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Joined: Jun 2005
Posts: 124
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poorboy Offline OP
Member
When am I required to use PVC expansion couplings...do 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!

Joined: Feb 2005
Posts: 693
L
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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.
fineelectricco.com
Joined: Jun 2005
Posts: 124
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poorboy Offline OP
Member
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.

Joined: Apr 2002
Posts: 7,274
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Poorboy:
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)

John


John
Joined: Jun 2003
Posts: 681
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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
Joined: Jan 2005
Posts: 5,316
Cat Servant
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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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