43v in circuit when breaker switched off

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SDmark

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My 1950s San Diego home had a master bedroom added in the 70s, I think it was. There is a 12-3 cable going to the addition. Cable has red, black, and white wires, no ground wire. Circuit #3 is the washer and gas dryer. Circuit #13 is the rest of the bedroom. Breakers for #3 and #13 are both on the left side of the breaker box.

Using a digital voltmeter at a junction box before the cable enters the addition, I see what to me are some strange readings [updated 2/17 including black and red, with 240v circuit on opposite side of panel on]:

Both breakers off:
Black and white: 1v (started about 3.5v and declined)
Red and white: 1v (started about 3.5v and declined)
Black and red: 0v

Only breaker #3 on:
Black and white: 41v
Red and white: 120vv
Black and red: 74v

Only breaker #13 on:
Black and white: 119v
Red and white: 44v
Black and red: 69v

Both breakers on:
Black and white: 119v
Red and white: 121v
Black and red: 241v

Is it normal for there to be 41-44v on a circuit that is turned off? If not, what could cause that and how do I fix it?

Thanks very much,

Mark
 
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Jadnashua

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A high impedance multimeter can give some weird readings, and may not indicate anything unusual. Is there any 240vac device fed from that box? If so, it could bleed some power back across through to the other side under some conditions.
 

SDmark

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Is there any 240vac device fed from that box? If so, it could bleed some power back across through to the other side under some conditions.

In the breaker box, electric oven is on same side #7 and 9. Electric cooktop is on opposite site, #8 and 10. So if I turn those off, no bleed?

I was using a digital multimeter. Would an old analog multimeter be better?
 

hj

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Both breakers on the same side of the box is irrelevant. Unless they are connected to different "phases" of the incoming 240v line, your neutral can be overloaded. You do not give a red to black reading. It should be 240 if the "common neutral" wiring is correct. if it is zero then it is incorrect. We have no way to tell whether you have some device backfeeding into the "dead" circuit when you turn the breaker off.
 

Lone Star Charles

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Try the same measurements with your old analog multimeter and let us know what you get. I suspect that jadnashua is correct.

Cheers
Charles
 

Lone Star Charles

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Try the same measurements with your old analog multimeter and let us know what you get. I suspect that jadnashua is correct.

Cheers
Charles
 

SDmark

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You do not give a red to black reading. It should be 240 if the "common neutral" wiring is correct. if it is zero then it is incorrect.
I've updated the original post with new numbers including red-to-black.

If I turn off EVERY breaker in the (sub)panel except #3, I get these readings:

Only breaker #3 on:
Black and white: 43v
Red and white: 120v
Black and red: 72v

If I go to the outside panel and turn off the subpanel, I get perfect 0v on all--not even the 1v I was getting with the both #3 and #13 off.

We have no way to tell whether you have some device backfeeding into the "dead" circuit when you turn the breaker off.
As best I can tell, this is the first junction box after the circuit breakers. But it's a fairly long feed and it's old non-metallic cable. I have vaulted ceilings and from toning out the feed, it seems to be running inside one of the beams and for a short distance, on top of the roof under the rolled composition roofing material (the roofing granules have actually detached along the cable run). I was worried that somehow the red and black were touching, but then with one breaker on, I'd have 119v and not 43v, right?
 

SDmark

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Here is a pic with closeup of the top of roof above cable run. The granules are completely gone and the material is soft in the closeup area, which seems to be where it comes up to the roof. Sure hope there isn't an unprotected junction under there but I've seen some odd things in this house.

What kind of cable should they have used under the roof like that? Underground Feeder? Can one also use UF inside walls? Just wondering how I'd replace the cable if I had to...

20160217.Cable to master bedroom under roof.jpg
20160217.Cable to master bedroom under roof.closeup.jpg
 

Cacher_Chick

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No electrician would bury a cable under the asphalt roofing. It should be within the rafter framing or in an approved raceway.
 

Reach4

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If I turn off EVERY breaker in the (sub)panel except #3, I get these readings:

Only breaker #3 on:
Black and white: 43v
Red and white: 120v
Black and red: 72v

Try Black and red with both breaker ON. It's important.
 

Jadnashua

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Many DMM's input impedance can be hundreds of MegaOhms, so you could read a voltage, but there would be no current of any consequence. An old analog meter is likely 20K-ohms/volt. If you do not know what you are doing, either one can give an inaccurate, or misleading reading.
 

SDmark

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No electrician would bury a cable under the asphalt roofing. It should be within the rafter framing or in an approved raceway.
Dug up the old permits for the addition from 1970. Good news: there was an electrical permit with rough and final inspections. Bad news: contractor = "Owner".

