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<TITLE>Re: [RE-wrenches] sizing a sub-panel used to combine multiple inverter outputs</TITLE>
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<FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>Agreed:<BR>
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<a href="http://solarprofessional.com/article/?file=SP2_3_pg16_QandA_2&search=">http://solarprofessional.com/article/?file=SP2_3_pg16_QandA_2&search=</a><BR>
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You’ll notice that none of the more permissive proposals that John mentions here actually made it into NEC 2011.<BR>
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On 3/30/11 1:07 PM, "Jason Szumlanski" <<a href="Jason@fafcosolar.com">Jason@fafcosolar.com</a>> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'><FONT COLOR="#1F497D">Here is a 690.64(B)(2) opinion from Wiles that may help. <BR>
<a href="http://www.fafcosolar.com/download/409/690%2064%28B%29%282%29TECH-1.pdf">http://www.fafcosolar.com/download/409/690%2064%28B%29%282%29TECH-1.pdf</a><BR>
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It’s still my contention that the conductors need to be sized for 150A in this example, unless an exception is made by the AHJ. If David Brearley’s post about Wiles’ clarification is accurate, them the 80A main breaker in the subpanel can be used for calculations, but the conductor still needs to be sized for 80A + 80A =160A / 1.2 = 133.3A.<BR>
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</SPAN></FONT><FONT COLOR="#1F497D"><FONT FACE="Cambria"><SPAN STYLE='font-size:12pt'>Jason<BR>
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</SPAN></FONT><FONT SIZE="2"><FONT FACE="Tahoma, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:10pt'><B>From:</B> <a href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <B>On Behalf Of </B>Kent Osterberg<BR>
<B>Sent:</B> Wednesday, March 30, 2011 12:57 PM<BR>
<B>To:</B> RE-wrenches<BR>
<B>Subject:</B> Re: [RE-wrenches] sizing a sub-panel used to combine multiple inverter outputs<BR>
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Al,<BR>
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How about a 15-amp single-pole breaker for power line carrier communications equipment to talk to the inverters?<BR>
Technically, I think either way they are loads and that changes everything. But in my opinion they are minor and should be allowed without considering the sum of all sources.<BR>
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Kent Osterberg<BR>
Blue Mountain Solar<BR>
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Al Frishman wrote: <BR>
</SPAN></FONT><FONT COLOR="#1F497D"><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>Is a monitoring system installed in the Load Center to measure the cumulative kWh’s of the inverter’s considered a load? <BR>
The type of monitoring device I am talking about has CT’s that go around the conductors and the Voltage ref is taken by attaching conductors to each phase, the Neutral and the ground bar. The digital Meter has a 3-pole 5A breaker in it so the conductors in the load center can be connected to lugs on the bus bar directly.<BR>
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</SPAN></FONT></FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'><BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Helvetica, Verdana, Arial"><SPAN STYLE='font-size:10pt'><I>Al Frishman<BR>
</I></SPAN></FONT></FONT><FONT COLOR="#030100"><FONT SIZE="4"><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:13pt'>Aeon</SPAN></FONT></FONT></FONT><FONT SIZE="4"><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:13pt'><FONT COLOR="#FF9700">Solar<BR>
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</SPAN></FONT><FONT SIZE="2"><FONT FACE="Tahoma, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:10pt'><B>From:</B> <a href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <B>On Behalf Of </B>Jason Szumlanski<BR>
<B>Sent:</B> Wednesday, March 30, 2011 8:18 AM<BR>
<B>To:</B> RE-wrenches<BR>
<B>Subject:</B> Re: [RE-wrenches] sizing a sub-panel used to combinemultipleinverter outputs<BR>
</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT COLOR="#1F497D"><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>Another key is to remember that this discussion also applies to the conductor between the main panel and subpanel. In a large PV system, this could result in a pretty large wire between the two panels, and a significant cost that is often overlooked. In some cases it makes sense to locate the subpanel close to the main panel and run multiple sets of smaller wires from the inverters to the subpanel.<BR>
