90C wire 75C Breaker

[wireday]

If my #12 thhn is 90C, and the Breaker Im going to be using is 75C do I start my derating at 30 or 25amps? do they make 90c Breakers? thanks

 

[david luchini]

If my #12 thhn is 90C, and the Breaker Im going to be using is 75C do I start my derating at 30 or 25amps? do they make 90c Breakers? thanks

You can start your derating (ampacity adjustment and correction) at 30Amps. See 110.14(C).

 

[Mulrooney]

I don't think anyone makes a termination rated for 90c. Always thought 110.14(C) should be with the 310. tables. Be less confusing. Just Saying.

 

[jim dungar]

I don't think anyone makes a termination rated for 90c...

It is a fact: UL does not list any LV (600V max) overcurrent protective device termination for use with the 90?C ampacities.

 

[Smart $]

I don't think anyone makes a termination rated for 90c. Always thought 110.14(C) should be with the 310. tables. Be less confusing. Just Saying.

There are plenty of 90?C-rated terminations... just none in manufactured assemblies containing distribution or control equipment.

 

[DBoone]

You would derate from 30A, get your ampacity, then compare to the 75C column and use the smaller of the two as our final ampacity correct?

 

[DBoone]

You would derate from 30A, get your ampacity, then compare to the 75C column and use the smaller of the two as our final ampacity correct?

...but not necessarily the "allowable ampacity"

 

[Smart $]

...but not necessarily the "allowable ampacity"

In NEC speak, allowable ampacity is the ampacity table value for the conductor.

 

[DBoone]

In NEC speak, allowable ampacity is the ampacity table value for the conductor.

Thanks Smart :thumbsup: Keep me straight

 

[DBoone]

What I meant was even if 75C (25A) was the ampacity one still could be limited to a 20A OCPD. Of course you and most others on here know that but I was mainly just throwing that out there to make sure I was correct.