Dana:
I assume from your description that the top buss is lug fed. One would
need to know the value of overcurrent protection feeding those lugs to
perform the calculations.
Take the rating of a given buss (or feeder) and multiply by 120%. Subtract
from the result the value of the breaker feeding that buss (or feeder) and
you have the maximum breaker size you can backfeed on that buss (or to that
feeder),
William Miller
PS: The breakers labelled Main are not main disconnects. They are load
breakers. The split buss satisfies the "six throws" rule.
Wm
At 05:19 PM 10/28/2010, you wrote:
Hi everyone,
I'm working on two systems for homes that have the old style breaker
panels with no single main breaker. Instead, they have six breakers in the
upper part of the panel each labeled "main breaker," which satisfies the
six disconnect rule. The bus bar is split, with one of the six upper
breakers (60A) feeding a separate bus in the lower half of the panel. It
appears that the upper bus is rated for 200A, and the lower at 100A. The
sum of the main breakers does not exceed the 200A rating of the upper bus.
There are spare breaker slots on both the top and bottom buses. How do I
deal with 690.64 (B) (2) when there's no main breaker?
Thanks!
Dana
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