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Canada, 120v 60hz

I have two ceiling lights in my family room. Panel supply is in the ceiling to RIGHT LIGHT, with a runner down to the switch. There's a 14/3 wire running to the other, LEFT LIGHT, and the box is also used as a junction to run power further down the chain.

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I recently took down the brick facade on my fireplace, and found, embedded in the concrete, a junction box used to splice wires down to another wall outlet. As I was going to re-bury it, I needed to disconnect these wires. (and run power up from the basement to that outlet).

I followed protocol and flipped the breaker and made sure the lights were off. While I was removing the fixture (LEFT LIGHT) to disconnect the offending circuit, I received a mild shock. I pulled out my tester, and found 120v from white to ground, even though the circuit was off.

Feeling that that famous electrician, Some Genius, had once again been set loose in my house, I decided that it was time to call in a professional.

He arrived the next day and found no voltage on the white wire.

I"m wondering why I found the voltage, and he didn't. Is it possible that CFLs act as a capacitor and can energize a wire for a period of time?

  • Sounds like a standard switch loop. Black down from the light, white coming back. Does that not seem right? Are you sure you had the right breaker? Was the switch on when the sparky did his test? – isherwood Dec 12 '17 at 14:56
  • Yes, that's what it is. But I was working on the other light, that doesn't connect to the switch. (Edit for clarity) – Chris Cudmore Dec 12 '17 at 15:07
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Neutrals are hot anytime a load is connected. That's why we call them "conductors" and insulate them (note this is different than the practice in automobiles). What's supposed to keep them near earth is a solid connection back to the neutral busbar that has much more conductivity than you. When you interrupt that connection, the load will "pull up" the neutral to line voltage, and will place you in series with the load.

The sparky didn't see it, because at the time, the load was unplugged/off.

"But I turned off the breaker!" That particular load was on a different hot circuit, but was stealing neutral from your circuit. This is either a wiring error/laziness... Or a multi-wire branch circuit, whose entire design is to do that. However all legs of an MWBC are supposed to travel in the same cable.

  • Could also be phantom voltage if the OP didn't use a voltage tester that can tell the difference between this and a normally energized conductor. – Jean-Paul Calderone Dec 12 '17 at 16:21
  • Although phantom voltages have no potential, or not enough to feel. I was thinking the same thing at first but think the shared neutral would be a better explanation. – Ed Beal Dec 12 '17 at 20:35
  • A charged input filter capacitor, as suspected in another comment, can sometimes indeed bite you... – rackandboneman Dec 12 '17 at 23:55
  • Do CFLs have capacitors? – Chris Cudmore Dec 13 '17 at 15:28
  • @ChrisCudmore maybe... But they're way too small to bite you, and on wrong side of a rectifier to have any possibility of backfeeding the power line. It's not CFLs. Any other source of back EMF would quickly have that energy consumed by the other loads on the line when you shut off the breaker. These are not loads biting you, put that out of your mind and look for the real problem. – Harper Dec 14 '17 at 0:20

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