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#53542 - 06/28/05 01:32 PM Expansion couplings for PVC service
poorboy Offline

Registered: 06/02/05
Posts: 128
Loc: Central Maine
When am I required to use PVC expansion I need them for the service I described in the PVC Service thread? I always use them at residential services on poles, but here I have block buildings and the 4" conduits come out of well compacted asphalt over gravel parking lot.

By the way, yes, I do have a code book...but you guys are just so darn accomodating.(LOL) Thanks for the input!

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#53543 - 06/28/05 05:50 PM Re: Expansion couplings for PVC service
Larry Fine Offline

Registered: 02/18/05
Posts: 684
Loc: Richmond, VA
Without looking it up, my instincts say only when crossing a structural expansion joint, or other joint subject to movement.

But then, I've been known to be wrong.
Larry Fine
Fine Electric Co.

#53544 - 06/28/05 06:11 PM Re: Expansion couplings for PVC service
poorboy Offline

Registered: 06/02/05
Posts: 128
Loc: Central Maine
I should clarify that I live in Maine and we use them when we think frost will move the ground a few inches. This solid compacted gravel seems unlikely to move a whole lot, however.

I have repaired meter trims that had 2" PVC driven up into the trim an inch by the frost action(Popped the concentric KO's right out) in mobilehome services on a pole.

#53545 - 06/28/05 06:40 PM Re: Expansion couplings for PVC service
HotLine1 Offline


Registered: 04/03/02
Posts: 6792
Loc: Brick, NJ USA
My NEC is in my truck, but...
Any PVC exiting the ground should have an expansion joint.
Ground heaving and/or settlement causes a lot of damage.

Also, 'runs' of PVC on roofs, walls, etc., require exp. joints. There's a table in the Carlon catalog giving requirements, with amount of expansion, etc.

As said above, in large buildings, where there are structural expansion joints, it is required to install expansion joints on ALL raceways. (PVC, EMT, GRC, etc)


#53546 - 06/28/05 06:50 PM Re: Expansion couplings for PVC service
PCBelarge Offline

Registered: 06/08/03
Posts: 657
Loc: Dobbs Ferry, NY, USA
In Maine you definitely need to be concerned about ground movement due to frost heave. 300.5(J) is the reference and you will need to use one of several approved methods.
Of course this is for conduit that is coming up from under the grade.
Read the FPN following this section.
Pierre Belarge

#53547 - 06/28/05 08:41 PM Re: Expansion couplings for PVC service
renosteinke Offline
Cat Servant

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Fascinating! I never thought about frost heave. I am lucky to live where the winters are somewhat milder than they are in the "rust belt," and our ground doesn't have much moisture in it to freeze- so it's not an issue here.
(Of course, the downside is you almost need dynamite to place a ground rod!)


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