Any electrian worth his salt uses the code book for the base of his calculations. First go to chapter 9 in the code book and use the the examples that will refer you back to the 220 area of the code. Use these for your base, either the standard calculation or the optional. But you must use common sense, and remember the code book calculations are a minimum standard, if you feel that the service that you need is more than the minimum based on continious loads or other factors, you than must increase the service. An example is a motel with PTAC units, do size to a per centage or do size for the worst case, a zero degree day and the motel is full. You as the electrian have to make the decision.
Joe Ogle
