derating

[sleepy]

question, if i have 8 400kcmils and 1#1 ground going in 4"conduit. table 310.16.
75 degree cable at 400kcmil you have 310 time 2 = 670 time .7 = (70%)=469amps i am told by a electrician that the code sayes when you derate you can use the 90 degree column which gives you 380 times 2= 760 = 532amps is this correct and where does it say that.
thank you for your help.

 

[charlie b]

Re: derating

It is true. 110.14(C).

 

[iwire]

Re: derating

It is true if the conductor in question is rated 90 C. Keep in mind if the conductor happens to be installed in a wet location (underground for example) it may have to treated as a 75 C conductor depending on the specific insulation type.

Edit in 'underground'

[ February 15, 2006, 04:32 PM: Message edited by: iwire ]