Conductor sizing

[JdoubleU]

When derating conductor size due to ambient temp for THHN do you use the 90 degree column?

 

[mcclary's electrical]

When derating conductor size due to ambient temp for THHN do you use the 90 degree column?

yes.......

 

[Dennis Alwon]

I agree, however the final amp. cannot be larger than the weakest link. In most cases that would be either 60C (NM cable) or 75C (most terminals).

 

[charlie b]

I don't have my book handy, but I think the reference is 110.14(C).

 

[Dennis Alwon]

I don't have my book handy, but I think the reference is 110.14(C).

Not bad for an old man.

110.14(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.