In article , ignoramus21810
@NOSPAM.21810.invalid says...
Now, a killer question. How come the breakers on the panel do not
qualify as overcurrent protection devices under NEC. They are, after
all, designed to interrupt the line if the current exceeds the rated
amount. The whole issue of just how much current can be supplied to
the panel, is depending on the answer to this question.


It's a good question. I went through this a year ago when
building a large industrial control panel. Usually when I
do this sort of thing it's for a self contained piece of
automation I've built, so this issue does not come up
because the connections to the various devices are not
"premises wiring" and do not constitute a branch circuit.
In the case in question there were many pumps and fans
powered by the panel spread around a large room, with their
wiring mingled with the plant wiring.

Even though you can buy a suitable CB for your home panel
for a few dollars, and the miniature circuit breakers
(MCBs) referenced in the article below are reasonably
priced, the breakers approved for branch circuit protection
and suitable for use in an industrial control enclosure
start around $200/ea for a 3 phase device, and are
physically very large. We ended up protecting the
conductors leaving the cabinet with Class CC fuses, which
are approved for the use. By the time you buy the fuses and
a quality finger safe holder, they're more expensive than
the MCBs.

Here's a link to MCBs...
http://www.eatonelectrical.com/NASApp/cs/ContentServer?
pagename=C-H/Common/AssetTemplateLink&c=Apubarticles&cid=
987090561951&Sec=products

and the big molded case breakers...
http://www.eatonelectrical.com/NASApp/cs/ContentServer?
pagename=C-H/Common/AssetTemplateLink&c=Apubarticles&cid=
1063683114821&Sec=products

This article is a pretty good summary of the issue. If you
want to google up more the key words are "supplementary
protection", UL 489, and UL 1077.

http://www.ce-mag.com/archive/02/Spring/deionno.html

Ned Simmons