Why AC condenser J box wire nuts melted

5 years ago

New Trane home AC condenser J box wirenut connections melted. System ran fine for 12 months after install then began tripping breaker. Inspection revealed melted wirenuts and appears there was arcing in box. Would the aforementioned be caused by loose wire nut connections? Thank you.

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Comments (9)

sktn77a
5 years ago
Possible. Have you checked the current draw?
HU-179123977
Original Author
5 years ago
Hi, and thank you for your reply. I apologize I should have qualified that I’m a home owner preparing for a tech appointment next week to further assess including current draw.
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mike_home
5 years ago
A poor connection has more resistance which causes heating and possible melting of connections. However your circuit breaker was tripping which means the equipment was drawing more current than the circuit breaker rating.

How many times did you reset the circuit breaker? Another possibility is a power surge from an electrical storm could have caused this damage. You also need to verify you have the correct size circuit breaker. The breaker should trip well before connections become hot enough to melt.
mtvhike
5 years ago
I would disagree with your last sentence because of your first sentence!
sandk
5 years ago
Was there a sheet metal screw (instead of a machine screw) attaching the cover plate and causing arcing? That melted one wire nut and took out four thermostats for me. I brought in an electrician who found the problem right away. He’d also seen sheet metal screws used that way before by HVAC installers, it’s what they have handy. Before you settle on a power surge explanation and assume the costs of a repair, make sure the installer didn’t cause the problem. Take some pictures and try posting them on the electrical wiring board.
HU-179123977
Original Author
5 years ago

I reset the breaker 5 times - the max spec on the condenser is 40 and I have a 40 amp breaker. It gets more interesting as I found indications of arcing in the house main breaker panel. Definitely punting this to an electrician but want to be somewhat fluent on possible causes. Thanks to all for input.
User
5 years ago
Can you find the wire gauge?
mike_home
5 years ago
Does the condenser have a service disconnect? If not the electrician should install one while he is there.
HU-179123977
Original Author
5 years ago
There is a new service disconnect with fuses. The disconnect box was installed on the wall about 6 inches away from the J box that contained the melted wirenuts. The fuses inside the disconnect didn’t trip just the breakers. As for the wire gauge, I see one 8 and one 10 inside the disconnect box.