Deration of conductors

[Ken Misal]

Gentlemen, here is a question reguarding the application of derating factors concerning temp. and multiple cable bundling. Asume attic temp 135 degress F, 12-2 nmc cable .Determine the ampacity of #12 conductors in NMB cable when run through an attic over 10 feet and bundled with 6 other cables of the same type(12-2 NMC). The correction factor for temp is 0.71 from table 310-16 and the correction factor for 14 current carrying conductors when bundled is 50% table 310-15 b 2 a. Question is do you need to apply both corrections or only the higher of the two , the 50% for multiple cables?

 

[brother]

Gentlemen, here is a question reguarding the application of derating factors concerning temp. and multiple cable bundling. Asume attic temp 135 degress F, 12-2 nmc cable .Determine the ampacity of #12 conductors in NMB cable when run through an attic over 10 feet and bundled with 6 other cables of the same type(12-2 NMC). The correction factor for temp is 0.71 from table 310-16 and the correction factor for 14 current carrying conductors when bundled is 50% table 310-15 b 2 a. Question is do you need to apply both corrections or only the higher of the two , the 50% for multiple cables?

Yes you apply both. I dont know of any exception to the derating of conductors. also heres a link to derating, its a good article.

http://www.iaei.org/subscriber/magazine/00_b/pauley.htm

 

[Ken Misal]

Thanks for the quick response and the link , just checked it out and found it very informative. This was a topic of discussion this morning and as usual we had a split decision. I was just not sure of the double deration. Thanks again.