Melted neutral wirenut


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Old 01-12-04, 06:34 PM
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Melted neutral wirenut

My friend plugged in her electric space heater and all of the sudden lost all power in her living room. I traced it down to an electrical box where all the living room outlets came together and found a grey wirenut (about 6 12 guage wires joined) on the neutral that was severely melted.

What are the ramifcations of this? The wiring is fairly new (2-3 years) and appears to be done neatly and correctly. There was an arc fault breaker on this circuit which I replaced with a standard breaker (20A).

Why wouldn't the breaker have tripped on a melted wirenut? Can this happen again elsewhere? What I can I do to prevent this from happenening again?

Thanks
Sam
 
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Old 01-12-04, 07:10 PM
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Portable electric space heaters are inherently dangerous. They use a lot of current, like a hair dryer, but use it for longer periods. They can especially be a problem when used on circuits that have other loads running.

You apparently had a bad connection. Bad connections cause high resistance. High resistance in combination with high current causes high heat. High heat over a period of time causes melted plastic, such as you see, and often fire. You're lucky you only got the former.

The breaker only trips on an overcurrent. A 15-amp breaker adequately protects the proper wire size with well-made connections. But it cannot protect improperly made connections. Less than 15 amps through a bad connection can generate a ton of heat, and the breaker has no capability of detecting heat out in the circuit.

I suggest you put the AFCI breaker back. Why in the world would you want to decrease the protection on a circuit the almost burned the house down once? If the AFCI breaker was 15-amps, then you have committed two serious sins, and have made it much more likely that the next incident will be a fire.

You had one bad connection. This may be the only one, or there may be more. Could be that whoever did the wiring was incompetent, or could be that he just made one mistake.
 
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Old 01-12-04, 07:59 PM
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Originally posted by John Nelson
I suggest you put the AFCI breaker back. Why in the world would you want to decrease the protection on a circuit the almost burned the house down once? If the AFCI breaker was 15-amps, then you have committed two serious sins, and have made it much more likely that the next incident will be a fire.
Thanks for the response. The reason I took the AFCI out is because there was another AFCI in another circuit that had failed. Not knowing much about AFCI's, I posted around and found that they are very troublesome and prone to failure. But I will definitely put it back in place.

BTW the AFCI was a 20A breaker. I replaced it with a regular 20A. You said I committed two sins. Replacing the AFCI was one. What was the other? Should this be brought down to a 15A?

Also, what do you suggest be done about the wiring in the house? Should it be looked over with a fine toothed comb? I would say that aside from the melting of the wirenut, the connection looked fine to the naked eye, so even if I saw this before the melting took place, it wouldn't have raised a red flag.

Sam
 
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Old 01-12-04, 08:30 PM
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Don't overlook the "if" in what you quoted.

What you do now is up to you. I have no data to use to estimate the risk. If you decide to get it checked out, I would recommend a professional.
 
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Old 01-13-04, 07:20 AM
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John, Any thought as to why the AFCI didn't trip on this to begin with? Wasn't this an arc fault? Do they only protect against arcs on the hot side??

I considered replacing some of my standard breakers with AFCI breakers, but the more I hear, the less I consider it. Previously I had heard that they were very prone to false tripping. Now I'm hearing that they don't work.

Thoughts? Experience?

Doug M.
 
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Old 01-13-04, 08:56 AM
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(6) #12's under a wire nut. First of all, the wire nut is assuredly not rated for that many wires, and secondly, what kind of box were these (6) cables in? Wouldn't surprise me it the box was filled beyond capacity as well.
 
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Old 01-13-04, 09:05 AM
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I don't know whether the box was "illegally" overfilled, but I can tell you that it did not seem like it was overfilled. It looked like one of those 4x4 boxes (?) with a mudring reducing it to a standard opening. I had no trouble pulling things out and getting them back in. I didn't even need to use a hammer
 
 

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