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#57727 - 10/18/05 09:21 PM Expansion coupling...
Attic Rat Offline

Registered: 12/14/03
Posts: 530
Loc: Bergen Co.,N.J. USA
... We're doing a 300 amp. underground service for a residence,and I know that I need to insert an expansion coupling,..but where?? on the line side schedule 80 pvc,just before the meter,or in the trench,...and do I also need one on the load side before entering the basement through the foundation??

I realize it depends on the length of run and the expected change in ambient temperature, but I'm a little fuzzy on where to place it...(don't be funny, I know what you're about to say..)
.."if it ain't fixed,don't break a Licensed Electrician"

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#57728 - 10/18/05 10:07 PM Re: Expansion coupling...
Tesla Offline

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
Fully buried PVC is not prone to expansion issues.

The expansion joint would be needed if the length of exposed run is more than stubbing out to a panel/ meter pan.

Buried runs usually do not have expansion joints since the ground greatly moderates their temperature swings.

#57729 - 10/19/05 05:38 AM Re: Expansion coupling...
winnie Offline

Registered: 09/15/03
Posts: 652
Loc: boston, ma
Hear-say (from the photo discussion area on ECN , rather than personal experience: for a short stub of pvc from underground to the meter pan, the thermal expansion will not be enough to matter. Thermal expansion and contraction shows up as a percentage change in length, so the shorter the 'nominal' length, the smaller the change produced by thermal effects.

However the expansion joint will also nicely accommodate things like the soil settling after construction, or the earth moving for other reasons. If you search in the Photos Submitted for Discussion area, I'm sure you will find pictures of residential service stubs ripped out of meter pans by the ground settling.


#57730 - 10/19/05 07:53 PM Re: Expansion coupling...
resqcapt19 Offline

Registered: 11/10/00
Posts: 2209
Loc: IL
As Jon stated, ground movement is a problem that can be solved by using an expansion fitting and is one method of compliance with 300.5(J).

#57731 - 10/20/05 05:39 PM Re: Expansion coupling...
HotLine1 Online   content


Registered: 04/03/02
Posts: 6792
Loc: Brick, NJ USA

IF you run pvc from meter pan (at house) to pole, & up the obligatory 10'; you need an expansion joint between the ma at the meter pan, and the dirt.

IF you only have to 'leave' a short pvc piece, with the bell/bushing; for BUD direct burial by utility; you do NOT need an exp. joint.

As Jon & Don said....ground heaving, not expansion in this case.

(From another Jersey Guy)



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