How to deliver 450KW of power?

Parallel conductors are used to supply current when the largest available conductor is not large enough or when two or three smaller conductors are more convenient to install. There are also busway products that carry current using copper or aluminum bars enclosed in a metal duct.

Above 480 volts, standard utilization voltages are 575 volts, 2300 volts and 4160 volts in the USA and Canada. In the USA, 575 volts is not used very much, but it is used in preference to 480 volts in Canada. Users of voltages of 480 volts and higher would generally be supplied 3-phase power from a transformer located on the customer's property. Either the utility or the customer might own the transformer.

It varies. It depends on what is available in the street near you, on on the poles. Usually about 6kV. But I don't think you have to go above 480.

My condo building has 120/208 3 phase at 800 amps per phase, or a total of 288 kW

A 277/480 volt 800 amp 3 phase service would deliver 664 kW, easy to do. And most commercial heavy equipment can be bought setup for 480 volts, or 277 volts.

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