I'm told that I'm double derating per 210.20a, this is the way I select THHN.
Say a 125A load.
Continuous load 125A X 1.25 = 156.25A
156.25A/.8 (310.15B2a) = 195.3A so from 310.16 90C get 2/0 THHN. Some might argue the .3A pushes it to 3/0 but I know not 100% continuous load.
Then checking for 70C termination 156.25 < 175 so 2/0 is good.
I'm told this is double derating and should use load and not continuous load 125A/.8 (310.15B2A) = 156.25A applied to 90C get 1/0 THHN. But this makes no sense to me in that this is what I would have selected without the 310.15B2A derating.
Say a 125A load.
Continuous load 125A X 1.25 = 156.25A
156.25A/.8 (310.15B2a) = 195.3A so from 310.16 90C get 2/0 THHN. Some might argue the .3A pushes it to 3/0 but I know not 100% continuous load.
Then checking for 70C termination 156.25 < 175 so 2/0 is good.
I'm told this is double derating and should use load and not continuous load 125A/.8 (310.15B2A) = 156.25A applied to 90C get 1/0 THHN. But this makes no sense to me in that this is what I would have selected without the 310.15B2A derating.
