So it is becoming clear that at my level of knowledge the accurate operation of what I call a "branched" RPC system cannot be calculated - too many complicating factors. Therefore I go ahead with the knowns and make allowances.
How does this sound? The load is a 10 HP 3 phase motor. The motor will be operating through a 3 phase transformer to convert the RPC idler voltage to the 460 volt range. I will need to check the data plate of the actual motor but a generic 10 HP motor requires 27 amp at 230 volt and 14 amp at 460 volts.(
Three Phase Electrical Motors)
The idler motor is 15 HP operating at 230 volts. This is a little less than usually desired for a 10 HP motor but the load is a lathe with a clutched drive so the motor will be starting under low load.
Under full load conditions the 230 volt current into the transformer will be approximately the FLA of the load motor at 230 volt (some losses here probably) so I will need 27 amp wire capacity into the transformer and 14 amp capacity from the transformer to the load motor. From the reference this would be #8 wire in and #12 wire out. On a branched circuit the idler basically deals with only the generated phase current so #8 wire in and out of the idler should be sufficient. This leaves the wiring from the supply to the terminal block which distributes power to the transformer and the idler, because of the various losses the current carried will be 1.73 times the FLA, about 47 amps. From the reference this would require #4 wire.
For economic and practical wiring reasons the RPC control unit and idler motor should be as close to the main supply panel as possible. Ditto the transformer. This allows the longer runs of wire to the load motor to be made with lighter gauge wires. As a practical matter the RPC control panel will only be about 6 feet from the main supply panel so #4 wire should be OK. The idler motor will only be about 6 feet from the control panel so #8 wire should be OK for this connection. Ditto, the transformer will only be about 6 feet from the control panel. I will use #10 wire for the connection from the transformer to the machine instead of the calculated #12.
The transformer is rated at 15 KVA.
Starting the idler motor requires thought. A commercial panel such as the Phase Craft would be convenient but a pony motor may be easier on the power supply.
Please suggest any modifications that you feel are required to this plan. Particularly, is the size of the wire from the supply to the idler motor chosen correctly and I can't help thinking that there should allowances for motor start surge somewhere?