Breaker on #6 copper

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100 foot run in dry condition good up to 65 amp. (ITE ret.) 3 wire conduit size 1"

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Toller wrote:

continuous load. And maybe you might also want to run some lights, a vacuum, a radio, a charger for some handheld tools, etc.?

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M Q wrote:

I should clarify my comments here. The ampacity of the #6 wire depends upon the type of wire. OP didn't say what type. If it is a type that has a 55 A ampacity, then use 50 A breaker. Other types of #6, may have ampacities of 65, 75, or other.
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wrote:

Clarifed or not, your comments are still wrong. It's perfectly OK to use a 60A breaker on a conductor with a listed ampacity of 55A, under Article 240.4(B).
Likewise, if the listed ampacity is 65A, a 70A breaker may be used, and if the listed ampacity is 75A, an 80A breaker may be used -- all because standard breaker sizes do not include 55, 65, or 75 amps.
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Doug Miller (alphageek at milmac dot com)
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wrote:

Wrong. Please familiarize yourself with the NEC before attempting to answer electrical questions.
A 60A breaker is perfectly fine:
"Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met ..." [2005 NEC, Article 240.4(B)]
The conditions can be summarized as not a multiple-receptacle circuit, no matching standard breaker, and next size up not > 800A.

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Doug Miller wrote:

Mea Culpa. I was wrong on two points. Thanks for correcting me.
I will now slink off with my tail between my legs.
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wrote:

You got better treatment than I did from him.
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wrote:

Don't worry about, I have thin skin lately.
But back to my question, which was more out of interest than contesting a ruling. The 5 extra amps is more than just the wire, what about the device at the other end of that wire - it'll be taking on an additional 5 amps too. Maybe not important, if it has its own fuses, they'll blow too. I was just curious is all.
Now this next part is just my mind asking questions, not making personal attacks.
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.
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Eigenvector wrote: <SNIP>

Indeed, electricians are required to know all those fine details.
To get some feel for the breadth of Code issues, look at Mike Holt's pages which include a very busy forum on Code issues: http://www.mikeholt.com/Newsletters/Newsletters.htm
Jim
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Eigenvector wrote: ...

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?categoryID1& 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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dpb wrote:

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--
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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 piss people off, might push them outside their safety zones, might even challenge conventional wisdom, but I'll walk away better educated.
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bud-- wrote:

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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Eigenvector wrote:

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.
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HeyBub wrote: ...

Some of those _may_ have some merit, but I'm doubtful of most...
W/ the NEC, there is a very long and involved process of building the Code and while it isn't required (nor even very meaningful) to publish every nuance of "why" underlying the actual code provisions, there are defensible reasons for them and there has to be sufficient basis to win the approval of a sizable number of participants. At last time I looked there were some 80,000 members of the NFPA and the NEC had something otoh 5,000(!) peer reviewers. With that many folks involved, anything _too_ arbitrary or one-side simply isn't going to fly.
It may appear arbitrary, but like most things, the details are far more complex than they may appear from the outside.
--


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No, actually, they won't. A device draws whatever it draws. A 1200W heater, for example, pulls 10A at 120V whether the circuit it's on has a 15A breaker or a 100A breaker.

Nope; see above.

You don't tell the ampacity just from looking at the wire. Well, you might if you have NEC Table 310.16 memorized, but it's the table that tells you, not the wire.

It should be worrisome if your conclusion were correct; fortunately, it's not.
It's important to remember that the Code allows going up *one*, and only one, breaker size, and then only if the listed ampacity does not correspond to a standard breaker size. For instance, a wire with a listed ampacity of 50A may *not* be breakered at 60A, because 50A is a standard breaker.

There isn't really any difference between the two situations, and the latter is much more convenient to implement in practice.

Perhaps the most important thing that you're missing here is the part of 240.4(B) that says "provided all of the following conditions are met" -- conditions which I only summarized in my earlier posts in this thread. It seems to me that it's time to quote the first one in full, and comment on it:
"(1) The conductors being protected are NOT part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads." [emphasis added]
Let's examine the possibilities under which the bump is permitted by this condition:
1) Circuit has no receptacles at all. That means it's feeding either a subpanel, or direct-wired stationary equipment. In the former case, the load will depend on which circuits in the subpanel are in use, and is unlikely to ever be at maximum. In the latter case, the load is precisely known, and the safety (or lack thereof) is readily determined.
2) Circuit has a single receptacle, or multiple receptacles, for cord-and-plug-connected NON-portable equipment. Again, the actual load can be readily determined: you know what's going to be used on the circuit, because it's sitting right next to the outlets, and it isn't going anywhere. A circuit supplying outlets for a table saw and a 5HP air compressor would be a good example of this category.
3) Circuit has a single receptacle for cord-and-plug-connected portable equipment. It is unlikely that any Code-compliant circuits can exist in this category: the *lowest* listed ampacity that would be permitted to be bumped is a 55A conductor breakered at 60A; it is a Code violation to install a receptacle with a rating lower than that of the overcurrent device on any circuit over 20A; and any load which requires a 60A (or higher) rated receptacle is highly unlikely to meet anyone's definition of "portable".
In short, this means that the bump up to the next higher breaker size is limited to circumstances in which the load is either limited, or more or less fixed, and readily predictable.
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Doug Miller (alphageek at milmac dot com)
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wrote:

Correct; this is specifically permitted under Article 240.4(B).

Remember that the "80% rule" applies only to circuits serving a continuous load, which is defined as "a load where the maximum current is expected to continue for three hours or more." [2005 NEC, Article 100]
This usage probably doesn't meet that definition.

Actually, it applies to both (see Article 210.19(A)(1) [wire] and 210.20(A) [breaker]), but, as noted above, this installation doesn't appear to meet the definition of a continuous load anyway, so it doesn't matter.
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Doug Miller (alphageek at milmac dot com)
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wrote:

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current the entire time.
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Doug Miller (alphageek at milmac dot com)
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