shading coil

A shading coil is a component in single-phase induction motors that makes them self-starting. These motors have a main winding connected to the power supply and a second, short-circuited winding called a shading coil.12

The shading coil is placed ahead of the main winding in the direction of rotation. It delays the magnetic flux in the area it encircles, creating a small rotating field when the motor is at a standstill. This allows the motor to generate starting torque, though it is typically low. Shaded-pole motors are generally inefficient and used in small power applications where initial cost is more important than energy efficiency, such as in fans and small household appliances.2