Well the intent is so that no part of the bus bar is exposed to more than its stated rating.  With the inverter breaker at the bottom and the main at the top there isn't any spot on the bus that is subject to the sum of the main and the inverter breaker currents.<div>
<br></div><div>With a center fed panel, the section of the bus bar on the opposite side of the inverter breaker could in fact see the sum of the main and inverter breaker currents.</div><div><br></div><div>I think it is best discussed with the AHJ upfront. <br clear="all">
<div><br></div><div>Brian Mehalic <br>NABCEP Certified Solar PV Installer™ R031508-59<div>IREC ISPQ Certified Affiliated Instructor/PV US-0132<br><div><br></div><div>PV Curriculum Developer and Instructor<div>Solar Energy International<br>
<a href="http://www.solarenergy.org" target="_blank">http://www.solarenergy.org</a></div></div></div></div><br>
<br><br><div class="gmail_quote">On Mon, Oct 15, 2012 at 12:32 PM, August Goers <span dir="ltr"><<a href="mailto:august@luminalt.com" target="_blank">august@luminalt.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi Wrenches,</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Here is yet another 120% rule question as it relates to center fed main panels. 2011 NEC 705.12 deals with inverter point of connection and 705.12(D)(7) reads:</span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">"</span><b><span style>Inverter Output Connection.</span></b><span><span style> </span></span><span style>Unless the panelboard is rated not less than the sum of the ampere ratings of all overcurrent devices supplying it, a connection in a panelboard shall be positioned at the opposite (load) end from the input feeder location or main circuit location."</span></p>

<p class="MsoNormal"><span style> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">We are seeing more and more center fed main panels where the main breaker is in the middle of the busbars and there are branch circuit breakers located both above and below the main breaker. The question is whether it is possible to meet the intent of the code if the main breaker is rated the same as the panel. Here is a picture to illustrate:</span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><a href="https://docs.google.com/open?id=0BxRKBvO2EOGudU5KSUJnYnFRYnc" target="_blank">https://docs.google.com/open?id=0BxRKBvO2EOGudU5KSUJnYnFRYnc</a></span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">In this example, is it okay to install our inverter breaker on either the bottom or the top? If not, then our only resort is to either upgrade the service or downsize the main breaker which isn't always possible to do.</span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Thanks for your thoughts in advance.</span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Best,</span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">August</span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">August Goers</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Luminalt Energy Corporation</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">m: <a href="tel:415.559.1525" value="+14155591525" target="_blank">415.559.1525</a></span></p>

<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">o: <a href="tel:415.641.4000" value="+14156414000" target="_blank">415.641.4000</a></span></p><p class="MsoNormal">
<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><a href="mailto:august@luminalt.com" target="_blank">august@luminalt.com</a></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>

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