[RE-wrenches] Expansion on conduits on commercial roof tops!

[Hans Frederickson]

We've covered this a few times before. Here's a recap of my previous
comments:

1) I use EMT on rooftops, not PVC. PVC conduit just moves too much to be
safe for a lot of expansion/contraction long-term. However, if you're in
Hawaii, you might have a different set of issues. EMT could rust out quickly
and perhaps your temperature swings aren't as great.

2) If you do decide to go with steel conduit, it moves much less than PVC,
and you can get a longer run in before you need an expansion coupling. To
calculate expansion, see the FPN for NEC 300.7(B). You take the values in
Table 352.44 and multiply by 0.2 for steel conduit.

3) Pay attention to how you strap your conduit. The straps adjacent to an
expansion coupling need to be loose enough to allow the conduit to slip as
it expands/contracts.

4) OZ-Gedney makes a UL-listed expansion coupling for EMT, the TX series.

Regards,
-Hans


From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of James
Rudolph
Sent: Thursday, December 22, 2011 6:39 AM
To: RE-wrenches
Subject: [RE-wrenches] Expansion on conduits on commercial roof tops!

Howdy Wrenches,

I was wondering how everybody is dealing with expanding conduits on roof
tops? Do we have an accepted best practice on this?. What I am really
looking for is a way to starp long conduit runs on commercial rooftops in
direct sun that allow movement and expanision joints to do thier job.

Mahalo in advance!



James B Rudolph
NABCEP Certified PV Installer