induction motor

induction motor

Diagram of an induction motor.

An induction motor is an alternating-current electric motor in which the current in the moving part is induced (see electromagnetic induction) rather than supplied via slip-ring contacts. Also called an asynchronous motor, it is the commonest motor in domestic and industrial use.


The coil forming the armature of a simple DC motor is replaced by a 'squirrel cage'. This consists of aluminum or copper bars connecting each end to a ring, the whole embedded in a laminated iron rotor. The field, at least two coils inside the motor body, is shaped to allow the rotor to revolve inside with a small clearance. Flux lines caused by an alternating current passing through the field cut the cage bars, inducing the current – hence the term 'induction' motor.