Allen,
The benefit I see would be to allow for a code compliant load side connection on a 200A panel with a 200A MB, where the AHJ is on the 2008 NEC or older and will not listen to your good logic. I don't think this would always be the best option, but if backup loads and inverter output were less than 32A then a 40A OCPD in the main panel should be fine? Since it sounds like the 60A breaker in the main panel is not a safety issue, but a design consideration, I suppose I would just prefer flexibility when possible. That said, this AHJ is on the 2008, and the loads will be less than 30A, but based on this conversation I plan to go with a 60A and try to convince the AHJ that it will be code compliant in their future! Thanks, Garrison From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Allan Sindelar Sent: Thursday, February 28, 2013 8:14 AM To: RE-wrenches Subject: Re: [RE-wrenches] Conductor Sizing for Supply Side Connection Garrison, I don't know why it's not listed as 60A max, but my own internal logic would ask why it should be. The only benefit I could see for using smaller than a 60A breaker would be to allow use of #8 conductors (allowed with a 40A or 50A breaker) instead of the #6 necessary with a 60A breaker. And of course, you could use a 40A breaker with #6 conductors, so theoretically it would be fine. I just fail to see any benefit to doing so. Allan Allan Sindelar <mailto:al...@positiveenergysolar.com> al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc. 3209 Richards Lane (note new address) Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com <http://www.positiveenergysolar.com/> On 2/28/2013 6:27 AM, Garrison Riegel wrote: Thanks Allen for clarifying why a 60A is required. I was wondering. The spec does list a surge current of 9000W so I thought that may be the rationale, but even that would only require a 50A, and since this surge occurs during 'stand-alone mode' it didn't seem to apply to the OCPD at the main panel. Your explanation makes more sense, but I wonder why then they don't list the AC input breaker size as 60A max. If you have few backup loads, and are not on the 2011 NEC, a 40A could theoretically be fine? Thanks all for your thoughts, much appreciated. Garrison From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Allan Sindelar Sent: Wednesday, February 27, 2013 6:08 PM To: RE-wrenches Subject: Re: [RE-wrenches] Conductor Sizing for Supply Side Connection August, The 60A breaker is intended to allow grid power to pass through to the loads in excess of the inverter's stand-alone output. The point of 705.12 (moved in the 2011 NEC from 690.64 (B)(2)) is to differentiate between load pass-through current and sell current. The amount of current fed into the grid is (4500/230 =) 19.56A, while the amount that can be taken from the grid and passed through to the load is much greater. If you were limited to a 40A breaker in order to maintain 120% of a 200A main bus, you'd be prone to nuisance trips under large cumulative loads. Allan Allan Sindelar <mailto:al...@positiveenergysolar.com> al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc. 3209 Richards Lane (note new address) Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com <http://www.positiveenergysolar.com/> _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address & 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
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