Wierd voltages in junction box

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  #1  
Old 08-02-12, 03:11 PM
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Wierd voltages in junction box

I was trying to wire in a transformer to a thermostat. I located a junction box that joins several Romex wires together, including ones coming going to the furnace and other wiring (I believed to some light switches). There were at least four romex cables coming together, with two sets of white-cable joins, and two sets of black-cable joins (using wire nuts).

I got out my voltmeter, picked a likely looking cable, and checked the voltage across one white-black pair. No voltage, though from black to ground I measure 115V, and the same from white to ground.

Hmmmnnn... Let's try one of the other cable joins, that's got to be a junction that's normally live. But, no dice -- same situation.

Anyone have any ideas what might be going on here? I just don't get it, and am trying to avoid tracing out all the wiring coming to this box. Maybe I should just run a separate cable to the breaker box and mount the transformer to its own junction box. But, this one is in just the right location to make it easy to wire to the thermostat...

Any help would be appreciated!

--Brad
 
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Old 08-02-12, 03:15 PM
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including ones coming going to the furnace and other wiring (I believed to some light switches).
Switch loops contain no neutral. If this is a switch loop the white wire may be part of a switch loop and not a neutral.
 
  #3  
Old 08-02-12, 03:28 PM
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Yes, I considered that it might be a switch loop, but it doesn't seem reasonable that there would be two different circuits in this box, and both of them are switch loops. As well, I don't quite see what would be switched from elsewhere and going to this location. I was thinking that the box' wiring might be screwed up, though I think the wiring has been done by capable, licensed electricians.
 
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Old 08-02-12, 03:37 PM
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I was thinking that the box' wiring might be screwed up, though I think the wiring has been done by capable, licensed electricians.
Would it be more reasonable to assume that the "capable, licensed electricians" wired it correctly, and that you just haven't determined the function of the wires yet?

If you think it might help us understand your question, you can post some pictures. See How To Include Pictures.
 
  #5  
Old 08-02-12, 03:46 PM
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OK, fair point. I'll troubleshoot (tomorrow) further and post again!
 
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