Eigenvector wrote:
....
A lot of people are firing back claiming the wire can handle 65 A, 60 A,
2000A, whatever, those current carrying capacities aren't advertised on the
wire bundle, so how would an electrician know that? I'm presuming an
electrician isn't schooled at the same level as an Electrical Engineer. So
looking at a wire and being able to tell the ampacity of it seems liberal to
me. 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.

The electrician doesn't have to know what the theoretical
current-carrying capacity of a conductor is -- all he has to do is learn
the basic rules of NEC (or whatever particular code variant he is
working under).

The NEC is a product of the NFPA which is a nonprofit organization
formed initially by a bunch of insurance underwriters for the purpose of
trying to bring some order into common practice and to reduce the
prevelance/frequency of fires owing to poor practice (and, given the
time in which they started, not in small part, to define what good
practice entailed.)

The code is pragmatic and not intended as a technical treatise or
engineering specification. That saic, there are bases for each rule and
reasons for the rule and the exceptions to the rules. As others have
said, the tendency is to make the rules conservative with respect to
actual practices that would be an imminent and immediate danger.

Code is written by committee of member representatives and is, for the
most part, a volunteer activity. For an overview of the Code
development process, see the following link...

http://www.nfpa.org/categoryList.asp?categoryID=161&
URL=Codes%20and%20Standards/Code%20development%20process

Having served on another Standards committee subcommittee in the past
with similar rules, it is a protracted process to say the least...

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