I believe that the breakers from CBI, Midnite and Outback are hydraulic / magnetic and may be operated at 100% While the derating applies to all others that are Thermal / magnetic,
Bob On Fri, Apr 2, 2010 at 11:14 AM, Kent Osterberg <[email protected]> wrote: > Erika, > > You should refer to NEC 690.8 this information. There are two issues that > contribute to the 1.56 factor. First is that the maximum current from the > PV array is considered the short circuit current multiplied by 1.25 to > account for higher than standard irradiance such as cloud edge effect, high > altitude, and high operating temperature. The second multiplier of 1.25 is > because PV current is considered to be continuous. All conductors (and > breakers) operating continuously (over three hours I believe) that are > subject to NEC rules are limited to 80% of the ampacity in Table 310.16. > The two 1.25 factors equals 1.56. > > For normal operation, wires selected under this criteria are conservatively > rated. But it is also the objective of the NEC to design power systems in a > manner that they will remain safe under abnormal circumstances. > > Kent Osterberg > Blue Mountain Solar, Inc. > > > > > Erika M. Weliczko wrote: > > 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 > > > _______________________________________________ > 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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