The roof was replaced in 1991. There's no obvious bump in the asphalt, but that strip of missing granules above where the cable is toning loudly makes me wonder. Will be interesting to see what is underneath the asphalt next time it is replaced.
Try Black and red with both breaker ON. It's important.
I added that info to the very first post:

Both breakers on:
Black and red: 241v
 
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WorthFlorida

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In the breaker box, electric oven is on same side #7 and 9. Electric cooktop is on opposite site, #8 and 10. So if I turn those off, no bleed?

You found the source, the 220/240v appliances. If your appliances are old a common way of turning off the 220v heating elements was only one side of the 220v was turned off. Therefore, there is power to the elements but since one side is open there is no current flow.

If your really worried then call an electrician and have him or her do a thorough check. Ask around and I'm sure there are some electricians that have worked your neck of the woods for a long time and they'll have knowledge of gremlins of certain homes that were built of your era. Is your home piped with galvanized steel pipe? If it is and a common practice was the neutral/ground connection were connected to the water pipe and from the breaker panel another ground wire was ran to a grounding rod. An good electrician would know if your house has them and would know how to check for corrosion, etc. However, if you did lose your ground reference you would have some other weird problems especially with electronics; it may not be your problem but for a electrician it'd be part of a check list.

https://www.quora.com/Whats-the-electrical-insulation-on-stove-top-heating-elements-made-out-of
 

SDmark

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Many DMM's input impedance can be hundreds of MegaOhms, so you could read a voltage, but there would be no current of any consequence. An old analog meter is likely 20K-ohms/volt. If you do not know what you are doing, either one can give an inaccurate, or misleading reading.
You're saying my $20 Radio Shack multimeter isn't perfect? haha Is there a simple way to measure current? I can say with some confidence that, after reconnecting the wires in the junction box, when #3 is on and #13 is off (so #13 should be reading 43v at the junction box), old incandescent lights in the bedroom do not come on at all. I would think with enough current, a 110v bulb would at least burn dimly at 43v?
 

SDmark

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You found the source, the 220/240v appliances.
Thanks but I think you interpreted my question as a statement. I was asking IF it would stop the bleed IF I turned off the 240v breakers. As I posted later (post #7), I turned off EVERY breaker except #3 and still had 43v across #13.

All the supply plumbing is copper. Waste is cast iron.
 

Reach4

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I added that info to the very first post:

Both breakers on:
Black and red: 241v
Good deal.


old incandescent lights in the bedroom do not come on at all.
If you measure the voltage to neutral in that state , with the dark incandescent lamp providing the load, you will find the breaker to white is pretty much going to be zero. Your Radio Shack multimeter will do that job nicely.
 

SDmark

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So far I have been completely disconnecting the entire master bedroom (load) from the circuit at the junction box, separating the wires and just testing the cable from the breaker box. That's when I get 43v.

This time, with wires JOINED in the junction box, I just turned off #13 and stuck my multimeter probes into an outlet in the bedroom. With all lights off but the alarm clock, clock radio, and a couple USB chargers plugged in, I read about 50 MILLIvolts. When I turned on an incandescent lamp fixture, that dropped to 0 mv.

Hooray! I feel a lot better. In the past in this house, I've found two circuits wired together in a junction box, and another junction box hidden behind a sealed wall, so I get nervous when I come across odd stuff.

Thanks to everyone for your help!
 

Widgit Maker

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a 110v bulb would at least burn dimly at 43v?
No, it will not.
Indications are that you did your voltage checks at the junction box with the wires to the addition disconnected from the wires to the breakers.
If that is true then your readings are a clear indications that you have a damaged cable. Probably a roofing nail making connection between the black and the neutral. When you do a voltage check between two conductors you are reading the difference in voltages on the two conductors. A roofing nail (or some other cable damage) would put a voltage on the neutral but because of the voltage drop across a very poor connection it would not put full voltage on the neutral, nor would it necessarily trip the breaker. A voltage check in such a situation would show a reduced voltage because the you are reading the difference in the two voltages.
You can confirm a connection between conductors by turning off both breakers, set your multi-meter to resistance and do a resistance check between conductors, black and red, black and white, and red and white. If there is no connection you should get an infinite reading. Any other reading would indicate a connection.
Everything you have said indicates a damaged cable.

It might also be informative is you set up a ground wire and did voltage checks between the ground and each conductor. That will give you a true reading of the voltage on each conductor.

If you did not do your voltage checks with the wires disconnected, do so. If you get normal readings, do voltage checks between the wires from the addition. Any voltage between black and white or between red and white going to the addition would indicate that something is being back fed on the neutral from the addition.
 
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SDmark

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Oh man, I thought this was done! Thanks Widget Maker. See post #18 re. how I tested. When breaker #13 is off, there is 43v with no load or 0v with load, i.e. in must be super low current at 43v. Would you still think that indicates a damaged cable? I can test the resistance tomorrow.

Just out of curiosity on the light bulb thing, is that different for DC loads? I'm just thinking how even a weak battery gets a dim glow from an incandescent flashlight or headlight. Or is that more a function of available amps than volts?
 
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