1. You need to know the actual rating of any sub-section buss that you
will be backfeeding with PV. Do not backfeed this buss with more than
100% of it's ampacity.
2. Evaluate 120% of the 4000A buss against the 3500A main and all PV
backfeed all of the subsections.
Mark Frye
On 2/17/2015
Mark,
Thank you, your response is very helpful! How does the 120% rule get
applied to the 1000A sections in my example? When grid connecting
downstream on the load side of the switches on the 1000A sections do we ignore
the rating of the 1000A bus bar being protected by a 3500 Amp Fuse?
NEC 2008, 240.21 (B)(1)(1) a.
Each of the smaller buss sections are feeders which are sized according
to the tap rules. I believe the answer to your question is that the
larger fuse can't protect the smaller buss. *But*, the likelihood of a
short developing in that section of the circuit is
Wrenchers,
I run into lots of Service Equipment that has a Large Service Switch which
feeds multiple Sections with the Bus bar on each section rated significantly
less than the main bus.A specific example that I am currently looking at
has a 4000Amp Switch with a 3500 Amp Fuse which feeds 3
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