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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='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dave and Troy,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I don’t think JW had his facts correct on this. The standard test for a busbar is to place the highest allowable breakers directly below the main breaker to test for overtemperature of the busbar. With the requirement for Article 220 compliance of the panel, a panel that actually complies with Article 220 could go to 200% and will likely run cooler than a panel only fed by the utility. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Devil’s advocates state that people violate Article 220 all the time so we need to be conservative.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Make a proposal at the meeting in Golden on April 9-10 and you may become famous.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Bill.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Troy Harvey<br><b>Sent:</b> Friday, March 28, 2014 1:35 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Busbar 120% rule<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Very interesting. <o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>So, it is not a overcurrent risk, but a heat issue that <i>may</i> lead to a nuisance breaker tripping issue?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>On Mar 27, 2014, at 12:46 PM, Dave Click <<a href="mailto:daveclick@fsec.ucf.edu">daveclick@fsec.ucf.edu</a>> wrote:<o:p></o:p></p></div><p class=MsoNormal><br><br><o:p></o:p></p><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><p class=MsoNormal style='margin-bottom:12.0pt'>I had a nice response all typed up before rediscovering my original source. Simple answer: there's still a thermal load to deal with even though there's no point on the bus seeing a current above the busbar rating. I am a linking machine today:<br><a href="http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/690.64(B)(2)Load%20Side%20Connections.pdf">http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/690.64(B)(2)Load%20Side%20Connections.pdf</a><br><br><i>While this situation of connecting supply overcurrent devices at opposite ends may be <br>safe for restricted conductors, it may not be suitable for busbars in panel boards, even <br>though this allowance is in the 2008 NEC. Panel boards are subject to busbar current <br>limitations and are also subject to thermal limitations due to the heating associated with <br>the thermal trip elements in the common thermal/magnetic molded case circuit breakers. <br>For example a 100-amp, 120/240V panel board is tested during the listing process with a <br>100 amp main breaker and two 100-amp load breakers (one per phase) mounted directly <br>below the main breaker. The ambient temperature is raised to 45 degrees Celsius, the <br>input and output currents are set at 100 amps, the temperature is allowed to stabilize, <br>and the panel must pass this test with no deformation of any parts. If we add a backfed <br>PV breaker pair, for example 50 amps, at the bottom of the panel, and if the loads on the <br>panel were increased to 150 amps, no breakers would trip, no busbars would be over <br>loaded, but the thermal load in the panel would be that associated with 300 amps, not the <br>200 amps the panel was designed and listed for. Panel manufacturers have stated that <br>these panels cannot pass UL listing tests with those excessive thermal loads.</i><o:p></o:p></p><div><p class=MsoNormal>On 2014/3/27, 14:34, Troy Harvey wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><p class=MsoNormal>I am wondering about the busbar 120% rule, and if there is any wiggle room in the 2014 NEC.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Fundamentally I don't understand the 120% rule. If my solar breaker is installed properly at the bottom of the busbar, and the grid-tie breaker is installed at the top, and the busbar itself is rated for 120% of the panel rating, I don't see any means by which a solar breaker of a size substantially larger than 120% could cause a problem. There can be no place on the busbar under any situation (that I can think of) that would exceed 120% because the supply current is coming from opposite ends of the bus bar - even in the worst case load situation. So even if I had a huge PV system (100A), backfeeding the bottom of a 200A panel, I don't see a situation where there is more than 200A over any one section of busbar. Am I wrong, or is the NEC just too prescriptive for its own good?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Also would you say that the 120% is based on the inverter max output or backfeed breaker size?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:8.5pt'>thanks,<br><br>Troy Harvey<br>---------------------<br>Principal Engineer<br>Heliocentric<br>801-453-9434<br><a href="mailto:taharvey@heliocentric.org">taharvey@heliocentric.org</a><br><br></span><o:p></o:p></p></div></div><p class=MsoNormal><br><br><br><br><o:p></o:p></p><pre>_______________________________________________<o:p></o:p></pre><pre>List sponsored by Home Power magazine<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Change email address & settings:<o:p></o:p></pre><pre><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List-Archive: <a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List rules & etiquette:<o:p></o:p></pre><pre><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Check out participant bios:<o:p></o:p></pre><pre><a href="http://www.members.re-wrenches.org/">www.members.re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre></blockquote><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><br><br>Change email address & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive: <a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a><br><br>List rules & etiquette:<br><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org">www.members.re-wrenches.org</a><o:p></o:p></p></blockquote></div><p class=MsoNormal><o:p> </o:p></p></div></div>
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