310.15(B)(2)(a) Exception 5

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blueheels2

Senior Member
Location
Raleigh, NC
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Electrical contractor
Could someone please help me to understand this.

Ex 5. Adjustment factors shall not apply to type AC cable or to type MC cable w/o an overall outer jacket under the following conditions:

Is this saying that adj. factors don't apply to AC cable at all and they don't apply to MC cable w/o an overall outer jacket or the adj factors don't apply to AC or MC w/o an overall outer jacket.

Also AC or MC cable w/o an overall outer jacket wouldn't really be AC or MC.

It seems to me that this exception would allow you to stuff the holes in metal studs with 6 12-3 and one 12-2 cable since this would keep you under 20 current carrying conductors.

What am I missing or misunderstanding?

Thanks for the help!!!!
 
blueheels2 said:
Also AC or MC cable w/o an overall outer jacket wouldn't really be AC or MC.
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By 'overall jacket,' they're referring to a skin like LFMC has, not the armor itself.

The wording of the exception refers to any AC cable or unjacketed MC cable. Apparently, only MC is available with a jacket.
 
So does this exception allow you to put as many cables as will fit in the stud holes as long as the current carrying conductors do not add up to more than 20. The reason I bring this up is because the inspector here does not want any more than 3 pulled together without derating.
 
derating

derating

when ac or mc cables are stacked together they create heat and they extend exceeding 24"you must derated.same rule applies to conductors in a raceway.
 
i have not shown it to the inspector. This happened on Thursday and I had Friday off. I was just researching to see where the inspector was getting this from. It seems to me that this exception allows you to not derate with less than 20 current carrying conductors in mc or ac cable w/o the overall outer covering. If my understanding is correct I will probably bring it up the next time I see him. Not to rub it in but just to see his take on it.
 
blueheels2 said:
If my understanding is correct I will probably bring it up the next time I see him. Not to rub it in but just to see his take on it.
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Decide early on whether you want to take a firm or flexible position on the matter, and stay consistent.
 
blueheels2 said:
So does this exception allow you to put as many cables as will fit in the stud holes as long as the current carrying conductors do not add up to more than 20. The reason I bring this up is because the inspector here does not want any more than 3 pulled together without derating.
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This should'nt be an issue with the inspector. The exception is quite liberal. Providing all the requirements are met, a 60% derate won't effect most runs. There are very few circuits that are loaded that close to the rating of the breaker that the next higher can't be applied.

Rick
 
RUWired said:
This should'nt be an issue with the inspector. The exception is quite liberal. Providing all the requirements are met, a 60% derate won't effect most runs. There are very few circuits that are loaded that close to the rating of the breaker that the next higher can't be applied.

Rick
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60% for #12 conductors leaves you with 18 amps. For multiple receptacle circuits you're stuck with a 15 amp OCPD not a 20 amp OCPD. Going up to the next standard size is not permitted.


Also 310.15(A)(2)Exception would cover cables run through holes in the studs.
 
RUWired said:
Because of 240.4(B)1?
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Yup, I know that you mentioned all the exceptions being met but I have heard some guys say that 310.15(B)(2)(a) Exception 5 removes any real restrictions from bundling AC and MC cables. You still need to go beyond that code section and comply with, as you've said, 240.4(B)(1).
 
infinity said:
Yup, I know that you mentioned all the exceptions being met but I have heard some guys say that 310.15(B)(2)(a) Exception 5 removes any real restrictions from bundling AC and MC cables. You still need to go beyond that code section and comply with, as you've said, 240.4(B)(1).
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I respectfully disagree with you. 310.15 (B)(2)(a) gives you a very specific condition that derating is limited to 60% and says nothing about "unless stated anywhere else in the code" So I don't see how you can say that 240.4(B)(1) overrides this, if it did the CMP would have, or should, remove 310.15 (B)(2)(a) from the code.
 
acrwc10 said:
I respectfully disagree with you.
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I agree with Rob, there is nothing in the exception that allows you to ignore anything in any other Article of the code. It can not, an exception only applies to the section directly previous.

If an exception effects multiple sections you will find an something about it in each section needed.

For instance, the exception to 408.40 is specifically referenced by 250.146(D)
 
iwire said:
I agree with Rob, there is nothing in the exception that allows you to ignore anything in any other Article of the code. It can not, an exception only applies to the section directly previous.

If an exception effects multiple sections you will find an something about it in each section needed.

For instance, the exception to 408.40 is specifically referenced by 250.146(D)
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Then when could you ever use the Ex, 310.15(B)(2)(a) ? It is simply not applicable then.
 
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