<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:12pt"><div><span>I have found inspectors agree that if it is labled "Solar only no Load circuits" the main breaker protects this panel, or the sum of the breakers does not exceed the busbar rating, the panel is protected without using the 120% rule</span></div><div><span>I agree with Kirk </span></div><div><br></div> <div style="font-family: arial, helvetica, sans-serif; font-size: 12pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <font size="2" face="Arial"> <div style="margin: 5px 0px; padding: 0px; border: 1px solid rgb(204, 204, 204); height: 0px; line-height: 0; font-size: 0px;" class="hr" contentEditable="false" readonly="true"></div> <b><span style="font-weight: bold;">From:</span></b> Kirk Herander <kirk@vtsolar.com><br> <b><span style="font-weight:
bold;">To:</span></b> 'RE-wrenches' <re-wrenches@lists.re-wrenches.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Tuesday, June 26, 2012 3:53 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> [RE-wrenches] combiners and the 120% rule<br> </font> </div> <br>
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--></style><div><div class="yiv983380671WordSection1"><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">Jason,</span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);"> </span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">In your email below you state:</span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);"> </span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">“</span>You DO need to observe the 120% rule for the combining subpanel, regardless of whether there are loads present, at least in jurisdictions where I have worked. I've heard that some inspectors will allow you to ignore it if it is labeled as a PV combiner with "add no loads" notation.<span style="color: rgb(31, 73, 125);">”</span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">
</span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">NEC 705.12 (D) states that the distribution equipment (in this case the combiner panel, fed by multiple inverters and a utility source) must be “capable of supplying multiple branch circuits or feeders or both” for (D)(1) through (7) to apply. If you fully populated a combiner panel with inverter breakers, leaving no slots for load breakers, it is not capable of supplying branch circuits or feeders, and IMO the 120% rule does not apply to the combiner buss or the conductors back to its point of utility interconnect. I have argued this point as well as label combiners “load circuits prohibited” (with or without available slots) and received AHJ approval.</span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);"> </span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">You could also just lock
shut a combiner that had spare slots as a deterrent to adding load breakers.</span></div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);"> </span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'> </span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>Kirk Herander</span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>VT Solar, LLC</span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>dba Vermont Solar Engineering</span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>NABCEP<sup>TM </sup>Certified installer Charter Member</span></div><div
class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>NYSERDA-eligible Installer</span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>VT RE Incentive Program Partner</span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'>802.863.1202</span><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 18pt;'></span></div><div class="yiv983380671MsoNormal"><span style='color: rgb(31, 73, 125); font-family: "sans-serif"; font-size: 14pt;'> </span></div><div class="yiv983380671MsoNormal"><b><span style='font-family: "sans-serif"; font-size: 10pt;'>From:</span></b><span style='font-family: "sans-serif"; font-size: 10pt;'> 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> Tuesday, June 26, 2012 8:28 AM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Enphase grid tie question</span></div><div class="yiv983380671MsoNormal"> </div><div class="yiv983380671MsoNormal">I'll email you off-list a 1-line diagram from a system with 164 microinverters broken down into 8 strings in a 208V system. This particular system used two subpanels to accumulate PV, but that was only because we had to backfeed two existing subpanels due to the size of existing 480/208V transformers. You will have to look at the utility service and all existing equipment.</div><div><div class="yiv983380671MsoNormal"> </div></div><div><div class="yiv983380671MsoNormal">Regarding the breakers in the subpanel, you will only need a maximum of a 20A breaker for each string. The max inverters per string is 25 and the calculation for OCPD is:</div></div><div><div class="yiv983380671MsoNormal">
</div></div><div><div class="yiv983380671MsoNormal">215W / 208V x 25 inverters / 1.732 x 1.25 = 18.65A</div></div><div><div class="yiv983380671MsoNormal"> </div></div><div><div class="yiv983380671MsoNormal"><span style="color: rgb(31, 73, 125);">“</span>You DO need to observe the 120% rule for the combining subpanel, regardless of whether there are loads present, at least in jurisdictions where I have worked. I've heard that some inspectors will allow you to ignore it if it is labeled as a PV combiner with "add no loads" notation.<span style="color: rgb(31, 73, 125);">”</span></div></div><div><div class="yiv983380671MsoNormal"> </div></div><div><div class="yiv983380671MsoNormal">Use a MLO panel with a fusible disconnect between the subpanel and the interconnection point. If you use a 225A panel, you can feed it with 270A. With eight 20A backfed PV circuits, you would need to protect the line side of the panel with a 100A fusible
disconnect. That probably isn't going to work. You may be best off from a cost perspective using two 225A subpanels and two 60A fusible disconnects. Anything larger than a 60A 3P disconnect and the price skyrockets. It all depends on your circuit calculations and the existing equipment. Of course, you would need two spaces for your interconnection point.</div></div><div><div><div><div class="yiv983380671MsoNormal"> </div></div><div><div class="yiv983380671MsoNormal">Jason Szumlanski</div><div><div class="yiv983380671MsoNormal">Fafco Solar</div></div></div></div><div style="margin-bottom: 12pt;" class="yiv983380671MsoNormal"> </div></div></div></div></div><br>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org" ymailto="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><br><br>Options & settings:<br><a
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