Voltage puzzler

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jeff43222

Senior Member
The other day I was called to a guy's house to troubleshoot the outdoor light over his front door. When I opened up the fixture, there were two black wires entering the box, one connected to the fixture's black wire, and the other connected to the fixture's white wire. No ground wire anywhere. Yep -- another handyman's special.

One conductor showed 117 volts to ground. The other one showed about 20 volts to ground. Between the two conductors was about 40 volts. I was able to trace the ungrounded conductor back to the switch box, and it was connected properly. As far as I could tell, the mystery conductor was connected to the switch's grounding screw (??). Additionally, entering the switch box with the two aforementioned black wires was a white wire. I have no idea what it might be connected to. I moved the mystery conductor from the ground screw and twisted it together with the grounded wires inside the switch box to see if that might fix the problem, but it had no effect.

The boxes in question are metal, and they are bonded somewhere along the line. Also, there is some kind of unknown metal raceway between the switch box and fixture box (it looks like it might be old FMC or something like that).

I've already told the guy it needs to be re-wired, and he's fine with that. I'm just wondering if anyone has an idea as to how I'm getting odd voltage readings on the mystery conductor. At this point I'm thinking magnetic inductance, but I'm not sure.
 

racraft

Senior Member
Re: Voltage puzzler

The funny voltages are because the neutral is open somewhere in the circuit.

Do not be so quick to blame a "handyman special". Many old wiring jobs have unusual connections or parts because that's just what was done years ago.
 

jeff43222

Senior Member
Re: Voltage puzzler

This one was definitely a handyman's special. The mystery wire was very new-looking THHN/THWN, and the light fixture box had new mounting straps in it. Some work had been done on this light within the last few years, and it was done with several obvious code violations. I have a hard time imagining a pro doing such a poor job. I guess anything's possible, though.
 
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