Conduit Acting as Neutral?

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  #1  
Old 02-21-14, 11:19 PM
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Conduit Acting as Neutral?

I searched the forum and only found a one thread about this, but I need a little more detail in isolating the problem.


http://www.doityourself.com/forum/el...ml#post2237584

In hopes that the original poster might get notified of the very late reply I posted the following to that old thread:



I have this same problem, I can literally power a pigtailed light bulb from any hot wire to the conduit, or junction box in the system. The conduit reads 125V on the voltmeter from every wire (14 ga) to the conduit.

I'm in Canada. The townhouse is from the late 60's. Ungrounded 2 wire (thhn) throughout the unit with mostly 1/2"emt, some larger emt from the panel to the first junction box and to the 220V outlets.

There are some very, very busy (probably too busy) junction boxes with 12 or more wires nutted together. 90% of the lights and outlets on 2 15A circuits.

The previous owner has made some additions with BX and romex, one gfci breaker that used to be for a jetted tub, but I've deleted it.

What's the first step in isolating and locating the short?



Thanks for any help!
 
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  #2  
Old 02-22-14, 04:44 AM
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As the others have asked in the other thread, what gives you the idea you have a "short"? Neutrals and grounds are potentially the same. Your conduit is your ground. A light bulb will illuminate if you cross it with the hot and grounded conduit. What specific problems are you having?
 
  #3  
Old 02-22-14, 10:20 AM
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How the problem first presented itself:

I'm renovating the kitchen and bathroom, the walls and ceilings are exposed. To change the location of the bathroom ceiling light, which is the terminal end of this particular branch, I deleted the conduit and 2 wire thhn, attached the 14/2 in the next-to-last junction box, attached the bare wire to the box and ran the 14/2 to the new octagonal box light location. With the breaker off for what I expected to be the light circuit, I got a bit of a tickle from the bare wire when I was stripping the hot. It's live.

The breaker trips if the bare is attached to the box and the new light is on, and does not trip if the bare is not attached and the new light is on.
 
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Old 02-22-14, 10:26 AM
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It sounds like you have a short at the light end where the light itself is causing the short to ground.
Disconnect it from the circuit to confirm.
 
  #5  
Old 02-22-14, 10:42 AM
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The conduit should already be grounded to the box where it originates. I agree that 8t sounds like this is in the new wiring.
 
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