[RE-wrenches] Supply Side Interconnections - Maximum Backfeed

Michael Kelly mike at solarflair.com
Thu Mar 4 12:50:07 PST 2010


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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