Why are single-phase motors considered not self-starting?

Single-phase motors are classified as not self-starting primarily because they lack the ability to generate sufficient starting torque on their own. Unlike multi-phase motors, which create a rotating magnetic field that facilitates self-starting, single-phase motors operate with a single alternating current supply. This configuration means there is no inherent phase difference to initiate rotation when power is applied.

To overcome this limitation, single-phase motors typically use auxiliary means, such as start windings or external devices, to provide the necessary torque to initiate rotation. These mechanisms create the required phase shift that allows the motor to start and then operate efficiently once it has gained speed.

In contrast, single-phase motors do not rely on gravity or require other complex initiation methods; they simply need additional assistance to overcome the initial inertia. This characteristic distinguishes single-phase motors from other types that can start on their own simply by the nature of their design.