The only time you can use the 90 C column is to start your derating calculations.

You will need to use the 75 C column and 3/0 copper for a 200 amp commercial service.

If the calculated load is under 180 amps you could also use 4/0 AL.

Glad to see you stuck around. [Linked Image]

Bob

Bob Badger
Construction & Maintenance Electrician
Massachusetts