Today I opened up a panel and I saw a 12 awg neutral wire was very melted. I expected to see that a multiwire branch circuit had been miss wired but after tracing the wire back to the nm cable I saw that it was just a single wire circuit. The hot leg of this cable looked fine. I was wondering what would cause this to happen to only 1 conductor out of 20? I'll be going back next week to investigate more, after the homeowner takes down some sheetrock to expose some burried boxes! :-O In the meantime I disconnected the circuit from the breaker and I unconnected the neutral. Any Ideas?
I am thinking (especially with you mentioning buried boxes) that the neutral may possibly have been commoned with other neutrals in one of the boxes, thus acting as the return for other circuits too. It's at least a possibility.
Re: What would cause this?#52241 05/23/0505:11 PM05/23/0505:11 PM
I'm with chipmunk on this. Although you see a 2-wire in the panel, it could be carrying 2 or more loads. Especially bad if they are the same phase. Good way to find out is to put an amp-clamp on it, check the load amps, shut the circuit off, and check again. Another is to shut the whole house off, and ring it out through all of the other circuits with the neutral disconnected. In both ways you could still miss it if the load were not on. The sure fire way is to follow it.
Other possibilities could be, and should not be ruled out, is that the breaker is bad, and it fed several space heaters for a while without tripping. The circuit could have a history of abuse, reset and trip cycles, or one big short in the past. Bad connection further in the circuit, or just plain dirty wire. (Dissimular metal, or chemical reaction, or low grade copper, or buss material.)
Mark Heller "Well - I oughta....." -Jackie Gleason
Re: What would cause this?#52242 05/23/0506:57 PM05/23/0506:57 PM
Thanks Chipmunk and e57. I hope I'll see the problem when they open up the ceiling. I told the home owner that since the neutral was melted in the panel, that we could assume that it is melted in other parts of the circuit also. My thoughts are leaning towards finding some neutrals from different circuits tied together. Thanks again.
Thats how we do it up in the woods!
Re: What would cause this?#52243 05/23/0508:59 PM05/23/0508:59 PM
I would add that if you would clamp around both the ungrounded and grounded conductor at the same time and the meter reads anything besides zero, we would have a problem if it was suspect of being a two wire circuit.