[RE-wrenches] Supply Side Interconnections - Maximum Backfeed

Kirpal Khalsa solarworks at gmail.com
Thu Mar 4 13:16:59 PST 2010


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 <mike at solarflair.com> 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
> mike at solarflair.com
>
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