NEC 310.15(B)(2)(a) Ex 5

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erickench

erickench

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I've read the above exception in the NEC and I see a potential omission. It states that adjustment factors shall not apply to Type AC or to Type MC cable when conductors are No. 12 AWG. Is this just for No. 12 AWG? What if it's larger than No. 12 AWG? What if it's smaller than No. 12 AWG? Am I missing something here?
 
If you are missing something, then you are not alone. I can't tell if the phrase "under the following conditions" is intended to mean "any of the following" or "all of the following."
 
It is my understanding that this exception was based on actual physical testing and they only tested MC with #12 conductors so it only applies for #12s. It is my opinion that the exception only applies if you meet all of the conditions listed.
 
It's just for #12's and as Don said they must meet all of the conditions listed in the exception.
 
Yes but don't you think its kind of strange that the wording is'nt:

"larger than or equal to No. 12 AWG"

or

"smaller than or equal to No. 12 AWG"

I mean it's weird. Why just No. 12 AWG?
 
Because an engineer would see that this is a problem. You can't just single out one AWG size and not include any of the rest. It either has to be the smaller sizes or the larger sizes. I would need more information about this test and how they came to writing this NEC rule.
 
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erickench said:
Because an engineer would see that this is a problem. You can't just single out one AWG size and not include any of the rest. It either has to be the smaller sizes or the larger sizes. I would need more information about this test and how they came to writing this NEC rule.
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This exception was the result of proposal 6-67 for the 2002 code and was submitted by a representative of the National Armored Cable Manufacturer's Association. Part of the substantiation says that the exception is limited to #12 because that is what was covered by the test report. It had been submitted as 6-90 for the 1999 code and was rejected.
 
Well they are going to have to expand on it. Either to include the larger sizes or the smaller sizes. I would say the smaller sizes(>=No.12). They take up less room therefore the conductors have more surface area for heat dissipation.
 
I say so. It's too late to submit proposals for the 2011 NEC. But maybe next time. I'm not a certified inspector. But I used to inspect construction projects for the city of NY.
 
George Stolz said:
MC cable without a PVC jacket over what we'd normally envision, I believe.

http://www.shawflex.com/products/products_typeMC.htm
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I thought that too, but it seemed a little vague.

If this is the case, derating doesn't really apply at all to most installations with MC cable, at least until you get over 20 conductors. That seems hard to believe. I have a feeling an inspector will interpret that article differently, and still require derating over 3 ccc if bundled. I think I'd definitely ask my inspector first.
 
erickench said:
Well they are going to have to expand on it. Either to include the larger sizes or the smaller sizes. I would say the smaller sizes(>=No.12). They take up less room therefore the conductors have more surface area for heat dissipation.
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I doubt that the exception would be expanded unless the submitter of the proposal to do so submits a fact finding report from UL or similar organization supporting the proposal. That is how this one got in and even with the fact finding report it did not make it into the code the first time it was proposed. If the submitter of the proposal that resulted in exception #5 does not commission another fact finding report to expand the exception I don't think anyone else would spend that kind of money on this issue.
Proposals for the 2014 code are due the first Friday of November, 2011. If someone wants to get it in the 2014 code they need to be talking with a testing agency about a fact finding report very soon.
 
don_resqcapt19 said:
I doubt that the exception would be expanded unless the submitter of the proposal to do so submits a fact finding report from UL or similar organization supporting the proposal. That is how this one got in and even with the fact finding report it did not make it into the code the first time it was proposed. If the submitter of the proposal that resulted in exception #5 does not commission another fact finding report to expand the exception I don't think anyone else would spend that kind of money on this issue.
Proposals for the 2014 code are due the first Friday of November, 2011. If someone wants to get it in the 2014 code they need to be talking with a testing agency about a fact finding report very soon.
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I say so. It's too late to submit proposals for the 2011 NEC. But maybe next time. I'm not a certified inspector. But I used to inspect construction projects for the city of NY.
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Not even if he say's so ? :D
 
Cow said:
I thought that too, but it seemed a little vague.

If this is the case, derating doesn't really apply at all to most installations with MC cable, at least until you get over 20 conductors. That seems hard to believe. I have a feeling an inspector will interpret that article differently, and still require derating over 3 ccc if bundled. I think I'd definitely ask my inspector first.
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IMO the inspector is not permitted to interpret this his way. It says what it says. When all of the conditions are met, you're correct, the first 20 CCC's require no derating.
 
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