"bud--" wrote in message
...
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--
Well I certainly appreciate the clarification guys. Not attempting to
ruffle feathers here, certainly not attempting to flame out the newsgroup.
But when I hear something that doesn't make sense to me I ask, its what I do
most of the day at the office so it's natural back home. Besides, what I've
learned is that asking questions is the best way to understand and correct
deficiencies, it might **** people off, might push them outside their safety
zones, might even challenge conventional wisdom, but I'll walk away better
educated.