Mark,
Although this exception is allowed, I think it is bad practice in the field. We will probably see the NEC revoke this exception within the next few cycles, and it may be revoked for PV systems much sooner. Relying on box connections to carry the low fault currents inherent in PV systems is a really bad idea. The NEC is a minimum standard. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Mark Frye Sent: Friday, October 09, 2009 3:42 PM To: 'RE-wrenches' Subject: Re: [RE-wrenches] Rooftop wiring methods between multiple subarrays Hey Folks, I don't want to dicourage anyone from doing good work that meets or exceeds Code requirements. But I am a little quizzical about the how we all seem to be ignoring what the Code actual says about this. "250.97 Bonding for Over 250V Volts.... Exception: Where oversized, concentric, or eccentric knockouts are not encountered....the following methods shall be permitted:...(3) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors..." This tells me that if I run PV source conductors in EMT from one metal box to another, I don't nessecarily need to bond the EMT as if it were part of a service. Mark Frye Berkeley Solar Electric Systems 303 Redbud Way Nevada City, CA 95959 (530) 401-8024 <http://www.berkeleysolar.com/> www.berkeleysolar.com _____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of August Goers Sent: Friday, October 09, 2009 12:57 PM To: RE-wrenches Subject: Re: [RE-wrenches] Rooftop wiring methods between multiple subarrays All - PVC doesn't hold up well in the Bay Area - Here's a photo of some ~4 year old PVC browned PVC from Marin County: PVC (Small).jpg You can see that the straps melted resulting in the conduit sliding down. Thank goodness we didn't install this. PCV seems like a good option for shaded areas. As Bill pointed out, if we use EMT we need to bond both ends of the conduit to comply with NEC 250.97. My issue is that it is hard to find outdoor rated bonding bushings - that's why we've just been installing cast metal boxes with threaded connections (complies with NEC 250.92(B)(2)). As William point out, EMT is robust and reliable. I still think that there must be more efficient way to go between arrays. Maybe that's why commercial low profile racking systems are often fully integrated systems with built in wire raceways. -August August Goers Luminalt Energy Corporation O: 415.564.7652 M: 415.559.1525 F: 650.244.9167 aug...@luminalt.com From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Friday, October 09, 2009 12:07 PM To: RE-wrenches Subject: Re: [RE-wrenches] Rooftop wiring methods between multiple subarrays Ray: Good question. We do use PVC in coastal zones to avoid corrosion. We try to keep it in the shade, paint it where exposed to UV and support it in close intervals. William At 10:57 AM 10/9/2009, you wrote: Except for coastal installations.... where EMT is NOT recommended outdoors, PVC browns out and warps, and we should therefore use product X??? R. Walters r...@solarray.com Solar Engineer On Oct 9, 2009, at 11:38 AM, William Miller wrote: August: I suggest the use of EMT with proper fittings to protect high voltage, high amperage DC Wiring on rooftops. Sure it is time consuming, but high quality, reliable craftsmanship will always be thus. William Miller
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