circuit blown

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Old 03-23-12, 09:57 AM
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circuit blown

Turned the washer on and it blew an entire circuit (2 rooms). I traced the problem to a box controlling the washer and under/above cabinet lighting. Looks like an arc inside of a wire nut.

Why would an arc occur within a wire nut? The nut was melted and all wires were still within the nut?
 
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Old 03-23-12, 11:32 AM
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xroxer -

You're right. Unless the splice protected by the wire nut failed to the point of losing continuity, there should not be a condition for an arc to occur within a wire nut. My suspicion is that the arc occurred either through the wire nut, if it was worn or otherwise damaged, or out the back of it. The arc could go to the box, if it is metal and bonded to ground, or to the grounding conductors. If you look closely, I'm guessing that you'll see arc-flash burn marks somewhere in there.

That said, killing the power, reworking the splice to ensure that all of the stripped ends are solid, the splice is well-twisted (clockwise) and the splice is trimmed to fit within the proper size wire nut, and that a new, undamaged wire nut is protecting the splice should take care of the problem.
 
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Old 03-23-12, 06:42 PM
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Why would an arc occur within a wire nut? The nut was melted and all wires were still within the nut?
Bad connection between the two copper conductors. Likely what happened was the current from one copper conductor travelled into the steel spring of the wire nut and then into the second copper conductor. The steel spring overheated and melted the plastic wire nut. The spring cuts into and abrades the surface of each conductor, so the current flows freely into the spring when that path to the second conductor has the least resistance. This is very similar to what can happen when a normal wire nut is used on two aluminum conductors or on one copper and one aluminum conductor.
 
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Old 03-23-12, 09:53 PM
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Took it apart. There is no arc flash burn anywhere other than inside the nut. It was definitely an arc as there was a very loud pop and then all power went out.

This nut had 4 14-2 wires (white) in it and it looks liks one of them came loose and pulled down away from the spring/threads. I straightened all the wired out and sanded the arc flash off and put a new nut on and everything seems fine now.
 
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Old 03-24-12, 07:03 AM
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The arcing between the loose conductor and the others was causing the heat to build up and melt the connector. The loose connection was breaking the circuit.
 
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Old 03-24-12, 08:53 AM
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Thank you for coming back to tell us the outcome.
 
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