Depends on which amps you're talking about.
Power consumption (overhead) for the RPC idler motor is about 12%, assuming good power factor (> 0.7). So that amount of power or energy is wasted using an RPC.
You can figure amps from the conservation of power law: power in single phase = power in three phase.
Amps in single phase = 1.732 X amps in three phase.
So, say you've got a 5 hp mill running off a 7.5 hp idler, well balanced.
At full load, three phase (nameplate) amps should be around 10 amps (746watts/hp X 5hp / 240 volts / 1.732 = 8.97 amps).
By above formulas, single phase amps will be 10 amps X 1.732 = 17.3 amps (from the two 240 volt single phase lines feeding your RPC idler).
Figuring 12% wastage for the idler overhead, you get 17.3 X 1.12 = 19.4 amps single phase.
You need at least a 20 amp breaker to feed that RPC, and it better be HACR-rated to take the starting current.
[This message has been edited by bnelson (edited 08-12-2004).]