If you back feed at the end of the bus bar where the main is connected
to the middle of the bus bar, the back fed breaker cannot overload the
bus bar between the main and the back fed breaker, but it would be
possible to overload the other side of the bus bar - it's being fed by
both the main and the back fed breaker. Seems like you shouldn't apply
the 120% rule to these panels. But realistically, the panel isn't likely
to be overloaded because most 200-amp panels are fed by services that
can't really deliver 200 amps, at least not for more than a very brief time.
And what about the SQ D QO or HOM 6-12L100 or 8-16L100 panels that can
be fed with main lugs that are on opposite ends (left for L1 and right
for L2)? Seems like you shouldn't apply the 120% rule to these either.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
On 10/15/2012 9:32 AM, August Goers wrote:
Hi Wrenches,
Here is yet another 120% rule question as it relates to center fed
main panels. 2011 NEC 705.12 deals with inverter point of connection
and 705.12(D)(7) reads:
"*Inverter Output Connection.*Unless the panelboard is rated not less
than the sum of the ampere ratings of all overcurrent devices
supplying it, a connection in a panelboard shall be positioned at the
opposite (load) end from the input feeder location or main circuit
location."
We are seeing more and more center fed main panels where the main
breaker is in the middle of the busbars and there are branch circuit
breakers located both above and below the main breaker. The question
is whether it is possible to meet the intent of the code if the main
breaker is rated the same as the panel. Here is a picture to illustrate:
https://docs.google.com/open?id=0BxRKBvO2EOGudU5KSUJnYnFRYnc
In this example, is it okay to install our inverter breaker on either
the bottom or the top? If not, then our only resort is to either
upgrade the service or downsize the main breaker which isn't always
possible to do.
Thanks for your thoughts in advance.
Best,
August
August Goers
Luminalt Energy Corporation
m: 415.559.1525
o: 415.641.4000
aug...@luminalt.com <mailto:aug...@luminalt.com>
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