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And because the calculation is based on the first OC protection connected to the inverters, adding a main breaker (theoretically 80A in this example) in the subpanel doesn’t change things. Even though this wire would be theoretically protected by an 80A breaker at each end, you can’t size the wire for 160A / 1.2 = 133.3A. You have to size for 180A/1.2 = 150A. (not that it makes much of a difference in this example, but it still must be considered)<BR>
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At least that’s how I understand it…<BR>
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</SPAN></FONT></FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'><BR>
</SPAN><FONT COLOR="#1F497D"><SPAN STYLE='font-size:12pt'>Jason Szumlanski<BR>
</SPAN><SPAN STYLE='font-size:11pt'>Fafco Solar</SPAN><FONT SIZE="1"><SPAN STYLE='font-size:4pt'> <BR>
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</SPAN></FONT><FONT SIZE="2"><FONT FACE="Tahoma, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:10pt'><B>From:</B> <a href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <B>On Behalf Of </B>Mark Frye<BR>
<B>Sent:</B> Wednesday, March 30, 2011 1:33 AM<BR>
<B>To:</B> 'RE-wrenches'<BR>
<B>Subject:</B> Re: [RE-wrenches] sizing a sub-panel used to combinemultipleinverter outputs<BR>
</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT COLOR="#0000FF"><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Opps!<BR>
</SPAN></FONT></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT COLOR="#0000FF"><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>My bad, I was thinking of a single phase system, not the three phase system shown in the article.<BR>
</SPAN></FONT></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT COLOR="#0000FF"><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>For the three phase system Kent is correct in counting 180A of supply per bar.<BR>
</SPAN></FONT></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Mark Frye</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Berkeley Solar Electric Systems</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>303 Redbud Way</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Nevada City, CA 95959</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>(530) 401-8024</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>www.berkeleysolar.com</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <<a href="http://www.berkeleysolar.com/">http://www.berkeleysolar.com/</a>> </SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'> </SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
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</SPAN></FONT><FONT SIZE="2"><FONT FACE="Tahoma, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:10pt'><B>From:</B> <a href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <B>On Behalf Of </B>Mark Frye<BR>
<B>Sent:</B> Tuesday, March 29, 2011 10:17 PM<BR>
<B>To:</B> 'RE-wrenches'<BR>
<B>Subject:</B> Re: [RE-wrenches] sizing a sub-panel used to combine multipleinverter outputs<BR>
</SPAN></FONT><SPAN STYLE='font-size:10pt'><FONT COLOR="#0000FF"><FONT FACE="Arial">I think Kent and I agree. For the case where the subpanel is not dedicated a PV sub-panel he is calculating for 2 - 50A breakers and I calculated for 3 - 50A breakers.<BR>
</FONT></FONT></SPAN></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'><BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Mark Frye</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Berkeley Solar Electric Systems</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>303 Redbud Way</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>Nevada City, CA 95959</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>(530) 401-8024</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'>www.berkeleysolar.com</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <<a href="http://www.berkeleysolar.com/">http://www.berkeleysolar.com/</a>> </SPAN></FONT><FONT SIZE="2"><FONT FACE="Arial"><SPAN STYLE='font-size:10pt'> </SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
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</SPAN></FONT><FONT SIZE="2"><FONT FACE="Tahoma, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:10pt'><B>From:</B> <a href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <B>On Behalf Of </B>Kent Osterberg<BR>
<B>Sent:</B> Tuesday, March 29, 2011 9:26 PM<BR>
<B>To:</B> RE-wrenches<BR>
<B>Subject:</B> Re: [RE-wrenches] sizing a sub-panel used to combine multiple inverter outputs<BR>
</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'>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. <BR>
<BR>
Kent Osterberg<BR>
Blue Mountain Solar<BR>
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</SPAN></FONT></FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>David Brearley, Senior Technical Editor<BR>
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