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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'>Peter and Larry,<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'>Brian’s post was correct and consistent with the 2011 NEC. It is not correct to apply both 1.25 factors on the dc side. This has been done for years, but it is inconsistent with the rest of the code. Conditions of use are only applied to maximum current—defined by 690.8(A) as rated Isc x 1.25. <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'>It is confusing and that is why the NEC got so specific in the 2011 version.<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 style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>wirewiz@gmail.com<br><b>Sent:</b> Friday, February 11, 2011 12:32 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Calculation of Maximum Circuit Current<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Very good. Thank you Peter.<o:p></o:p></p><div><p class=MsoNormal>On Fri, Feb 11, 2011 at 2:44 PM, Peter Parrish <<a href="mailto:peter.parrish@calsolareng.com" target="_blank">peter.parrish@calsolareng.com</a>> wrote:<o:p></o:p></p><p class=MsoNormal>Short answer: DC/PV side two factors of 1.25; AC side one factor.<br><br>Reasons: the common factor of 1.25 is due to the treatment of PV systems as<br>continuous sources of power, the second factor of 1.25 is for the "cloud<br>effect". It is entirely possible to get more than 1,000 W/m^2 on a PV module<br>if there are large cumulus clouds that don't block the sunlight but act as<br>pretty good reflectors of sunlight.<br><br>As a result you need to increase Isc (times the number of combined strings<br>if that is the case) by 1.56, and all computed AC currents by 1.25. Same<br>goes for and switches and OCPDs.<br><br>Then of course you need to compute the ampacity of the wire being used,<br>taking care to apply the temperature correction and conduit fill correction<br>before comparing to the "maximum current" calculation.<br><br>- Peter<br><br><br>Peter T. Parrish, Ph.D., President<br>California Solar Engineering, Inc.<br>820 Cynthia Ave., Los Angeles, CA 90065<br>CA Lic. 854779, NABCEP Cert. 031806-26<br><span style='color:#888888'><a href="mailto:peter.parrish@calsolareng.com" target="_blank">peter.parrish@calsolareng.com</a><br>Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885</span><o:p></o:p></p><div><p class=MsoNormal><br><br><br>-----Original Message-----<br>From: <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a><br>[mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>] On Behalf Of<o:p></o:p></p></div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'><a href="mailto:wirewiz@gmail.com" target="_blank">wirewiz@gmail.com</a><br>Sent: Friday, February 11, 2011 11:03 AM<br>To: <a href="mailto:RE-wrenches@lists.re-wrenches.org" target="_blank">RE-wrenches@lists.re-wrenches.org</a><br>Subject: [RE-wrenches] Calculation of Maximum Circuit Current<br><br>In studying for NABCEP certification I am a little confused about whether<br>you multiply the short circuit current by 1.25 once or twice (1.56) in order<br>to calculate maximum circuit current in determining wire size. Same for<br>overcurrent protection.<br><br>I have always done it twice (1.56) for both PV source circuit and PV output<br>circuit. Once for over irradiance and once for continuous use.<br><br>But a handout at a recent seminar that I went to totally confused me.<br><br>Can anyone spell it out very clearly?<br><br>Thank you.<br><br>Larry Liesner<br>Wirewiz<br>Westport, CT<br>Phone: 203-644-2404<br>Fax: 203-557-0556<br><a href="mailto:wirewiz@gmail.com" target="_blank">wirewiz@gmail.com</a><br><a href="http://www.wire-wiz.com" target="_blank">www.wire-wiz.com</a><br><br><br><o:p></o:p></p></div></div><div><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" target="_blank">RE-wrenches@lists.re-wrenches.org</a><br><br>Options & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org" target="_blank">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive:<br><a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org" target="_blank">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" target="_blank">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org" target="_blank">www.members.re-wrenches.org</a><br><br><br>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org" target="_blank">RE-wrenches@lists.re-wrenches.org</a><br><br>Options & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org" target="_blank">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" target="_blank">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" target="_blank">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org" target="_blank">www.members.re-wrenches.org</a><o:p></o:p></p></div></div></div><p class=MsoNormal style='margin-bottom:12.0pt'><br><br clear=all><br>-- <br>Larry Liesner<br>System Design<br>Elektron Solar, LLC<br>16 Ketchum St.<br>Westport, CT 06880<br>203-557-3127 (office)<br>203-644-2404 (cell)<br>203-549-0977 (fax)<br><a href="mailto:wirewiz@gmail.com" target="_blank">wirewiz@gmail.com</a><o:p></o:p></p></div></body></html>