Ampacity Correction Question

[A-1Sparky]

Let's say that after correcting for ambient temperature and bundling, you end up with an allowable ampacity of 70 amps for #6 THHN (using the 90C rating in table 310.15(B)(16)). However, the terminal lugs in the circuit are only 75C-rated, so the load (if noncontinuous) must be 65 amps or less (according to table 310.15(B)(16)). Is this correct?

 

[jumper]

Yep. 110.14(C).

 

[A-1Sparky]

So, basically, anytime the corrected ampacity (from ambient temp. and bundling) ends up higher than the 75C rating you have to use the lower ampacity rating of the terminations?

 

[charlie b]

That is correct.

 

[jumper]

In short, final ampacity of a circuit is determined by its weakest link.

 

[Dennis Alwon]

Let's say that after correcting for ambient temperature and bundling, you end up with an allowable ampacity of 70 amps for #6 THHN (using the 90C rating in table 310.15(B)(16)). However, the terminal lugs in the circuit are only 75C-rated, so the load (if noncontinuous) must be 65 amps or less (according to table 310.15(B)(16)). Is this correct?

I agree with the others however if the load is 65 amps or less it may be allowed on a 70 amp breaker. 240.4(B)

 

[A-1Sparky]

Thanks for the confirmation guys. I'm using Mike Holt's study guide to prepare for my master's exam and this situation isn't clarified in the section regarding ampacity correction. Thanks again for the quick responses.

 

[david luchini]

Thanks for the confirmation guys. I'm using Mike Holt's study guide to prepare for my master's exam and this situation isn't clarified in the section regarding ampacity correction. Thanks again for the quick responses.

Take a look at 215.2(A)(1) for feeders and 210.19(A)(1) for branch circuits for clarification. Both say a circuit with a non-continuous load of 66Amps (75deg C terms) would need to have minimum #4 THHN conductors even if the corrected/adjusted ampacity of #6 is 70.

 

[A-1Sparky]

Thanks, David. :thumbsup: