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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>I understand what you are saying about the 40A breaker, but according to 690.64(B)(2), “…with panelboards connected in series, the rating of the <b>*first*</b> overcurrent device connected <b>*directly*</b> to the output of the inverters shall be used in the calculations for <b>*all*</b> busbars and conductors.” The way I have seen that interpreted is that the main distribution panel needs to be rated to support 120% of the two inverter circuits plus the main breaker, regardless of the fact that there is a 40A backfeed breaker in the main panel.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>200+30+15 > 200 x 1.2<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I know it doesn’t make much sense, but that’s the way it’s been interpreted around here. It stands to reason that this applies only to the PV subpanel busbar and the conductors between the panels, and that the calculation for those should be:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(30 + 15 + 40) / 1.2 = 70.83A required ampacity<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>…and the calculation for the main distribution panel should be:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(200 + 40) / 1.2 = 200A required ampacity<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>… but that’s not what I am being told.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='font-size:12.0pt;color:#1F497D'>Jason Szumlanski<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Fafco Solar<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p></div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Mark Frye<br><b>Sent:</b> Thursday, September 29, 2011 4:19 PM<br><b>To:</b> 'RE-wrenches'<br><b>Subject:</b> Re: [RE-wrenches] Adding on to existing PV System<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:blue'>Jason:</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:blue'>SB 5000 = 21A @ 240V, 21A x 1.25 = 26.3A needs 30A breaker</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:blue'>M215 = 0.9 A @ 240V, 0.9A x 9 = 8.1 A, 8.1 x 1.25 = 10.1A needs 15A breaker. (Or that rounded to 10A and use a 10A breaker)?</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:blue'>26.3A + 10.1A = 36.4 A needs 40A breaker</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:blue'>So, get a new 100A main lug subpanel. Connect it to a 40A breaker in the existing main panel. Move the existing 30A breaker into the new subpanel and install the new 15A breaker into the same.</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><br></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Mark Frye</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <br></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Berkeley Solar Electric Systems</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <br></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>303 Redbud Way</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <br></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Nevada City, CA 95959</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <br></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>(530) 401-8024</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <br><a href="http://www.berkeleysolar.com/"><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>www.berkeleysolar.com</span></a></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'> </span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <o:p></o:p></span></p><div><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'> <o:p></o:p></span></p></div><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p><div class=MsoNormal align=center style='text-align:center'><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><hr size=2 width="100%" align=center></span></div><p class=MsoNormal style='margin-bottom:12.0pt'><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Jason Szumlanski<br><b>Sent:</b> Thursday, September 29, 2011 12:55 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Adding on to existing PV System</span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>That’s not a bad idea, except that 690.64(B)(2) requires that the breaker directly connected to each inverter(s) must be used for the calculation.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I have an existing SB5000 with a 30A breaker and a new string of nine Enphase M215’s requiring a 15A breaker. If you combine these in a 100A or higher rated subpanel with a 40A main breaker, you still calculate the total current supplying the busbar in the main distribution panel based on 200A + 30A + 15A = 245A (with 30A and 15A being the overcurrent protection directly connected to the inverters). This exceeds the 120% rule by 5A. It also requires that the ampacity of the conductors between the two panels be 85A / 1.2 = 70.83A (assuming a 40A backfeed breaker in the main distribution panel). If your interpretation is different, please let me know!<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>If my interpretation is correct, I like the idea of just adding a fusible disconnect and using #10 conductors all the way to the tap. That would be the most cost effective solution I believe, and since there is no foreseeable further system rating increases, the advantage of a subpanel is reduced.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Thanks for all the other suggestions provided. Unfortunately I can’t put in smaller main breaker, and the busbar in the main panel is definitely rated 200A.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='font-size:12.0pt;color:#1F497D'>Jason Szumlanski<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Fafco Solar<o:p></o:p></span></p></div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Glenn Burt<br><b>Sent:</b> Thursday, September 29, 2011 2:40 PM<br><b>To:</b> 'RE-wrenches'<br><b>Subject:</b> Re: [RE-wrenches] Adding on to existing PV System<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#1F497D'>How about feeding both systems into an AC combining subpanel before feeding the main load center?<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Often the calculations required will allow you to do more backfeeding than the simple backfeeding a load center with individual breakers.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>-Glenn<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Jason Szumlanski<br><b>Sent:</b> Thursday, September 29, 2011 11:49 AM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> [RE-wrenches] Adding on to existing PV System<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>We’ve been contracted to add on to an existing PV system in a residence. The existing system has a 30A 2P Breaker on a 200A rated panel with a 200A main breaker. The new system would require a 15A breaker, which would exceed the limit in NEC 690.64(B)(2).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The existing system has a fusible AC disconnect mounted next to the meter. This was originally intended as the utility external disconnect. The utility no longer requires a disconnect, but if we do a supply side connection, we would need a fusible AC disconnect anyway for the new system. I would collocate the new disconnect with the old.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Does anyone see any problem with doing a supply size connection for the new system? Any labeling snags that I might need to consider?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-size:12.0pt'>Jason Szumlanski<o:p></o:p></span></p><p class=MsoNormal>Fafco Solar<o:p></o:p></p></div></body></html>