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Background Info:
I just had about 2 miles of Romex installed in a renovation of an old house. 40 circuits go to the panel. Of these, only 5 are hooked up (temporary basement lighting with flourescent lights, temporary power to three outlets – one on each floor of three story house, and one dedicated circuit for a room that was “electrified” so that it could be used as a temporary office. The other 35 Romex cables are hanging from the basement joist nearest the panel and are waiting to be hooked up to the panel.
Here’s the Puzzler. Using a new Zircon studfinder with live wire detection circuitry, I discovered (to my dismay) that 3 of the 35 wires hanging down near the panel (not hooked up to the panel) are LIVE!!
Using a Volt Ohmeter grounded to the panel ground bus (to be sure of perfect ground) I found that one of the three had 11 volts potential, and the other two were around 5 volts potential.
All conductors in each of the three cables were carrying the same voltage as their two neighbors (i.e. in cable one the black, the white, and the ground each registered 11 volts when compared to the panel’s ground.
OK guys… What’s going on here?
robbwilson
Replies
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(1) Most likely, it's just voltage induced by live circuits run adjacent to the dead ones, just like in a transformer -- "live circuit" detectors are easily deceived by this, and Romex does nothing to shield the conductors from electrical fields; (2) it could be wiring error where two circuits are joined to one another through a load, or a ground fault, or other miscellany. (1) is most likely, and involves no danger because the current it could deliver is tiny, but don't take any chances if you're unfamiliar with electricity. You might take a look at whether the suspicious cables run near the officially live ones.
*I think andrew hit the nail right on the head.Current traveling through a wire creates a magnetic field that can cause voltage or current in any conductor placed too close. Don't worry about it.Another possibility is that your hanging cables are already grounded and their neutrals are tied into the neutral bus bar. If this is the case, current traveling through appliances on your live circuits has to travel back to the breaker box on your neutrals. Anything attached to this bus bar will measure slightly highter than zero volts most of the time. eleven volts is more than I would have expected but meters can be off alittle too.
*I would say with 90% certainty that it is an induced voltage like andrew said. If it was me I would probably touch the wires with the back of my hand to see, but then again I'm not real bright. I DON'T RECOMMEND THIS! You could use your meter to test amperage to see if it's anything significant.
*Nick: I always just grab em, too. But always remember to put one hand on your butt.
*I seem to recall some code language about how tightly bundled romex could be and I wonder if this symptom and your description indicates that you have a lot of conductors bundled tightly together. I believe the code restrictions is because of heat, not induced currents.
*I remember when I was a youngster (around 13 or 14) and a buddy and me decided to go down in the woods near the Railroad tracks to pull down some wire from an old set of "phone" poles. About 8 poles in a row, wires cut off at both ends. Grabbed the first line and it shocked the piss out of me! I looked over the set of wires again to see if they were tied in somewhere but they weren't. Then I realized there was a set of high tension lines running overhead along the side of the tracks. Obviously this was the same situation as this post presents but on a larger scale. This post reminded me of it so I thought I'd waste your time with it.Pete Draganic
*I agree with all that said induction from close proximity of wires, although it is really induced current, not voltage per se. When measuring the voltage with a modern digital voltmeter (or multimeter), the exteremely high input resistance of the meter lets the very small induced current show up as a voltage. Older analog meters did not do this as much. Also, if in doubt, use a small light bulb tester on the cicuit (which has low resistance). If it lights up, the circuit is truely hot.Regards, Steve Wright
*Just out of curiosity, would armored cable or rigid conduit also induce current under similar circumstances, or would the outer metal sheath act as a shield?Also, are there implications for how far apart cables should be placed?
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Background Info:
I just had about 2 miles of Romex installed in a renovation of an old house. 40 circuits go to the panel. Of these, only 5 are hooked up (temporary basement lighting with flourescent lights, temporary power to three outlets - one on each floor of three story house, and one dedicated circuit for a room that was "electrified" so that it could be used as a temporary office. The other 35 Romex cables are hanging from the basement joist nearest the panel and are waiting to be hooked up to the panel.
Here's the Puzzler. Using a new Zircon studfinder with live wire detection circuitry, I discovered (to my dismay) that 3 of the 35 wires hanging down near the panel (not hooked up to the panel) are LIVE!!
Using a Volt Ohmeter grounded to the panel ground bus (to be sure of perfect ground) I found that one of the three had 11 volts potential, and the other two were around 5 volts potential.
All conductors in each of the three cables were carrying the same voltage as their two neighbors (i.e. in cable one the black, the white, and the ground each registered 11 volts when compared to the panel's ground.
OK guys... What's going on here?
robbwilson