I have a 4 inch pvc conduit that is underground going to a tran socket which then goes to a 400-amp disconnect that is fused at 400-amps. They are showing me on the drawings to pull 2 sets of 4-3/0 in the same conduit do you have to derate them as per 310-15 and if so what would you pull in that conduit. The voltage is 480/277 3 phase 4 wire service.