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What is a split-phase motor?

A split-phase motor, also known as a split-phase induction motor, is a type of AC electric motor used for medium-duty applications including air conditioning, conveyors and pumps. A split-phase motor has a main winding plus a starting or auxiliary winding and is able to run at constant speed under varying loads.

When the motor is energised, current flows through the starting winding which is in phase with the line voltage. However, current passing through the main winding lags behind line voltage due to its lower resistance and higher reactance. This lag splits the single phase AC power as it creates a 30° phase difference between the currents in each winding. This phase difference produces a rotating magnetic field which causes the rotor to turn.

Here at Gibbons, we supply two versions of the split-phase motor: capacitor start motors and permanent split-capacitor motors.

Capacitor start motors have a starting capacitor placed in series with the start-up winding. This creates a greater phase shift (and therefore much larger starting torque) than split-phase motors.

Permanent split-capacitor (PSC) motors employ only a run capacitor with a high voltage rating which interrupts charge to the start-up winding. The start-up winding then becomes an auxiliary winding once the motor achieves running speed.

The advantages of a split-phase motor include:

  • Reversible at low speed
  • Rapid acceleration
  • Low cost

To enquire capacitor start or permanent split-capacitor motors, or any of our AC electric motors, please call Sales Manager Paul Scott on 01621 868138 or email

Electric Motors

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