My wife and I were sitting at the kitchen table and heard about 10 seconds of buzzing, then smoke came out of the GFCI next to the kitchen sink. Nothing was plugged into the outlet, and the only thing on was the dishwasher, which after inspection was sharing a neutral with this outlet, but the dishwashers hot was on another circuit. The breaker did not trip either. The receptacle is about 2 feet to the left of the sink and about 8 inches up from the counter. Here a picture of the damage:
I called an electrician neighbor and he spent a long time with me trying to figure out what happened. We took out all the receptacles in the kitchen and tried to make a circuit diagram. I drew it out after he left and I apologize for anything that is not correct, but here's what I got:
So the receptacle in question is a split, where the neutral is shared with a circuit on the other leg in the house. Since neither breaker tripped, they were both replaced as a precaution and tied together. I also replaced the GFCI outlet on the other side of the sink that is sharing the neutral wire.
I couldn't even find anything else on the same circuit as the one that burned, just the one receptacle. I replaced it with a non GFCI outlet, as I didn't have another one on hand. I guess I'll need to pick up another one and swap it out. I did add a pigtail to both the neutral and the hot lines for that outlet, but everything else I left the same.
The insulation on the wire seemed good (after the burned part), so I trimmed the wire back and used it. The electrician said that the outlet must have just gone bad.
Everything is hooked up and working right now, but I'd love some insight. It's hard when you don't have confidence your house won't start on fire while your sleeping.