In a single phase motors, there is only one main winding and a single phase supply. So these is no rotating magnetic field generated inside the stator of such machine. So such machines are not inherently self starting. The auxiliary winding or starting winding is connected to the ac mains via a capacitor in order to generate a two-phase supply, which can generate EMF when the coils are placed 90° with respect to main winding. This EMF is responsible for the operation of single phase induction motors, adding the capacitor makes the motor self starting.