Conductor Sizing Branch Circuits

[Pete at MGC]

On page 107 of Article 210 in Understanding 2014 NEC there is question about conductor sizing. In the latter part or the question, the 80% adjustment jumps to the 90 degree C column, why?

 

[Dennis Alwon]

You can use the 90C column for de-rating purposes if your conductors are rated 90C. 110.14(C)

 

[augie47]

be sure to read all of 110.14. The key to what Dennis states is "for de-rating" purposes.
110.14 will likely require you use the 60 or 75 degree rating of the conductor for over-current
protection.

 

[Pete at MGC]

Thank you! The question in the book only referenced that the terminals were rated at 75C, it never mentioned the wire rating. The question/answer scenario alludes to the ambient temperature by saying it needs to be addressed.