Eigenvector wrote:
When they allow higher breaker
sizes it also tells me that the NEC conventions are largely anecdotal
or arbitrary as opposed to calculated or theoretical values - which
is even more worrisome to me. I would expect them to state
restrictions and rules more along the lines of "This is the
theoretical limit of this particular wire, plus a safety margin of
1.5 - you may not use something higher than this value" Rather than,
"Just use the next highest one, they don't make the correct one for
it." If they were to state something like that, I would also expect
them to qualify it by stating the reason why they make that
allowance. Like I said, just me asking questions.

Like most "regulations," there is no requirement that a "reason" be given.
Often the regulation is arbitrary and based on emotional satisfaction rather
than science (silicone breast implants, arsenic levels in municipal water
systems).

Other times, like having a licensed electrician (or union member), be
responsible for changing a light bulb, the underlying reason is political or
economic.

Sometimes, like the regulations prohibiting PEX in California, the
regulation is merely a pride issue.