Both the CEC and the NEC have clear and precise guidelines on how to do load calculations. In the CEC, for example, section 8 contains all of the rules and demand factors that are inputs to the calculations used to determine the minimum size a service.
If it was me, I would do a load calculation for the whole facility, using whatever code is in effect in your jurisdiction, then once the total demand is known, do load calculations for each of the zones covered by the three sub panels and then size their feeds as indicated. The calculations for the three zones should roughly equal the total for the whole building, at least they should if the calculations were valid.
By the way... you must mean "120/208v" as there is no such thing as a 120/220V 3ph 4w system.
Best advice... get a pro.
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Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
Is the system a 120/240 (center tap grounded) 4wire DELTA or is it a 120/208 (grounded neutral) WYE?
120/220 4W 3-phase is not an option. The actual voltage is critical to sizing the MDP. Another factor to consider is the characteristic of the load. Are they continuous ( capable of operating more than 3 hours).
Panel rating
Re: Panel rating
