Erika you are correct, the solar radiance can exceed STC by about 125%, any one who has spent any time with a pyrometer has observed this. From experience's continuously operated circuits fail fasted than intermittent circuits. for the temperature and conduit fill, they are valid of course, but solar are not overcurrent protected, it is possible to have a solar circuit be shorted and stay sorted for months or even a year. If this happens it is still hoped that the system will not cause a fire.
Darryl --- On Fri, 4/2/10, Bill Brooks <[email protected]> wrote: From: Bill Brooks <[email protected]> Subject: Re: [RE-wrenches] DC wire sizing To: [email protected], "'RE-wrenches'" <[email protected]> Date: Friday, April 2, 2010, 11:14 AM Erika, The most correct answer (which is a really funny thing to say) is to use John Wiles’ “5-step program”—that’s what I call it. It is published in one of the appendices of his latest “Suggested Practices” document. If you can actually follow what he leads you through (that’s why I call it the 5-Step program), it will lead you to the correct answer. My short answer, that can result in a larger than necessary conductor, is to determine the required overcurrent protection device (OCPD) rating and then size the conductor accordingly. The reason it may be conservative is that the NEC allows you to round to the next larger standard OCPD in 240.4(B). This is the way all conductors are sized in the electrical industry. I’m all about simplicity and being a little conservative is always better than being overly liberal (I’m not making a political statement here, but if the shoe fits…). Bill. From: [email protected] [mailto:[email protected]] On Behalf Of Erika M. Weliczko Sent: Friday, April 02, 2010 6:27 AM To: 'RE-wrenches' Subject: [RE-wrenches] DC wire sizing To my understanding the 156% on PV source and output circuits is related to the ability of PV to deliver more than rated and be continuous. Therefore, the wire has to be able to carry this current, so now the temperature and fill corrections are applied to find the wire capable of the 156%. I am in a debate where the question is why correct for temp and fill on 156% of ISC and spend all that extra money when the normal operating is at Imp. Or why correct the 156% but why not correct the Isc or Imp. I am going to stick to the fact that the circuit has to carry the 156% under all conditions… Thoughts? Erika -----Inline Attachment Follows----- _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] 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
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