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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Eric,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><br>Your reasoning sounds logical, but it is missing the point. Transformers have to be protected by overcurrent devices, similar to wire. Inverters are current limited devices so they only have to be able to withstand a certain size circuit breaker. The current from the inverter is considered continuous so most circuit breakers are designed to operate at 80% of their rating continuously (therefore the requirement to multiply inverter output current by 125%).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Does that make any more sense?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Bill.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Bill Brooks, PE<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Principal<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Brooks Engineering<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>3949 Joslin Lane<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Vacaville, CA 95688<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>707-332-0761 (office and mobile)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>bill@brooksolar.com (email)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>www.brooksolar.com (web)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><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 [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>eric@harvesthesun.com<br><b>Sent:</b> Monday, October 31, 2016 3:34 PM<br><b>To:</b> RE-wrenches <re-wrenches@lists.re-wrenches.org><br><b>Subject:</b> [RE-wrenches] Undercurrent Protection?<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>I realize this is potentially a stupid question, and one that is long overdue, but here goes:<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>Why in 690(B) are we setting a minimum threshold on OCPD when we're protecting <u>against</u> over current?<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>Shouldn't we be setting a maximum threshold...as is done in pretty much all other cases? The way I see it, we should take the array/inverter max output AC current and multiply by 125% to set our min ampacity on <u>wire</u>,<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>and then calc down to find the breaker trade size that lands between the max AC output current and max AC output current times 125%. That way, we avoid nuisance tripping but achieve the max overcurrent protection possible.<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>By following 690(B) we're actually decreasing OCP: Literally, 690(B) is stating that we can have a breaker 100x over the circuit rating, so long as it's not under the circuit rating times 1.25. To me this seems antilogical.<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>Mr. Brooks?<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>690.9(B) Overcurrent Device Ratings. Overcurrent device ratings<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><u><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>shall be not less than 125 percent</span></u><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> of the maximum<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>currents calculated in 690.8(A).<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>455.7(B)...The overcurrent protection determined<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>from this section <u>shall not exceed 125 percent</u> of the<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>phase converter nameplate single-phase input amperes.<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>450.4(A)...Such overcurrent device<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>shall be rated or set at <u>not more than 125 percent</u> of<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>the rated full-load input current of the autotransformer.<o:p></o:p></span></p></div></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>450.5(A)(2) Overcurrent Protection. An overcurrent sensing device<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>shall be provided that will cause the main switch or commontrip<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>overcurrent protection referred to in 450.5(A)(1) to open if<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>the load on the autotransformer <u>reaches or exceeds 125 percent</u><o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>of its continuous current per-phase or neutral rating.<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'> <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>450.5(B)(2)(b) Ampere Rating. The overcurrent protection shall be<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>rated or set at a current <u>not exceeding 125 percent</u> of the <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>autotransformer continuous per-phase current rating or<o:p></o:p></span></p></div><div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>42 percent of the continuous-current rating of any seriesconnected<o:p></o:p></span></p></div><div><p class=MsoNormal style='background:white'><span style='font-size:18.0pt;font-family:"Garamond",serif;color:#222222'>devices in the autotransformer neutral connection.<o:p></o:p></span></p></div></div></div></div></div><div><p class=MsoNormal> <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><p class=MsoNormal>Eric Stikes<o:p></o:p></p></div><div><p class=MsoNormal>Founding Director & CEO<o:p></o:p></p></div><div><p class=MsoNormal>Good Sun Solar, A CA non-profit corp.<o:p></o:p></p></div><div><p class=MsoNormal><a href="http://www.goodsun.life">www.goodsun.life</a><o:p></o:p></p></div><div><p class=MsoNormal>(530) 559-5023<o:p></o:p></p></div></div></body></html>