[masraum]

Originally Posted by jyl

I found the main shutoff, it is on the external panel (?). I’ll post a pic later. So no hot swap needed.

The breaker I was replacing is not defective. There is a short somewhere in the circuit.

The circuit involves 1) the ceiling light which has two NMC cables (call them “A” and “B”) which I recall were connected and the old light pigtailed off the junction (I’m replacing with canless), 2) the light switch on the wall a few feet away, 3) an outlet on the wall directly below the light switch. That’s all the stuff that doesn’t work when the breaker is tripped.

When I connect the two NMC cables (black to black, etc) and the new light, the breaker trips. When I delete the light, the breaker trips. When I disconnect the “cold” cable B, and connect just the “hot” cable A to the light, the breaker does not trip, the light works, the outlet works, but the switch does nothing.

Hmm. I had assumed the outlet was wired to the switch (lots of weird stuff like that here), hot cable A came from the switch and powered this light and something else further down the line via cold cable B. But no.

Well, this is a mystery. I haven’t given it more than 5 minutes’ pondering, so not sure if it is a deep mystery or I’m just stupid.

Worst case, the light will just be on 24/7 until my electrician comes in a couple months to do a bunch of work and she can sort this out. We leave lights on at night anyway, to signal to would-be squatters that the building is not vacant.

Originally Posted by Dpmulvan

Neutral isn’t always necessarily cold in a switch loop.

That's what I was thinking. There are all sorts of ways that it could be working safely. There are things that should be done to ensure that someone coming along after the fact has a clue, for example, you could have a white wire that needs some black tape as a clue that it's actually hot. It's always a good idea to have one of the sensors that tells you when a wire is hot too. Try to figure out where the power is coming into the circuit (at the outlet, at the switch, at the overhead light fixture, and hook up one wire at a time in series until you complete the circuit.