Ampacity ?

[Jody Meulemans]

What is the maximum allowable ampacity for a #1awgTHHN copper conductor ran behind a boiler with an ambient temperature of 136 degrees F? I've had two answers. One being 106 amps. The other being 75.48 amps. Which one is right?

 

[infinity]

How did you arrive at those answers?

 

[one_eyed_jack]

From what I understand, THHN run in a dry location is to be sized at 90C and in a wet location at 75C for conductor ampacity calcs unless there are terminals involved in which case it's a little different. Since the question does not specifically say dry or wet, I think you have to use the dry rating of 90C. #1 THHN at 90C is rated 150A. Multiply this by the correction factor of .71, and you end up with 106.5A.

I'm not 100% on this but from what I can gather from the question, I believe 106.5A is the correct answer.

 

[one_eyed_jack]

I may have explained that wrong. I was thinking THHW for wet and dry, not THHN. I still think the answer is 106 since you would use the 90C rating of THHN in this question as there is no device and you are simply calculating the maximum allowable ampacity of the conductors for the problem.

 

[chris kennedy]

Multiply this by the correction factor of .71, and you end up with 106.5A.

I'm not 100% on this but from what I can gather from the question, I believe 106.5A is the correct answer.

I believe this supports the above answer.

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.

 

[SEO]

What percent of the circuit is in the 136 degree temp? Might be able to apply section 310.15 (A) (2).