Cable sizing for Lighting panel breaker

[nsmithga]

I have an 800A 480V distribution panel that I must size a feeder for.
The maximum continuous current permitted per the NEC for the CB would be 640A. (CB not listed for continuous duty)

My solution would be to size the feeder for 800A which is 125% of the maximum continuous load.

This would be 3 sets of 300KCMIL CU per phase with 3 #4AWG CU grounds.
The cable ampacity is based on the 75 deg C rating, which is what most lugs are listed at.

Am I correct?

 

[charlie b]

You are correct in selection of 3 sets of 300 MCM conductors. But the EGC in each conduit (I infer that each set will go in a separate conduit) must be sized for the overcurrent setting of 800 amps, not of the ampacity of the conductors in each conduit. So you need 1/0 EGC in each conduit. Reference 250.122(F)(1).

Welcome to the forum.