<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div>I am wondering about the busbar 120% rule, and if there is any wiggle room in the 2014 NEC.</div><div><br></div><div>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?</div><div><br></div><div>Also would you say that the 120% is based on the inverter max output or backfeed breaker size?</div><div><br></div><div><br></div><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>Principal Engineer<br>Heliocentric<br>801-453-9434<br><a href="mailto:taharvey@heliocentric.org">taharvey@heliocentric.org</a><br></span><br><br></div></span>
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