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: [email protected] [mailto:[email protected]] 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 _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
