Going all the way up to the rating of the service might not be such a good idea. The utility may use smaller wires for the service drop than you would expect based on the ampacity tables in the NEC. Considering the example of a 400 A service:
- PG&E (local utility) requires 350 kcmil Aluminum conductors. - Table 310.17 rates 350 kcmil Aluminum for 395 amps before temperature correction. With load diversity the smaller wires will be fine, but the output of a PV system is continuous. Running the output of a system sized at 400 amps through the wires on a hot summer day could overload them. So... it depends. Scott Scott McCalmont, P.E. McCalmont Engineering San Jose, CA (408) 204-0318 On Thu, Mar 4, 2010 at 3:02 PM, Michael Kelly <[email protected]> wrote: > Kirpal, > > That was always my interpretation as well. So in the case of a 400A > service, I can backfeed 400A when utilizing a supply side connection. > Others have thoughts on this? > > - Mike > > -- > Michael Kelly > Project Manager / Project Engineer > NABCEP Certified Solar PV Installer ™ > > SolarFlair Energy, Inc. > 11 Mayhew Street > Framingham, MA 01702 > Direct Mobile: 617-899-9840 > Main Phone: 508-293-4293 > Main Fax: 508-293-4003 > [email protected] > > > On Thu, Mar 4, 2010 at 4:16 PM, Kirpal Khalsa <[email protected]>wrote: > >> Mike.....i may be wrong....but I think i am right....you are limited by >> the wire size feeding the supply and/or the transformer size which supplies >> the service.....depending on the physical location of the tap you may be >> limited by the enclosure and the enclosure ratings as well >> would love to hear any other ideas... >> Cheers, >> -- >> Sunny Regards, >> Kirpal Khalsa >> >> NABCEP Certified Solar PV Installer >> Renewable Energy Systems >> www.oregonsolarworks.com >> 541-218-0201 m >> 541-592-3958 o >> >> >> On Thu, Mar 4, 2010 at 12:50 PM, Michael Kelly <[email protected]>wrote: >> >>> Hi All, >>> >>> Next to grounding, I find the calculation of the maximum amount of >>> backfeed current allowed in a supply side connection to be the most vague >>> issue in Article 690. Let's assume we have a 400A, 480/277 service in a >>> commercial building, a 400A main service disconnect, and the jurisdiction is >>> under NEC 2008. What is the maximum backfeed current allowed in a supply >>> side connection? The only place the code points you to is 230.82(6), which >>> is no help, or to Article 705, which is no help either. I know that in the >>> draft version of NEC 2011, there is an expansion of 705.12(A) which states " >>> * *Supply Side. An electric power production source shall be permitted >>> to be connected to the supply side of the service disconnecting means as >>> permitted in 230.82(6). The sum of the ratings of all overcurrent devices >>> connected to power production sources shall not exceed the rating of the >>> service." That is a helpful sentence from the Code, but as it is in draft >>> form, what do we do under NEC 2008? What have you used as a maximum >>> backfeed current for supply side connections? >>> >>> Thanks, >>> Mike >>> -- >>> Michael Kelly >>> Project Manager / Project Engineer >>> NABCEP Certified Solar PV Installer ™ >>> >>> SolarFlair Energy, Inc. >>> 11 Mayhew Street >>> Framingham, MA 01702 >>> Direct Mobile: 617-899-9840 >>> Main Phone: 508-293-4293 >>> Main Fax: 508-293-4003 >>> [email protected] >>> >>> _______________________________________________ >>> 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 >>> >>> >>> >> >> >> _______________________________________________ >> 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 >> >> >> > > _______________________________________________ > 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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