I had a breaker that tripped and would not reset (after turning off). The circuit contains some garage lights, outdoor lights, canister lights inside, and two plugin receptacles. I've done a lot of hunting, and isolated the problem.

The canister lights are controlled by two 3-way switches and a 4-way in between. With those switches disconnected, the breaker will reset and everything (except the canisters) works fine.

So I replaced the first 3-way with a simple switch, and the breaker will reset. Everything including the canisters works fine. So I have isolated my problem to the runs beyond that first 3 way switch.

The run from the first 3-way to the 4-way is very short. The switches are only 7 feet apart in my house. The Romex (3wire plus ground) runs up into the attic and back down to the 4-way.

I disconnected all four wires on both ends of this run of wire, and here's where I'm stumped: I can use a continuity tester on both ends of the wire easily, since they are so close together. I obviously get continuity when i connect Red-Red, White-White and Black-Black. But I don't get continuity connecting Ground-Ground. I DO, However get continuity between the a black end and the opposite ground end.

Somewhere in between, the ground has to be in contact with the black wire, and completely broken from itself because of the lack of continuity with the other ground end.

No new pictures in the walls, or other disturbance. The house is 10 years old. We were gone from the house during the day when the breaker first tripped, it was raining very heavily (which led me to suspect the outdoor fixtures first ----lots of time wasted there).

I spent a significant amount of time in the attic and located where this run comes up from the 3-way, and back down to the 4-way. No damage to the wire in the attic. It has to be one length of wire.

A couple questions:
1. If my diagnosis is correct (black wire contacting ground wire - and ground wire not continuous for the 25-30 foot run), how in the heck could that have happened?

2. If I can get past the scientific curiosity of "how did this happen" and actually try to fix it - can I just run another length of Romex and leave the old wire in the wall? I assume it's stapled to the studs so I won't be able to pull it out. I can get a fish tape and should be able to put a new run in, no problem. But obviously I won't be able to affix the new wire to the studs without cutting and patching drywall....I'd rather not do that. Can I leave the loose wire in between the studs? I've got 10 foot ceilings in this room, so there is about 6-7 feet of wire between the switches and the attic.

Thanks for reading all the way through this. I've been testing, thinking, and reading posts online for 5 days now. Any advice is appreciated.