AB: Represents rotor power input, which divided by synchronous speed equals starting torque.

Low-power synchronous timing motors (such as those for traditional electric clocks) may have multi-pole PM external cup rotors, and use shading coils to provide starting torque.

Telechron clock motors have shaded poles for starting torque, and a two-spoke ring rotor that performs like a discrete two-pole rotor.

This allows the selection of motor starting torque to be closely matched with the driven load requirements.

Starting torque is about 2.5 times full-load torque with twice full-load current.

In two-pole single-phase motors, the torque goes to zero at 100% slip (zero speed), so these require alterations to the stator such as shaded-poles to provide starting torque.

Another reason is starting torque.

The intention was to use this "power wire" additional winding to provide starting torque for induction motors, with the main winding providing power for lighting loads.

It's starting torque will be very high.

Start capacitors briefly increase motor starting torque and allow a motor to be cycled on and off rapidly.