Vernon wrote:


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?
Yup, interrupting rating. If you examine the breakers closely (may
require a magnifying glass) it will probably have a lable saying
something like "interrupting rating 10,000 A" or maybe "branch circuit
must not exceed 10,000 A surge capacity". This relates to the current
surge during a severe short circuit event. The breaker MUST be able to
interrupt the worst-case surge without exploding. Downstream branches
are protected by the current limiting effect of upstream breakers.
The main panel breakers in our building are huge things, and carry a 100
KA rating, the rest of the breakers have a 10KA rating.

Jon