630.12(b)

[chevyx92]

Under this article you can size your OCP up to 200% of the conductor ampacity. Are you allowed to use the 90 degree column for this or do we stay with the 75 degree column? Example: 3 Phase, 208V, 60 Amp welder. If you use #6 thhn under the 75 degree column it's good for 65 amps. 200% of that is 130 so you could potentially use a 125A breaker right? Now #6 is good for 75A under the 90 degree column and 200% of that is 150. I don't think 110.14(C) allows the use of the 90 degree column for this, but just want to make sure I'm understanding this correctly.

 

[Dennis Alwon]

I would agree with you and say that you must use the 75C ampacity .

 

[Chamuit]

Why would you want or need to do this? Just curious since I have never seen this applied.

 

[iwire]

Why would you want or need to do this? Just curious since I have never seen this applied.

You never need to, you can always run full size conductors. But the NEC will allow you to reduce the conductor size and that may be worth doing if moneys tight.