Re: [RE-wrenches] sizing a sub-panel used to combine multiple inverter outputs

[Kent Osterberg]

Per 705.12(D) the sub-panel could be any distribution equipment on the premises. So the question becomes: is the sub-panel capable of supplying branch circuits or feeder loads? If yes, then the sum of the breakers (potentially) feeding the bus is 180 amps so a 150-amp rating is required and the inverters would have to feed the opposite end of the bus bars. If no, the code is not clear on the requirement, but obviously the 80-amp breaker in the main panel limits the maximum current flowing through the sub-panel. Kent Osterberg Blue Mountain Solar Al Frishman wrote: Hi Wrenchers, When using a sub-panel for the sole purpose of combining the output of multiple single phase inverters does NEC 690.64 (B) (2) apply?  I know that this topic has been discussed but I am still not clear.   The “Can we Land” Article pg 11 Diagram 2b shows that using a Subpanel eliminates the problem of exceeding the 120% rule illustrated in diagram 2a but it does not show the rating of the sub-panel.    In the example it shows 3 Fronius 7500W single phase inverters landing in a sub-panel and then the 3-phase sub-panel grid connected to a 80A 3-phase breaker in a 400A main panel.    What is the minimum Amp rating required for the 3-phase Sub-panel in diagram 2b?  Do we only need to size it for the OCP for the combined outputs of the 3 inverters (80A) or do the three 50A two-pole breakers need to be considered?   For easy reference here is a link to the article: http://www.spgsolar.com/wp-content/uploads/2010/05/SPGLeBlancYates.pdf   All feedback is appreciated.   Al Frishman AeonSolar (917) 699-6641 - cell (888) 460-2867 www.aeonsolar.com     _______________________________________________ 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

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