The auxiliary phase single phase electric motor is the most widely used. Its mechanical part is similar to that of three-phase induction motors. Thus, in the stator there are two windings: one of thicker wire with large number of turns (main winding) and one of narrower wire with few turns (auxiliary winding).
The main winding is switched on for the entire running time of the motor, but the auxiliary winding only acts during start-up. This winding is disconnected when an automatic instrument is located located in the engine cover and part in the rotor. Typically a capacitor is connected in series with the auxiliary winding, thereby improving the motor starting torque.
The single-phase auxiliary phase motor operates as a function of the difference between the inductances of the two windings because of the number of turns and the gauge of the conductors of the main winding are dissimilar to the winding.
The currents circulating in these windings are out of phase with each other. Since the larger inductance in the (main) working winding, the current flowing through it lags in association with that which flows in the starting (auxiliary) winding, whose inductance is lower.