Derate 400amp parallel feed

[benaround]

Do you even need the grounded conductor? Not very often in a/c.

 

[infinity]

If he's using a 90 degree conductor than you're a little off on your derating. #4/0 is rated at 260 amps in the 90 degree column which is used for derating.

260(2)= 520 amp(80%)=416 amps

Since this is a 3 phase feeder, wouldn't we use 70% as a multiplier since we would have 8 current carrying conductors if they were run in parallel?

You wouldn't need a neutral for the Liebert units. And even if you installed a neutral in each feeder, unless you have more than 50% of the load non linear than the neutral would not count as a CCC.