ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#177543 - 05/06/08 03:47 PM underground conductors failed in RMC - Why?
WNYJim Offline
Member
Registered: 06/06/02
Posts: 39
Loc: Rochester, NY, USA
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?
Top
Work Gear for Electricians and the Trades
#177544 - 05/06/08 04:01 PM Re: underground conductors failed in RMC - Why? [Re: WNYJim]
LK Offline
Member
Registered: 01/21/03
Posts: 1429
Loc: New Jersey
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.
Top
#177545 - 05/06/08 04:29 PM Re: underground conductors failed in RMC - Why? [Re: LK]
resqcapt19 Offline
Member
Registered: 11/10/00
Posts: 2148
Loc: IL
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.
_________________________
Don(resqcapt19)
Top
#177546 - 05/06/08 04:31 PM Re: underground conductors failed in RMC - Why? [Re: LK]
WNYJim Offline
Member
Registered: 06/06/02
Posts: 39
Loc: Rochester, NY, USA
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!
Top
#177548 - 05/06/08 05:40 PM Re: underground conductors failed in RMC - Why? [Re: WNYJim]
walrus Offline
Member
Registered: 07/25/02
Posts: 680
Loc: Bangor Me. USA
Frost can play havoc with a pipe full of water?? What about road salt?? and a knick in the insulation


Edited by walrus (05/06/08 05:41 PM)
Top
#177553 - 05/07/08 02:54 AM Re: underground conductors failed in RMC - Why? [Re: walrus]
WNYJim Offline
Member
Registered: 06/06/02
Posts: 39
Loc: Rochester, NY, USA
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.
Top

Member Spotlight
Member Since: 11/17/00
Posts: 2232
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 52 Guests and 8 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
Freecrowder, clee512, Jdscott2005, FAIZAN, Regitest2

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals