75 vs 90 degrees

[mshields]

What is it that governs our using the 75 degree column in 110.15(B)16 for over 100 and up? And under what circumstance could you use the 90 degree column?

The reason I ask is that I recently ran into the a 2000A feeder from one UL 1558 switchgear to another 1558 switchgear for which the cable used, 4 sets of 600kcmil doesn't get you to the breaker setting; 2000A.

Could be that the breaker needs to be set lower. If so, it never was and maybe that's what I need to advise them to do. I do know that even at 90 degrees, 600's are only rated for 470A, so that doesn't get me to the 2000A either.

Still, it prompted me to ask the question.

Thanks,

Mike

 

[augie47]

Field wiring or factory ?
Using a standard building conductor you are correct that there is not a provision that would allow 600s at 2000 amp but since you were running between UL switchboards there might be a conductor that was approved

 

[ron]

Even 1558 SWGR is tested at 75 deg terminations. Without an intermediary termination box at either end, you are stuck at 75 deg ampacities.

 

[electrofelon]

I very frequently see older installations where they presumably used the next size up rule over 800 amps, and/or used the 90 degree ampacity. How old is this?

 

[mshields]

brand new

brand new

good to know Ron.

This is only a few years old so shouldn't be by any particularily old codes. And definitely field wired so...

Thank you gentlemen!