<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Troy,</div><div>This is my first post. </div><div>We install 32 amp rated output inverters, reduce the main breaker to 175amp, or line side tap. <br><br><div>Phil Forest</div><div>South Mountain Company</div></div><div><br>On Apr 2, 2014, at 1:40 PM, Troy Harvey <<a href="mailto:taharvey@heliocentric.org">taharvey@heliocentric.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=windows-1252">Thanks Bill, Makes sense to me too. Splitting your current over two sections of busbar, as calculated by P=I^2R, does seem like it will in reality reduce the heat load in the load center.<div><br></div><div>However, no good AHJ solutions today. We are finding the most customers have been moving towards larger systems as panel prices have fallen. If typical service is 200AMP, and that average american household usage is ~32kWh/day, that is approx. a 8kW system in most areas. And 8kW inverter * 125% means a 43AMP backfeed. Next size up is 50amp. That is bigger than 120%. This is most every project we work on these days is over 120%. </div><div><br></div><div>So how is everyone else dealing with this?<div><br><div apple-content-edited="true">
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-variant: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span style="font-size: 11px; ">thanks,<br><br>Troy Harvey<br><br></span><br><br></div></span>
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<br><div><div>On Mar 28, 2014, at 8:38 PM, Bill Brooks <<a href="mailto:billbrooks7@yahoo.com">billbrooks7@yahoo.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class="WordSection1" style="page: WordSection1;"><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Dave and Troy,<o:p></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">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></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Devil’s advocates state that people violate Article 220 all the time so we need to be conservative.<o:p></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Make a proposal at the meeting in Golden on April 9-10 and you may become famous.<o:p></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Bill.<o:p></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div><div style="border-style: solid none none; border-top-color: rgb(225, 225, 225); border-top-width: 1pt; padding: 3pt 0in 0in;"><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><b><span style="font-size: 11pt; font-family: Calibri, sans-serif;">From:</span></b><span style="font-size: 11pt; font-family: Calibri, sans-serif;"><span class="Apple-converted-space"> </span><a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" style="color: purple; text-decoration: underline;">re-wrenches-bounces@lists.re-wrenches.org</a><span class="Apple-converted-space"> </span>[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" style="color: purple; text-decoration: underline;">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]<span class="Apple-converted-space"> </span><b>On Behalf Of<span class="Apple-converted-space"> </span></b>Troy Harvey<br><b>Sent:</b><span class="Apple-converted-space"> </span>Friday, March 28, 2014 1:35 PM<br><b>To:</b><span class="Apple-converted-space"> </span>RE-wrenches<br><b>Subject:</b><span class="Apple-converted-space"> </span>Re: [RE-wrenches] Busbar 120% rule<o:p></o:p></span></div></div></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">Very interesting. <o:p></o:p></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">So, it is not a overcurrent risk, but a heat issue that<span class="Apple-converted-space"> </span><i>may</i><span class="Apple-converted-space"> </span>lead to a nuisance breaker tripping issue?<o:p></o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div><div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">On Mar 27, 2014, at 12:46 PM, Dave Click <<a href="mailto:daveclick@fsec.ucf.edu" style="color: purple; text-decoration: underline;">daveclick@fsec.ucf.edu</a>> wrote:<o:p></o:p></div></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><br><br><o:p></o:p></div><blockquote style="margin-top: 5pt; margin-bottom: 5pt;"><div><p class="MsoNormal" style="margin: 0in 0in 12pt; font-size: 12pt; font-family: 'Times New Roman', serif;">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" style="color: purple; text-decoration: underline;">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<span class="Apple-converted-space"> </span><br>safe for restricted conductors, it may not be suitable for busbars in panel boards, even<span class="Apple-converted-space"> </span><br>though this allowance is in the 2008 NEC. Panel boards are subject to busbar current<span class="Apple-converted-space"> </span><br>limitations and are also subject to thermal limitations due to the heating associated with<span class="Apple-converted-space"> </span><br>the thermal trip elements in the common thermal/magnetic molded case circuit breakers.<span class="Apple-converted-space"> </span><br>For example a 100-amp, 120/240V panel board is tested during the listing process with a<span class="Apple-converted-space"> </span><br>100 amp main breaker and two 100-amp load breakers (one per phase) mounted directly<span class="Apple-converted-space"> </span><br>below the main breaker. The ambient temperature is raised to 45 degrees Celsius, the<span class="Apple-converted-space"> </span><br>input and output currents are set at 100 amps, the temperature is allowed to stabilize,<span class="Apple-converted-space"> </span><br>and the panel must pass this test with no deformation of any parts. If we add a backfed<span class="Apple-converted-space"> </span><br>PV breaker pair, for example 50 amps, at the bottom of the panel, and if the loads on the<span class="Apple-converted-space"> </span><br>panel were increased to 150 amps, no breakers would trip, no busbars would be over<span class="Apple-converted-space"> </span><br>loaded, but the thermal load in the panel would be that associated with 300 amps, not the<span class="Apple-converted-space"> </span><br>200 amps the panel was designed and listed for. Panel manufacturers have stated that<span class="Apple-converted-space"> </span><br>these panels cannot pass UL listing tests with those excessive thermal loads.</i><o:p></o:p></p><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">On 2014/3/27, 14:34, Troy Harvey wrote:<o:p></o:p></div></div><blockquote style="margin-top: 5pt; margin-bottom: 5pt;"><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">I am wondering about the busbar 120% rule, and if there is any wiggle room in the 2014 NEC.<o:p></o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">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></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">Also would you say that the 120% is based on the inverter max output or backfeed breaker size?<o:p></o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><p class="MsoNormal" style="margin: 0in 0in 12pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><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" style="color: purple; text-decoration: underline;">taharvey@heliocentric.org</a><br><br></span><o:p></o:p></p></div><div style="margin: 0in 0in 0.0001pt; 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