Why am I talking about FLA? That is a good question.
At the start of this thread you indicated that you had a 50 HP Baldor motor for an idler that you intended to pony start. The single-phase power to the motor was going through a 200 amp contactor. There is no mention of what the RPC will be powering, or what the available electrical service is.
You are using a pony start RPC to reduce the starting inrush current. In my first post (#7) I mentioned my experience with having capacitors in the circuit while using a pony motor and finding that sometimes the inrush current was increased instead of decreased. I used a reference to this as a multiple of the FLA as it is an easy way to calculate what could happen with a different motor.
Where I got “off” was in post #14. The NEC uses FLA as a way to specify the required conductor size, overload protection, and disconnect size for phase converters. BUT- this is the FLA stated on the manufacturer nameplate on the phase converter, not the nameplate on the idler motor. My calculations based the idlers FLA --ARE NOT-- appropriate for a pony start RPC.
Because you are “manufacturing” your own phase converter, you can design it to your own specifications and create your own nameplate.
What the NEC wants that nameplate to have are: Manufacturer’s name, input and output voltages, HZ, rated single-phase input full load amps, rated minimum and maximum single load in kVA or HP, Maximum total load in kVA or HP, and for a RPC, 3 phase amps at full load.
You have some decisions to make. If you can safely do so, wire up your components, try it out, and measure what actually happens in starting the RPC, and what amps it uses at idle.
Decide the maximum HP motor you will start. Keep in mind that your RPC will have the full inrush current of any motor started, in addition the running current of the RPC, and the running current of any additional motors running at the time.
FYI
I have read many times that the inrush current is typically 5 or 6 times the FLA. I just tried to confirm this, and it is used as a rule of thumb- but to accurately calculate it you use the locked rotor letter code stamped on the nameplate to tell you the locked rotor kVA per HP, multiply this by the Nameplate HP and calculate the amps based on the voltage supplied.