How can I determine which neutral in a sub-panel is for a particular (tripped) breaker?
We have a sub-panel in the basement for circuits that are supplied by an automatic generator. There are eight breakers in that box, and seven neutral wires on the bar, none of them labeled. (I think one slightly larger wire is for a ganged pair of breakers.)
I've tried disconnecting several of the wires, one at a time, but when I try to reset the breaker, it trips again. Could it be shorting to the bar in general, rather than to its associated neutral? I think there may be a hot-to-neutral short somewhere in the circuit, but I need to isolate the correct neutral before further testing.
Something tells me it could involve shutting off all eight breakers in that box, and maybe disconnecting the generator so it doesn't fire up (or at least not supply any juice) when I open the main breaker.
Best Answer
You should disconnect all power to your sub-panel (turn off your main breaker and your generator). Be absolutely sure the power is off to avoid serious injury or worse. I'd suggest using a voltage sensor pen to verify the panel is cold.
You will need a ohm/continuity meter for this test.
Pop the breaker in question out of the panel, leaving the hot wire connected. Turn on the breaker and test continuity between the back of the breaker and the neutral bus. Since the breaker is tripping, you should see continuity/low resistance. If you do not, it's possible the short only exhibits under higher voltage but more likely, you have a bad breaker.
Assuming you do see continuity, remove neutral wires one at as time from the bus and recheck continuity. When you lose continuity, you just removed the neutral you're looking for.