Long PVC Runs

[Energy-Miser]

I believe that the code requires use of expansion joints whenever there is possibility of 1/4" or more of thermal expansion in conduit runs. I have found expansion joints for pvc that works just fine, however my question is about the right choice of straps to allow for movement of the conduit, but not be too loose, causing problems at the time of wire pull. Anyone have good/bad experiences with this? Thanks,

 

[Energy-Miser]

Can I bribe someone into a reply?

Can I bribe someone into a reply?

Appreciate your inputs. E/M

 

[Pierre C Belarge]

First I would like to point out that there are jurisdictions that do not permit metallic straps, and one is to use PVC straps.

I think the 2-hole straps allow movement for expansion and contraction, and still provide good support of the raceway.

 

[jackbenny]

use approved straps but contact the manuf. they do have different requirements than the code book. That was no fun to find out.

 

[Smart $]

Can I bribe someone into a reply?

Sure...

 

[augie47]

bribe ?? what would you want the answer to say :grin:

Many jurisdictions will accept oversized straps but one hole straps have a habit of "binding" the pipe as they rotate so 2 hole straps are often required. As far as I know, all the PVC manufacturer also have straps designed for their products.

http://www.carlon.com/Product_SupportStrapsClamps.html

 

[Energy-Miser]

use approved straps but contact the manuf. they do have different requirements than the code book. That was no fun to find out.

I tried using the snap on Carlon product. You can see a picture of it on this web site:

http://www.acehardwareoutlet.com/(t4l0kuql1wyo5t45wmrmuq55)/ProductDetails.aspx?SKU=998019024

But true to its name it actually snapped off, while putting in the second screw. It would have been a good choice as it provides a small gap between conduit and the roof surface, as well as allowing longitudinal conduit movement. But it breaks off easily, so I am back to square one.

 

[hardworkingstiff]

use approved straps but contact the manuf. they do have different requirements than the code book. That was no fun to find out.

What requirements are you refering to?

 

[Energy-Miser]

First I would like to point out that there are jurisdictions that do not permit metallic straps, and one is to use PVC straps.

I think the 2-hole straps allow movement for expansion and contraction, and still provide good support of the raceway.

I am using 2-hole pvc straps, but they seem to be a little too small and grab the conduit pretty darn tight.

 

[Energy-Miser]

bribe ?? what would you want the answer to say :grin:

Many jurisdictions will accept oversized straps but one hole straps have a habit of "binding" the pipe as they rotate so 2 hole straps are often required. As far as I know, all the PVC manufacturer also have straps designed for their products.

http://www.carlon.com/Product_SupportStrapsClamps.html

Thanks. I did that, see my post on the use of their snap on straps. E/M

 

[Energy-Miser]

The thing I am hoping for is a 2-hole pvc strap, that is just slightly oversized. But not sure if there is such a thing.

 

[augie47]

I am using 2-hole pvc straps, but they seem to be a little too small and grab the conduit pretty darn tight.

my experience is that the ones designed for PVC do fit tight but allow movement. Local inspectors will accept oversized 2 hole straps but I would check with your AHJ first.

 

[hardworkingstiff]

Around here the AHJ likes to see the strap (you must use the strap designed for PVC) installed with the screw not quite tight.

It's hard to make PVC look good and comply with the expansion/contraction requirments. I like it underground mostly.

 

[LarryFine]

I am using 2-hole pvc straps, but they seem to be a little too small and grab the conduit pretty darn tight.

Same here. I solved that by using straps one size up, especially on rough surfaces. Look at them as staples, not clamps.

You can control the tightness of the strap by varying the spacing of the screws, either farther or closer than straight in.

 

[Energy-Miser]

my experience is that the ones designed for PVC do fit tight but allow movement. Local inspectors will accept oversized 2 hole straps but I would check with your AHJ first.

If the2-hole straps allow for movement then I am ok, because I do like using them. Leaving the screws a little loose however will not work in our application, as the installation is mostly on shingled roofs, and I am afraid a loose screw might encourage leaks.

 

[Energy-Miser]

Same here. I solved that by using straps one size up, especially on rough surfaces. Look at them as staples, not clamps.

You can control the tightness of the strap by varying the spacing of the screws, either farther or closer than straight in.

Yes, I will have to try that.

 

[LarryFine]

... I am afraid a loose screw might encourage leaks.

The strap won't act as a gasket. I suggest a good-sized dab of silicone on the tip of the screw.

 

[iwire]

I am using 2-hole pvc straps, but they seem to be a little too small and grab the conduit pretty darn tight.

Don't drive the screws in so tight ..... seriously.

 

[iwire]

Do not forget the reduced distance between supports for PVC.

 

[LarryFine]

If we need reducing washers, must they be made of PVC, too? :grin: