310.16 question

[billdozier]

When using 310.16 do you use the 75 or 90 degree table for thwn. I was under the impression that the breaker being rated 75 degrees dictates that we use the 75 table. Am I wrong? If so where does the breaker rating come into play? Thanks guys

 

[Twoskinsoneman]

When using 310.16 do you use the 75 or 90 degree table for thwn. I was under the impression that the breaker being rated 75 degrees dictates that we use the 75 table. Am I wrong? If so where does the breaker rating come into play? Thanks guys

If you do some searching you may (even with the PATHETIC search functions offered by this forum) find many threads that answer this question. Check out 110.14(C). Basically you can use the highest temp-ampacity of the the wire you are using (in the situation it is being used) UP TO the lowest temp rated device connected to it.


edited to add: BTW given the current marketed equipment this will almost always be the 75 degree column for thhn/thwn

 

[Smart $]

...
edited to add: BTW given the current marketed equipment this will almost always be the 75 degree column for thhn/thwn

For maximum cirucit ampacity, yes, the 75?C column. You are stuck with the 75?C column value when used in a thwn capacity. But when used as thhn, you can apply ambient and derating correction factors to the 90?C column ampacity of the conductor, but the circuit ampacity can never exceed that of the 75?C column value.

 

[480sparky]

Temperature ratings for various insulation types are listed in T310.13(A).

 

[Twoskinsoneman]

the circuit ampacity can never exceed that of the 75?C column value.

I wouldn't say never. There are terminals rated 90 degrees but they are not as common.....but I wouldn't say non-existing.

 

[resistance]

I wouldn't say never. There are terminals rated 90 degrees but they are not as common.....but I wouldn't say non-existing.

I agree!!!!

 

[raider1]

I wouldn't say never. There are terminals rated 90 degrees but they are not as common.....but I wouldn't say non-existing.

I am not disagreeing with you but keep in mind that sometimes a lug might be listed for 90 degrees but the equipment that the lug is connected to might not be listed for 90 degrees, such as in switchgear.

Chris

 

[infinity]

I am not disagreeing with you but keep in mind that sometimes a lug might be listed for 90 degrees but the equipment that the lug is connected to might not be listed for 90 degrees, such as in switchgear.

Chris

I agree that you may find a 90 degree lug but you probably won't find much equipment that is rated for 90 degree lugs operating at 90 degrees.

 

[Twoskinsoneman]

I am not disagreeing with you but keep in mind that sometimes a lug might be listed for 90 degrees but the equipment that the lug is connected to might not be listed for 90 degrees, such as in switchgear.

Chris

I agree that you may find a 90 degree lug but you probably won't find much equipment that is rated for 90 degree lugs operating at 90 degrees.

I agree with both of you. I was just saying it was not impossible. I remember quite a while ago a discussion about running a very long circuit you could ,in theory, run a middle section of the circuit at the 90 degree ampacity (if the splices were rated as such) and then from the splice to the equipment a short piece run at the 75 degree ampacity.

Don't know if it would ever be profitablt but just an example of a possibility.

 

[stars13bars2]

We need to get some more information to determine where the requirements of 110.14(c)(1) will put you. There is a good chance it could be 60? C column.

 

[Dennis Alwon]

When using 310.16 do you use the 75 or 90 degree table for thwn. I was under the impression that the breaker being rated 75 degrees dictates that we use the 75 table. Am I wrong? If so where does the breaker rating come into play? Thanks guys

Bill just remember that your circuit temp. rating is defined by the weakest link anywhere in the circuit. Thus nm cable that has 90C wire inside the jacket must still be installed at the 60C rating because of 334.80.

 

[Smart $]

I wouldn't say never. There are terminals rated 90 degrees but they are not as common.....but I wouldn't say non-existing.

True... but my response was based on the OP stating the breaker [termination] was rated 75?C.

 

[Twoskinsoneman]

We need to get some more information to determine where the requirements of 110.14(c)(1) will put you. There is a good chance it could be 60? C column.

What do you mean? Why do you say there is a good chance it will be 60 degree.

Here's the info we have.
thhn
75 degree CB