Two tables now 310.15(B)(2)(a)&(b)

[wireguy8169]

I have a thread about this in the NEC so if a moderator needs to delet the one I understand. Anyhow, I have done my code change course from 2008 to 2011 and this was not discussed, actually till I was preparing a lesson for my class I did not even realize there was two tables in the 2011 code book. I for the life of me can not find an explaination for when to use one table over the other for derating conductor for amb. temp. (other than the obvious 86deg or 104degree) any insight I can get for myself and students would be greatly appreciated.

Thanks

 

[charlie b]

We don't allow duplicate discussions, so I will close this one. The other discussion is here:
http://forums.mikeholt.com/showthread.php/134373-Art.-310-Ambient-temp-tables-2011