Long post, because I'm not sure what information is critical. The ultimate question is what, if anything, I need to do to ensure there are no hazardous conditions in my home.
Friday night, the lights flickered for 10 seconds and then the house lost power. (Mostly, it turns out.) No other house on the block lost power. I went out to the service panel. I could see the meter was not on.
When I touched the service panel, I got a shock and dropped the door. I got my no contact tester (not a volt meter but the light up stick) and it lit up and beeped when I touched the panel box. I turned the main breaker off with a wooden spoon. I touched the box again and it again showed voltage even with the main breaker off. I then started testing other things. It lit up on the ground wire. It lit up on the hose bib. I yelled into the house and told everyone not to move. I tested the door handle and it was ok. I got everyone and the dog out of the house and into the car for warmth and called the power company.
I went back in with the tester, testing everything before I touched it. Pretty much every thing I tested in the house that was connected to the electrical system showed a positive test. The outside of the metal oven. The frame of the tv. Metal lamps (the actual lamp, not just the cord.) A laptop that was plugged in (the laptop itself.) Each switch cover. Most peculiar, low power led lights in our range hood were on at about 20 percent their usual strength. (They are not on a batter back up.) The GFIs in my kitchen were tripped, but their lights were on, showing red (not green, as usual). The refigerator was getting some power, very weakly.
The guy from the power company got there a few hours later. He was initially confused about what was going on. He asked whether we had any solar or batteries or generators that could be "backfeeding" the electrical system. (We don't.) He unscrewed the lines feeding the house from the meter. As soon as he disconnected the last of them, everything stopped testing positive with the non-contact voltage meter. The lights in the stove went out. He tested each of the wires that were coming in from the street, which had been disconnected from the meter. It appeared to me, but I'm not sure because I was standing a respectful distance away, that he got a voltage reading on the neutral. He said it appeared that the buried cable coming in from the street had degraded or been damaged and that the "hot must have nipped the neutral." I wanted to ask more, but I also wanted to let him do his thing.
He ran a temporary above ground cable that restored power and said the company would install a new underground cable from the street this week. He cleared us to go back in the house. I tested things with my voltage meter and it was all ok. Everything was working fine, except the high speed internet. The guy from cox came yesterday. He found that the connector from the box across the street, which feeds the line to my house, was completely fried and melted. He said he had never seen that, but that it had "done its job." I think he was saying that the coaxial cable is grounded at my house and so current must have zapped it along the ground? I don't really understand. I looked at where the coax enters my house and there is a box on the outside of my house with a ground wire that comes out of the box and is clamped to a copper water line.
Anyway, seeing the melted cable freaked me out a little.
I did a bunch of reading on what could cause a house to have power if the main breaker is off. None of it makes sense. And how would my copper plumbing show positive? And why didn't any of my breakers trip?
Let's say that the insulation between the hot and neutral wore out beneath the ground, feeding my house. Could this explain it? That would put current on the neutral coming into the house. Could that serve as power to everything the house and the grounding system that flows independent of the breakers? Why wouldn't that be a short circuit that would trip a fuse or breaker in the transformer box at the street?
Anyway, the "why" is less important to me than understanding if there are likely to be unseen dangers in the house as a result of this incident and what, if anything, I can do about that. I guess the power company guys will be back to re-install cable to my house and I can ask them, but I'd like to be educated. I can't find anything like this on the internet. Many thanks.
Best Answer
I think the power guy's assessment was spot-on
What was happening is that the incoming hot probably contacted the ground indirectly via the insulation failing in some fashion. Your neutral bonds with the ground in your main service panel, and are fed into a series of grounding rods near your panel. As such, your panel and all electrical switches and receptacles attach to this point (via grounding wire) and the powerful draw of the service neutral prevents it from flowing through you instead (which is why you don't bond ground and neutral anywhere else).
What it sounds like is that the shielding on the incoming service wire degraded and was able to put that power into the ground nearby, which was then picked up by the grounding rods (this process would be amplified if the ground was wet from recent rains). This then reversed the process, where your ground and neutral now became live. This is evidenced by
It wouldn't hurt to have an electrician come out and inspect the panel. I wouldn't open a main panel myself, since the incoming hots from your power company cannot be turned off by you (that main breaker just cuts power to the rest of the panel). Specifically, make sure nothing in the panel was damaged, and that the ground and neutral bond look OK.
Next, take your contactless tester and try them against a ground and neutral wire. You shouldn't get any reading from them (unless electricity is flowing through your receptacle from a downstream source). A wiring tester would also help in this case.
Once the power company has permanently replaced the wire, you should be just fine.