The single-phase auxiliary phase electric motor is the most used these days. Its mechanical construction is identical to that of the three-phase induction motors 0.5 hp 56 motor and in the stator there are two windings: one of thicker wire with large number of turns (main winding) and one of thinner wire with few turns (auxiliary winding).

The main winding is switched on during the entire engine run time, but the auxiliary winding only acts during start-up. This winding is switched off when an automatic device is placed between the part of the engine cover and part of the rotor.

Typically, a capacitor is connected in series with the auxiliary winding, thereby optimizing the starting torque of the motor. The single-phase auxiliary phase motor operates in function of the difference between the inductances of the two windings, since the number of turns and the gauge of the conductors of the main winding are diverse with respect to the winding. The currents circulating in these windings are out of phase with each other and because of the greater inductance in the (main) working winding, the current flowing through it is delayed relative to that which circulates in the starting (auxiliary) winding, which has less inductance.