There is a good Technical Note on the SMA website that talks about sizing an AC combining panel that may provide some guidance on this.
http://download.sma.de/smaprosa/dateien/4307/Multiple%20SB%20Installation%20 on%203%20Phase%20Utility%20Tech%20Note%20V21.pdf -Glenn Burt From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Palumbo Sent: Tuesday, October 12, 2010 12:15 AM To: 'RE-wrenches' Subject: Re: [RE-wrenches] Supply side connection to a dedicated panel We are installing a 8kW grid tied PV system for a commercial client. There is an auto start generator on the premises, therefore we will be utilizing a supply side AC point of connection. Inverter is an SMA SB8000. System owner plans on adding to system in the next few years. We are designing for a total of 24kW of PV. We will install a 200A fused disconnect off the grid feed (line side of the generator transfer switch). My plan is install a dedicated breaker panel for the inverter 240VAC output(s). The SB8000 is rated at 29 Amps, so a 40A DP breaker will do for the point of connection. This panel will eventually have a total of (3) 40A DP breakers each with 8kW of inverter output. My question has to do with the interpretation of the 120 percent rule of the rating of the busbar in the panel. Do I need to use a 225 Amp rated panel with a downsized 150A main breaker? 225A busbar x 1.2 = 270 Amps -150A MB = 120A total of inverter output allowed. Or, since this panel will only be used for inverter AC point of connection, and not for loads, is it allowable to label this panel as a "Dedicated Panel - connect no loads". If that is the case we could use a 200A panel, or even a 150Amp panel. A local electrician proposed this "dedicated panel" to avoid the larger load center panel. I cannot find any mention of "dedicated panel" in the NEC. I think what I am proposing follows 690.64. Any opinions, or advice would be appreciated. Dave Palumbo Independent Power LLC www.independentpowerllc.com NABCEP Certified PV Installer Vermont Solar Partner 802.888.7194
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