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Posted By: WNYJim underground conductors failed in RMC - Why? - 05/06/08 10:47 PM
Four years ago I had a call for a free standing meter station that had lost one hot leg.
The 100A supply came down a pole, underground (about 10') and up to the meter channel.
Pulled the wires out and found one of the aluminum conductors was completely separated. The insulation showed no sign of failure (other than some melting right at the break) and the conductor had some oxidation at each open end.
Pulled in new URD and all was fine.
This spring I got a call that it happened again.
So this time the RMC was removed and replaced with PVC.
The break occured in the same spot as before. The conduit was inspected for sharp edges or anything that could have caused this failure.
Just like the first time the wire showed no sign of damage (nicks, cuts, scrapes).
There is very little load on this, it only feeds a 150 watt spot light and a 1/4 HP pump.
The original feed lasted 40 years, the second only 4.
Any ideas?
Posted By: LK Re: underground conductors failed in RMC - Why? - 05/06/08 11:01 PM
We found like that, turned out the homes were moving away from the street, the homes were built on steep hills, and were falling away from the road, pulling the wire apart.
Is this in an area that has frost and is the conduit below the frost line? I have seen conductors damaged when the water in the raceway freezes and crushes the insulation.
The break was in the section underground.
The soil is all sand and no strain was found on the wires.
The wires had a nice loop in the meter channel and on the pole there was plenty of slack.
I'm stumped!
Frost can play havoc with a pipe full of water?? What about road salt?? and a knick in the insulation
It could have been frost but we didn't see any damage to the other wires.
This is located about 100ft from the road and the coduit was in good shape.
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