Going to the next higher overcurrent divice

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finhead

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If thirty-five 14 AWG TW current carrying conductors are installed in a raceway, the applicable adjustment factor of 0.4 would limit the ampacity of the conductors to 8 amps.
Assuming the building where this occurs employs circuit breakers for overcurrent protection, would the next higher overcurrent device be 15 (the next higher circuit breaker) or 10,the next higher standard fuse size?
Any help would be appreciated.
Brian Dolan
 
Re: Going to the next higher overcurrent divice

I'm interested to see other peoples interpretations here. I guess I had never really thought of the question in this way.

The way I read 240.4(B) is that you can chose either a standard circuit breaker size or a standard fuse size. Therefore, you could use a 15 amp circuit breaker, or a 10 amp fuse.

The kicker here is that your load must be limited to 8 amps. If you are wiring a bunch of receptacles, there would be no way to do that and I would consider it a violation. If you are feeding a fixed load, I don't see a problem with it.
 
Re: Going to the next higher overcurrent divice

If I were to take the words of 240.4(B) literally, I would say that you must use the next higher standard overcurrent device rating, or one that has an even lower rating. If the ampacity is 8, the next higher device rating is 10. That tells me you must use a 10 amp fuse or a fuse rated no higher than 8 amps, and that you cannot use a 15 amp breaker.

Reading again in a purely literal manner, I infer that you can use an 8 amp breaker, if you can find one. But you cannot use a 10 amp breaker, even if you can find one.
 
Re: Going to the next higher overcurrent divice

Brian,
It doesn't matter if the 14s are serving multiple receptacle outlets, because in that case you can't use the next larger size.
The code is silent on your question, but it would be common sense that you could go to a 15 amp breaker if you have a breaker panel or a 10 amp fuse if you have a fuse panel.
The other issue is that the load on these conductors would have to be 8 amps or less.
Don
 
Re: Going to the next higher overcurrent divice

Actually, if the loads are continuous they would have to be less than 6.4 amps.

Per 210.3 the smallest rating for a general use branch circuit is 15A.

240.6(A) allows the use of non-standard ampere ratings like 10A breakers.
 
Re: Going to the next higher overcurrent divice

Originally posted by jim dungar: Per 210.3 the smallest rating for a general use branch circuit is 15A.
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But the question did not say this was for general use branch circuits. So that constraint does not apply.
Originally posted by jim dungar: 240.6(A) allows the use of non-standard ampere ratings like 10A breakers.
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True. But it is not 240.6(A) that allows us to use an overcurrent device that is rated higher than the ampacity of the conductor. What allows that is 240.4(B), and it requires that we use the next higher standard device. That is the basis of my earlier statements. You can use an 8 amp breaker because that would be lower than the ampacity. You cannot use a 10 amp breaker, even though you might be able to use a 15 amp breaker, because the 15 is a standard size, and the 10 is not.

I half wondered if anyone would challenge that assertion. ;)
 
Re: Going to the next higher overcurrent divice

Charlie, my 210.3 comment was in regards to the "receptacles" mentioned by previous posters.

I did not say that 240.6(A) allows you to use a larger rating, only that CB ratings smaller than 15A are allowed.

There is nothing in 240.4 that says you must use the next standard rating, it only says the next standard rating shall be permitted. This terminology does not prevent you from using a non-standard rated device that is lower than a standard rating.
 
Re: Going to the next higher overcurrent divice

Originally posted by jim dungar: There is nothing in 240.4 that says you must use the next standard rating, it only says the next standard rating shall be permitted. This terminology does not prevent you from using a non-standard rated device that is lower than a standard rating.
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240.4 says you must protect conductors at their ampacity, unless allowed otherwise by (A) through (G). 240.4(B) allows you to go to the next higher standard rating. But it does not say you can go to a non-standard rating that exceeds the ampacity.

In other words, with an ampacity of 8, you can use a standard 10 amp fuse, but not a non-standard 9 amp fuse. It might seem pointless, but I am addressing the words, as written. 240.4(B) does not give us the lattitude to make any selection we wish. We don't get to pick and choose amongst that which lies in the middle ground. We can use 240.4(B) as written, else we must revert to 240.4.
 
Re: Going to the next higher overcurrent divice

finhead
What application is this for?
If it happens to be for a class 1 non power limited motor control...then the derating rules don't apply unless the conductors have more than 10% of rated ampacity.
 
Re: Going to the next higher overcurrent divice

Charlie, what specific words prevent the AHJ from allowing the use of a larger non-standard device that does not exceed the next largest standard rating?

According to the NEC style manual. "Shall be permitted ... indicate allowed optional or alternate methods. (Note that these are still mandatory language and constitute rules.) The term may shall only be used where it recognizes a discretionary judgment on the part of an authority having jurisdiction."
 
Re: Going to the next higher overcurrent divice

The reason I raised the question because of a book published by EC&M magizine called "Understanding NE Code Rules on Motors and Motor Controls". One chapter delt with more than one motor on one branch circuit. Assuming a 3-phase system using circuit breakers, several motors are shoen installed on one 15 or 20 amp circuit. This only works if the next higher OCPD is a circuit breaker. Acording to the this book, the rule was changed in the 1965 NEC to permit this arrangement.
Brian Dolan
 
Re: Going to the next higher overcurrent divice

Originally posted by jim dungar: Charlie, what specific words prevent the AHJ from allowing the use of a larger non-standard device that does not exceed the next largest standard rating?
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When a rule says "you shall do this," and it is followed by another rule (or an exception) that says "you shall be permitted to do this instead," it does not give you free reign to do anything that you might like. You can do the second thing, but if you choose not to then you must do the first thing. You cannot do anything else.

In this case, it would be far better to protect the 8 amp conductors with an 8 amp fuse. But the code authors did not want to force us to buy non-standard fuses. So they allowed us to use a higher size, simply because the size we need is not a standard size.
 
Re: Going to the next higher overcurrent divice

Charlie, I agree that the code authors did not want to force us to buy a non-standard device. My point is I do not see the language prohibiting the AHJ from permitting the use of a lower non-standard rating.
 
Re: Going to the next higher overcurrent divice

Originally posted by jim dungar: My point is I do not see the language prohibiting the AHJ from permitting the use of a lower non-standard rating.
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This is not a matter of "it's not prohibited, so therefore it is permitted." The language here is fairly clear:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Statement 1: "You shall do this."</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Statement 2: "Instead of that, you shall be permitted to do this other thing."</font>
<font size="2" face="Verdana, Helvetica, sans-serif">That gives you two choices, and no others. It does not permit you to find your own middle ground.

The reason I say that comes from "Statement 1," or more to the point, from 240.4. It clearly requires that we protect conductors in accordance with their ampacity. Subparagraph (B) gives us one alternative, but it does not give us a complete range of alternatives. So if we don't choose to use that specific alternative, we must go with 240.4.
 
Re: Going to the next higher overcurrent divice

charlie b: use the next higher standard overcurrent device rating
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charlie, you do such an excellent job of making me think. I hate to admit how many times over the years I had told folks in similar situations (fixed loads) to go to a 10 amp fuse OR a 15 amp breaker....not using the thought process to which you just opened my eyes,,,,,
Thanks
 
Re: Going to the next higher overcurrent divice

Yeah he is good, but we can't keep telling him so or he will not be able to fit his head into his fancy hat anymore. :D

CoolHat.jpg


[ February 23, 2006, 02:58 PM: Message edited by: iwire ]
 
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