master66
If derating is required because of more then 3 current carrying conductors or high ambient temperature, this changes the ampacity of the conductors. The ampacity after derating must be equal or greater then the numbers in my earlier post. This in not new. Table 310-16 ampacities are only for 3 or less conductors and an ambient of 30°C. If your grounded conductor is in fact a current carrying conductor, then you would have to use conductors with a table ampacity of 438 amps for a 400 amp service. This would require 600 kcmil or parallel 3/0s in seperate conduits, or parallel 4/0s in a common raceway. The wire sizes I have listed assume a 90°C insutlation.
Don
