NEC 392.80; Cable Tray Conductor Derates

[rayp1]

Two Questions related to, NEC 392.80(A)(2)a;
Does the code expect an additional deduction of ambient temperature for conductor amp capability?

My example:
-given:
a. single conductor in open cable tray: 300CU = 500amps from T310.15(B)(17);
b. ambient temperature derate of .91 for average high temperature of 100 degree F from T310.15(B)(2)(A)
c. derate for open cable tray with single conductor of .65 from NEC 392.80(A)(2).
d. no issues with cable tray width or space.

Result: 500A x .91 x.65 = 295 amps

Makes sense to include derate for ambient by area, If this is the case should the code add this requirement?

 

[david luchini]

The Table 310.15(B)(17) is based on an Ambient of 86degF. The table tells you to refer to 310.15(B)(2) for ampacity correction factors for ambients other then 86degF.

There is nothing that needs to be added.