A shaded-pole motor is an electric motor classified as an asynchronous motor. Like these, it also has an induction (squirrel-cage) motor, in which through a rotating field produced by the stator a torque is created.

However, unlike the asynchronous motors fed with three-phase current, the shaded-pole motor runs on single-phase alternating current.

Since the minimum of two phase-offset voltages are necessary for generating a rotating field, a second “split phase“ must be generated: the field generated by the stator winding is fed into separate pole pieces, round which parts are sited in the direction of rotation (shaded poles) short circuit rings of thick copper material. The magnetic alternating field is subjected here to a time delay caused by the short-circuit rings and thus to a phase displacement relative to that in the main pole.

The rotating field thus generated is adequate to move the rotor, but it is also admittedly load-dependent, and this leads to a lower starting torque than that of three-phase motors. Because of the resistive losses in the short-circuit windings, the operating efficiency of a split-pole motor compared with that of a three-phase asynchronous motor or of a induction motor of similar power is substantially inferior.

Shaded-pole motors are less expensive than three-phase motors or capacitor motors. They have only one winding and have no expensive (and possibly unreliable) capacitor, and are consequently robust and long-lasting. 

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