Derating conductors

[john37]

Please excuse my ignornance on this issue about derating conductors. I don't understand on how to do it. I have a situation where I need to run two sets of feeder from a distribution board that is located on the 1st floor. These feeders need to run up to a second floor. The distance is approx. 250 feet. One feeder will be supplied by a 3P150A breaker which feeds an existing wireway and the other feeder will be supplied by a 3P40A breaker which feeds an existing Air Handler. Now instead of running a seperate 2 1/2"C, 4 #2/0, 1 #6 grd for the 3P150A feeder and a seperate 1"C, 3 #6, 1 #10 grd for the Air Handler I wanted to run all the feeders in one conduit which leads me back to my question of how I derate the conductors? Could someone please explain how I do this and if you have any better suggestions to handle these two feeders that would be helpful too. Thanks.

 

[Dennis Alwon]

See if art.310.15 & Table 310.15(B)(2)(a) helps. Remember you can use the 90C column in Table 310.16 for derating purposes.

 

[iwire]

John I am assuming a few things like 6 current carrying conductors total, 90 C conductors.

But even with an 80% derate you wire sizes will work.

 

[john37]

Got it....Thanks guys.