable. It first came to light when the tenants noticed the Christmas tree lights were on dim when the switched receptacles were turned off and the phone barely charged..
Click to expand...
 
Following on Little Bill's suggestion about the night light, having gotten it to glow at the switched receptacle, then use a piece of THHN, or other insulated conductor, to run back from the switched outlet (s) to the local circuit breaker panel, and do measurements there using that same light.
 
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