dpb wrote:
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...


Which one?


Nice description, I quite generally agree.
IIRC the chemical industries forced a change from "hazardous" wiring to
"classified" wiring. And I think the health care industries forced more
significant changes to the chapter on health care facilities. Both
examples quite old but there are probably still 'aberrations'. The
process in general works pretty well.


A few of the steps for NEC revision:

Proposed changes are submitted by anyone.

A panel makes decisions on the proposals and the results are published
in the "Report on proposals" - ROC.

The public makes comments on the proposed changes.

The panel makes decisions using the comments and the results are
published in the "Report on comments" -- ROC.

There are a few more steps.



The ROP and ROC are available (when I last looked) on the internet.
Reading them can be interesting. You get the logic for the change (and
occasionally lack of logic). When a proposed change fails you may get
the logic (or lack of logic) for why the code is written as it is.

--
bud--