Phase Converter Sizing

Use the largest motor's rating (usually spindle).
Load Type / Application
Recommended Rotary Phase Converter
--
HP RPC
Based on a safety factor of --x for your load type.
1-Phase Breaker
-- Amps
Idle Current
-- Amps
RPC Sizing Guide

A Rotary Phase Converter (RPC) uses a 3-phase idler motor to generate a 3rd leg of power. To start your machine's motor, the RPC must be significantly larger than the motor it's starting.

Key Rules:
  • The 2-for-1 Rule: For heavy starting loads or CNC machines, use an RPC with 2x to 3x the HP of the largest motor.
  • Total HP: An RPC can run multiple machines at once, as long as the largest single motor doesn't exceed its starting capacity.
  • Voltage: Residential 1-phase is 240V. Your RPC will output 240V 3-phase. If you have a 480V machine, you will need a step-up transformer.
CNC Warning

CNC machines contain sensitive electronics. Ensure you buy a "CNC Rated" RPC or a digital phase converter to ensure the generated 3rd leg is voltage-stabilized.

Pro Tip: Oversizing an RPC is rarely a problem, but undersizing it will cause voltage drops that can blow fuses or trip CNC logic boards.