Slipped pinky finger sent my post a bit early. Sorry... Here's the Carlon document for PVC expansion fittings: http://www.carlon.com/Installation_Training/IT-ISEXPJT.pdf
My feeling is that in general, how thermal expansion/contraction issues are handled is one of the most important factors in the longevity of solar PV installations. Not just for conduit, but for racking and module construction as well. If I recall correctly, an expansion coupling (or lack thereof) was the cause of the Staples fire. -Hans -----Original Message----- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Hans Frederickson Sent: Monday, August 24, 2009 3:33 PM To: 'RE-wrenches' Subject: [RE-wrenches] Thermal issues with PVC (was RE: raintite boxmounting angle) Picking up on Max's comment about PVC conduit coming apart in the heat... PVC is acceptable for use above ground, but is often not a good choice in exposed outdoor areas due to thermal issues: First, PVC conduit is not permitted to be used where ambient temperatures exceed 50 degrees C (122 degrees F) per NEC 352.12(D). This limitation rules out using PVC on most roofs, although you will occasionally see it used on "cool" roofs in our neck of the woods (pacific NW). It follows that PVC junction boxes would not typically be a good idea on a hot roof unless they are specifically listed for higher temperatures. Second, PVC of any significant length installed outdoors generally will require an expansion fitting. See NEC 352.44 for details. The rule of thumb we use around here is any piece of PVC conduit longer than 10' installed on an exterior wall needs an expansion fitting. If you find yourself needing to install an expansion fitting, this document from Carlon is very helpful: _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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
