I have an application with 1000A continuous load with the conductors installed on a cable tray. So to support 1000A continuous, I need a 1250A CB. Based on 392.80(A)(2)(a), the ampacity shall not exceed 75% of ampacities listed in 310.15(B)(17). Using 90C column (assuming I could utilize 90C if insulation is rated for 90C), 700kcmil is rated for 850A. (At this point I would apply temperature derating if I have to, and check against 1000A load I am trying to support). Two sets are good for 2x850x.75=1,275A. Since the cable will be terminated at the CB with 75C rating, I take 75C column rating and compare it to CB rating: 755x2=1510 which is greater then the CB rating so I should be OK.
My question is how 110.14 applies to this. Based on 110.14, I need to use 310.15(B)(16) 75C rating instead of 310.15(B)(17) 75C rating for the last step above which doesn't make any sense to me.
thanks in advance
My question is how 110.14 applies to this. Based on 110.14, I need to use 310.15(B)(16) 75C rating instead of 310.15(B)(17) 75C rating for the last step above which doesn't make any sense to me.
thanks in advance