XHHW 75C? OR 90C?

[Tomcdi03]

A question regarding conductor ampacity was associating 750 MCM conductors 6 of them in a conduit 22° C ambient temperature for the maximum allowable ampacity I'm confused why many of the conductors have multiple temperature ratings like.
THHW . Can somebody please explain this the only thing I can assume is that if the question asks for the maximum allowable ampacity then I would automatically use the higher temp rating. What situation would we use 75C?

 

[jumper]

You can use the max for adjustments and correction factors, but your final ampacity will be limited to being no higher than the terminal rating, often 75C.

Check out 110.14

 

[Carultch]

A question regarding conductor ampacity was associating 750 MCM conductors 6 of them in a conduit 22° C ambient temperature for the maximum allowable ampacity I'm confused why many of the conductors have multiple temperature ratings like.
THHW . Can somebody please explain this the only thing I can assume is that if the question asks for the maximum allowable ampacity then I would automatically use the higher temp rating. What situation would we use 75C?

Some of these wire types are rated for 90C in dry locations and only 75C in wet locations. For XHHW, this is a thing of the past, as most if not all XHHW you'll get today is actually dual rated as XHHW-2, which is 90C rated in both wet and dry locations.

 

[jumper]

Hold on, I was thinking of something similar but just realized your question.

For conductors that in both columns like that, 75C is when used in a wet location and 90C is for a dry location.

These are your starting ampacities before any adjustments.

 

[Dennis Alwon]

I am a bit confused as to what you are asking. Conductors have different insulation based on conditions of the job. For instance, a wire that is used in wet location must have the letter "W" in the label.

The temperature rating can vary from 60C to 75C to 90C. I am not sure if I can say why all conductors aren't rated 90C. It is the nature of the beast and quite frankly most of the standard conductors are rated 90C. Of course, you are still limited to 75 C because of the rating of the equipment- which is usually 75C

 

[infinity]

Also if this is a test question then you must accurately determine the 60°, 75° or 90° ampacity even if it's a somewhat obsolete insulation type.

 

[luckylerado]

Check out Table 310.104(A) for more info.