To add to Brian's well formulated response, the 2011 NEC is much more detailed and accurate on this subject. Oversizing wire is not a big deal on residential systems, but it is prohibitively expensive in megawatt jobs.
Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Brian Mehalic Sent: Friday, February 11, 2011 11:19 AM To: RE-wrenches Subject: Re: [RE-wrenches] Calculation of Maximum Circuit Current Maximum current is defined in 690.8(A) as Isc x 1.25. Minimum OCPD size is defined in 690.8(B) as maximum current x 1.25 (Isc x 1.56). The maximum size, for PV source circuits, is the module maximum series fuse size. Required conductor ampacity is the greater of Isc x 1.56 or Isc x 1.25 with all conditions of use factors (and the conductor must be protected by the OCPD under conditions of use). Brian On Fri, Feb 11, 2011 at 11:03 AM, <wire...@gmail.com> wrote: In studying for NABCEP certification I am a little confused about whether you multiply the short circuit current by 1.25 once or twice (1.56) in order to calculate maximum circuit current in determining wire size. Same for overcurrent protection. I have always done it twice (1.56) for both PV source circuit and PV output circuit. Once for over irradiance and once for continuous use. But a handout at a recent seminar that I went to totally confused me. Can anyone spell it out very clearly? Thank you. Larry Liesner Wirewiz Westport, CT Phone: 203-644-2404 Fax: 203-557-0556 wire...@gmail.com www.wire-wiz.com _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org -- ======================== Brian Mehalic NABCEP Certified Solar PV InstallerT PV Online Coordinator Solar Energy International Carbondale, CO 81623 http://www.solarenergy.org
_______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
