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#41
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Breaker on #6 copper
"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. |
#42
Posted to alt.home.repair
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Breaker on #6 copper
bud-- wrote:
dpb wrote: .... Having served on another Standards committee subcommittee in the past with similar rules, it is a protracted process to say the least... Which one? .... Ages ago now...an IEEE subcommittee pondering details of error evaluation and measurement for instrumentation for nuclear plant applications... I think that particular Standard has been superseded long since -- but the process remains similar for most standards-writing bodies. As I recall that one subcommittee drug on for over three years alone before the final approval process was completed. -- |
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