Gentlemen. We have now stuffed the bridgeport into the back bedroom
and have closed in the giant gaping 8x8' hole in the wall with spiffy
double 36" "french" doors.

This is part of a comprehensive remodeling project. We are converting
the house, a modest 29'x29' 2 bedroom house to an as yet unspecified
commercial purpose.

Some time ago I upgraded the old 100 amp electric service to 200
amps. At that time I moved the service entrance from one end of the
house to the other. Upon removing the old sheet rock from around the
old service entrance I discovered black charring of the insulation
face paper by each one of the romex wires that terminated at the old
box. In other words, the house was just a kiss away from "up in
smoke".

At this point, all of the old wiring throughout the house is dead.
The new service entrance does not connect to any of it. Instead, I
have limited, isolated wiring to two rooms of the house, the front
bedroom and kitchen.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. These boxes do not have
mains. Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.

I have a couple more of these 100 amp boxes. Yesterday I happened to
read the installation instructions in one of these as yet unused
boxes. To my surprise - and discomfiture - I read words to the effect
that "This box is to be used only for branch circuits fed by a box
with not more than 100 amp mains. If fed from a branch breaker this
should be limited to 70 amps."

This is of no immediate concern as these boxes are in temporary
service and are not even close to pulling 50 amps never mind 70 or
100.

Nevertheless, reading this leads me to the presumption that for code?
purposes, branch circuit breakers are not rated as high as main
breakers.

Does anybody know the reason or logic for this?

Gracias. Vernon