Hans, The 2002 NEC 352.12D states that RNMC can't be used where ambient temps exceed 50C unless listed otherwise. Most of the PVC we see is listed otherwise, max 90C right on the conduit.
Jeff -----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 6:33 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: ________________________________ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Max Balchowsky Sent: Monday, August 24, 2009 2:28 PM To: RE-wrenches Subject: Re: [RE-wrenches] raintite box mounting angle We use a high voltage coating to water proof splices, whether they be wire nuts (which I don't like to use on DC circuits) or the plastic coated terminal strips, which I prefer. That's left over from my days as a traffic signal technician and splicing loop detectors in below grade pull boxes, which, more often than not, fill with water in the rain. Joel, I used the metal boxes (with the weep hole ) in the desert, but here on the coast the plastic boxes seem to work fine, and I've had some installs that are 10 years old (back to the beginning of the ladwp program). What I saw to be a problem in the heat was the jobs I was called in to fix (other contractor's installs) where they used the plastic PVC conduit on the roof - always came loose in the heat. It's designed for underground, not surface work. Max Balchowsky SEE Systems 760-403-6810 ________________________________ From: Joel Davidson <joel.david...@sbcglobal.net> To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Sent: Monday, August 24, 2009 1:25:36 PM Subject: Re: [RE-wrenches] raintite box mounting angle I always drill a 3/16-inch weep hole in boxes that could fill up with water. Even properly vertically mounted boxes can get water in them. In Sacramento, I had some metal conduit homerun from the roof and then down a 25 ft north wall. The conduit was like condensing tubes that dripped water into the DC disconnect boxes at the bottom of the vertical conduit runs. Joel Davidson ________________________________ From: Peter Parrish <peter.parr...@calsolareng.com> To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Sent: Monday, August 24, 2009 1:11:49 PM Subject: [RE-wrenches] raintite box mounting angle Max, A cautionary tale. We used those puppies for a while until we had a call back from a customer with a ground fault / off line condition. We found that the box had warped, the seal rendered ineffective and the splices sitting in 0. 5" of water. After thinking about it, we decided that the 140+ deg F summer roof temperatures probably caused the plastic to warp under thermal stress. They probably would work just fine off the roof, but I can't personally vouch for them. - Peter Peter T. Parrish, Ph.D., President California Solar Engineering, Inc. 820 Cynthia Ave., Los Angeles, CA 90065 CA Lic. 854779, NABCEP Cert. 031806-26 peter.parr...@calsolareng.com Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 ________________________________ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Max Balchowsky Sent: Monday, August 24, 2009 12:48 PM To: RE-wrenches Subject: Re: [RE-wrenches] raintite box mounting angle We've been using the 6x6x4 plastic boxes with a gasket (electrical section of most home depot stores)- mount them on their side at the edge of the array. They are rated for electrical wiring and are water proof and have been accepted and passed by every electrical inspector we've had over the last few years. They are used alot by landscape contractors for j-boxes in the ground. Max Balchowsky SEE Systems 760-403-6810 ________________________________ From: Bill Brooks <billbroo...@yahoo.com> To: k...@vtsolar.com; RE-wrenches <re-wrenches@lists.re-wrenches.org> Sent: Monday, August 24, 2009 9:08:34 AM Subject: Re: [RE-wrenches] raintite box mounting angle Kirk, I'm fairly confident that if the manufacturer does not specify an angle for NEMA 3R (rainproof) that the default is vertical. In special cases (e.g. Outback PSPV), the NEMA 3R tests are requested at an angle, but this is fairly rare. Upshot is that NEMA 3R boxes normally cannot be mounted in the plane of the roof, while NEMA 4 and up can be mounted in the roof plane since many of these boxes can be mounted from vertical to horizontal. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Kirk Herander, VSE Sent: Monday, August 24, 2009 8:26 AM To: 'RE-wrenches' Subject: [RE-wrenches] raintite box mounting angle Hello, Can anyone give a recommendation for a minimum mounting angle of a raintite box? Ideally 90 degrees, but in this case I may be forced to mount it at the same angle as the panels - about 25 degrees, mounted off the roof about 6 inches. I don't think there is any reference in the NEC to this. It will be off the roof about 6 inches in a mild climate, where they only get about 20 inches of snow a year. Thanks. Kirk Herander Vermont Solar Engineering 802.863.1202 NABCEP(tm) Certified Solar Installer NYSERDA-eligible Installer VT Solar Incentive Program Partner _______________________________________________ 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 _______________________________________________ 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
