# NEC Table 310.15(B)(2)(a) and (b)



## AAGR2013 (Oct 13, 2016)

If I have rated 90 degree #12 THHN runs in ambient 55 degree, the capacity is 30A based on 310.15(B)(16). Because it is used in 55 degree, the factor need to multiply. If use (a), the factor is 0.76, however if use (b), the factor is 0.84, which one shall I use?


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## allgood (Oct 13, 2016)

Depends on which table you're using for the conductor size/rating. What's the exact question you're trying to solve? You want to match the ambient temperature rating of the wire to the table.  Let me know what the problem is and I can clarify. I had the same issue last month and figured out which one to use (typically it ends up being B2a).


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## knight1fox3 (Oct 13, 2016)

AAGR2013 said:


> If I have rated 90 degree #12 THHN runs in ambient 55 degree, the capacity is 30A based on 310.15(B)(16). Because it is used in 55 degree, the factor need to multiply. If use (a), the factor is 0.76, however if use (b), the factor is 0.84, which one shall I use?


If you're referencing Table 310.15(B)(16) for allowable conductor ampacity, double-check the title of the table. It indicates that the corresponding ampacities are based on an ambient temperature of 30 deg. C. So the 30 deg. C adjustment factor table (2)(a) should be used.


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## AAGR2013 (Oct 13, 2016)

I need new glasses :reading:


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