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Monday, January 30, 2017
Question:
I have a question for clarification. The installation is using #12 AWG type THWN-2 copper conductors and the terminations are rated 60 degrees C. There are six current carrying conductors, in conduit, running through an attic with an ambient temperature of 132 degrees F.
My calculations are as follows:
Conductor sizing calculations 12 AWG THWN-2 (90 degree C) = 30A
For six current carrying conductors derate 80% 30A x 0.8 = 24A
for ambient temperature of 132oF derate 71% 24A x 0.71 = 17A
The load is 16A. 12 AWG at 60oC is rated 20A the OCPD is rated 20A
The conductors are appropriate for the application.
Would you agree with this? If not please explain.
Thank you, Stan W. Johns, P.E.
A
Answer:
Hey Stan thanks for your question. Your math is correct based on the conditions of use provided and the conductors have an ampacity of 17.04 after applying correction and adjustment factors as stated in 310.15(B). If the conductors are not supplying multiple receptacles then rounding up to the next standard size (20 amperes) in Table 240.6(A) is allowed as stated in 240.4(B).