I thought I submitted this question, but it doesn't seem to have gone through. I'm trying it again...

Hi, folks!

I hope someone can help me out with a weird electrical problem I'm having. I'm a pretty experienced do-it-yourselfer, and have tackled some pretty major home electrical projects. However I have just run into a problem, doing something that should have been very simple, that I've never encountered before.

I'm installing a new wall switch for a sconce. It's an old house, so it's often difficult pulling the wires through the plaster/wood-lathe walls, under sub-floors, etc. But, thank God, I've managed to get that part done. I set up the new wiring, but didn't connect it yet. I disconnected the sconce from the existing wiring with the breaker turned off, but then I had to turn the breaker back on to test which was the hot and which the neutral wires of the circuit. Like I said, it's an old house and a lot of the wiring is the old cloth covered type which is not color coded. Whenever I do any work on the old wires, I have to test to see which is hot and which neutral. In any case, I flipped on the breaker and tested, and found the hot wires (there are three wire pairs running through the box where the sconce is located, feeding various other lights and outlets throughout different parts of the house). But then I noticed that several lights that should have come on when the breaker was flipped on, did not. As I checked around, I also noticed that several of the outlets on that circuit were suddenly testing "hot/ground reverse" whereas before they were all okay.

I don't understand what's going on, since I didn't change anything on the circuit. All I've done up until now is take the sconce wires off the circuit and run some new (dead) wire through the box without connecting it. What could cause this kind of problem? Is it possible that while I was pulling the new wire (Romex) through with my electrical snake, one of the existing wires broke? It is pretty old wiring and on occasion I've run into some wires that have become a bit brittle. Would that account for the sudden "hot/ground reverse" problem and the fact that some of the lights are no longer working?

I'd appreciate any advice on this. It's pretty urgent, since this is one of the main circuits for the house, and I now have no lights in my kitchen and living room.

Thanks.

This is not my area, but since it's "urgent" I'll post a theory until TK can get here with the real information.

It sounds like your two circuits have a shared neutral that was disconnected. Hopefully it just comes from when you disconnected the wires at the switch and the sconce, rather than a broken wire from the snake. Reconnect everything the way it was before you changed anything, check all of the other connections in the same box, and cut the power back on. See what works.

Thanks for the quick answer to Ceilingfanrepair. As it turns out, I solved the problem. It was exactly what I suspected - a broken neutral wire. Luckily it was inside the box, covered with layers and layers of dried out 50 year old electrical tape. Once I sorted through the wires and got the tape off (had to use pliers, it was so bad), I found the broken wire. Luckily there was enough of a nub left for me to splice into, so everything's working again. Would love to change those wires, but that would be a serious job with major wall damage, etc. At least it's working again.

Thanks!