Ampacity Correction Factors

[kevin458]

I have question about ampacity correction factors. In calculating conductor sizes using Table 310.16, we apply the correction factors of Table 310.15(B)(2)(a). Will it be Ok if I apply the correction factors on load current (instead of on the ampacity values of Table 310.16)?

For example for a 30 HP 3-Phase 460V motor the current is 40A. If there are 10 conductors in the tray, then from table 310.15(B)(2)(a) the correction factor is 0.5. So the uprated current of the motor for conductor calculations is 40/0.5= 80 A. So a #4 THW cable is required.

Is this approach Ok, what do you guys think?

 

[iwire]

It seems backward to me but I don't see why it would not work.

You still need to figure 125% of the real motor current into it.

 

[infinity]

Are all 10 conductors CCC's?