I've come across the statement many times, that one can use the 90 deg column of 310.15(B)(16) (2017) for derating.
I've also heard that one must use the 75 degee column even if one is using a 90 degree conductor, due to all normally available equipment bring 75 C rated (including the vast majority of lugs)
I have a 275 A load, which is 344 A at 125%. I wanted to use 400 MCM but have been told that I need to use 500 MCM. So I am a bit confused here. What's the correct wire here, and what's the point of even having a 90C column of I always have to refer to the corresponding 75C value?
I've also heard that one must use the 75 degee column even if one is using a 90 degree conductor, due to all normally available equipment bring 75 C rated (including the vast majority of lugs)
I have a 275 A load, which is 344 A at 125%. I wanted to use 400 MCM but have been told that I need to use 500 MCM. So I am a bit confused here. What's the correct wire here, and what's the point of even having a 90C column of I always have to refer to the corresponding 75C value?