[RE-wrenches] Supply side connection to a dedicated panel

[Glenn Burt]

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-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at 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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