Pulling thru PVC

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Old 06-21-12, 09:32 AM
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Pulling thru PVC

I need to pull 3 #12 THWN conductors thru 170' of PVC. No bends. Should I use 3/4" or go with 1" PVC?

I am thinking maybe adding an expansion joint because this PVC will emerge from the ground and be exposed to the air. I don't want the conduit under tension.

Thanks
 
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Old 06-21-12, 10:14 AM
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If it's not buried yet, I'd go bigger just in case you might want to put something else in there down the road.
 
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Old 06-21-12, 10:29 AM
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I am thinking maybe adding an expansion joint because this PVC will emerge from the ground and be exposed to the air. I don't want the conduit under tension.
You can add one (or one at each end) where the conduit emerges from the ground, if you're concerned about frost heave. Expansion joints cannot be buried, SFAIK. Not sure why this would be an issue in NC.
 
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Old 06-21-12, 11:32 AM
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About 70 feet of the conduit will be buried. The other 100 feet emerges from burial and will be fastened to the underside of a pier. It will be out of the sun but get hotter than what is buried.
I looked at the tables and found 100 feet of PVC will expand 1.8" for a 50 degree temp change.
That's why I think an expansion joint would be a good idea.

I plan to run a 3/4" PVS water pipe adjacent. That one will see even more movement I would think as cold water moves in to replace water sitting in the pipe. But that is an issue for the plumbing side.
Thanks!
 
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Old 06-21-12, 01:48 PM
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I would add one expansion coupling underground (depending on the distance of the run) because of ground movement. And yes, expansion coups are a good idea (for above, and underground use). PVC doesnít look pretty after much heat has hit it. Iíve seen houses with spaghetti-like pvc.
 
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Old 06-21-12, 02:12 PM
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one expansion coupling underground
Hey, have you got a link to one of those? I've never seen one, and I'd like to see what it looks like.

Yes, expansion under the pier might be a good idea. The main thing I would be concerned about is installing the pipe hangers in a way that will allow the pipe to move through them easily.
 
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Old 06-21-12, 03:38 PM
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I would think the dirt would settle around the expansion coupling and cause it to stop working.
 
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Old 06-21-12, 03:50 PM
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I would think the dirt would settle around the expansion coupling and cause it to stop working.
Per engineering specs it works!! Also itís required depending on the jurisdiction, and installation. Some jurisdictions require it underground to keep the risers from pulling off the wall.
Hey, have you got a link to one of those? I've never seen one, and I'd like to see what it looks like.
Iím surprised you haven't seen one!! This could mean either your area doesnít require it, you havenít done any underground work that required one, or your areas AHJ donít care.
hereís a link:
Expansion Coupling, 2 Piece, 4 In, PVC - Conduit Fittings - Conduit Fittings - 4FYA2 : Grainger Industrial Supply
 
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Old 06-21-12, 03:53 PM
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I guess i should add. Like anything, you must install them correctly, or they want work as manufactured.
 
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Old 06-21-12, 04:33 PM
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I would think the dirt would settle around the expansion coupling and cause it to stop working.
So would I. Interesting reading online:

INSTALLATION RECOMMENDATIONS
ē When expansion joints are used in a vertical position, the piston should be mounted in a downward position so dirt cannot deposit between the barrel and piston at the muzzle of the expansion joints.
Source: Scepter Rigid PVC Conduit & Fittings Catalog

"PVC expansion joints are intended to be used for thermal expansion of the PVC conduit only. They are not (and never were) intended to be used to compensate for trench settlement. When the PVC expands and contracts due to thermal forces only, the wire does not move. The conduit just expands and contracts. So, in short, using a PVC expansion joint to compensate for trench settlement is an 'off label use' for these fittings, and they aren't specifically intended to be used in this manner. It seems it would be better to do without them, unless there is a place to leave slack in the wire (which there normally isn't)."
Source: Contractor Talk
 
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Old 06-21-12, 04:42 PM
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Here is the one I plan to use. Thomas & Betts (Carlon). About $15 or so.

http://www-public.tnb.com/ps/fulltil...cgi?part=E945E
 
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Old 06-21-12, 04:51 PM
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Iím surprised you haven't seen one!! This could mean either your area doesnít require it, you havenít done any underground work that required one, or your areas AHJ donít care.
hereís a link:
Expansion Coupling, 2 Piece, 4 In, PVC - Conduit Fittings - Conduit Fittings - 4FYA2 : Grainger Industrial Supply
The total length of direct-burial pipe I've installed is probably measurable in miles and, on any given day, I may be in one of two dozen or more jurisdictions. I've never installed nor seen a buried PVC expansion joint. And, as far as I can tell, I still haven't. I may have missed it, but I didn't see any reference to direct burial at the link you posted.

So maybe all two dozen of our local jurisdictions "don't care?" And none of our customers, including the high-tech companies and the defense contractors and their clients, who often do their own independent inspections around here, cares either? It just doesn't seem likely, somehow.

The only time I remember installing PVC expansion couplings was in a multistory parking garage, where the runs were crossing the structure's expansion, or seismic, joints. And that involved building a slack box to avoid compromising the conductors, since we weren't working to compensate for thermal changes (although they did that too).
 
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Old 06-21-12, 11:35 PM
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I guess I can agree either way. This is a topic of discussion (Not debate)-- where most are favoring ground movement as a reason. But others are highly in favor of the coupling being above ground as required by some serving utilities. Some jurisdictions may only require a ground loop. I most certainly agree about the expansion and contraction note!!! Good post from you guys
 
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Old 06-23-12, 01:43 AM
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Well Nash installing expansion couplings has been "code" for at least 10 years,
 

Last edited by ray2047; 06-23-12 at 07:05 AM. Reason: Unnecessary comment removed, original archived
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Old 06-23-12, 09:48 AM
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Due to ground temps not varying much 18" down in your area, I would not put an expansion coupling in the ground. I would only install it in your above ground run.
 
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Old 06-23-12, 10:36 PM
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rich3236, see PM .
 
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