Page "Shaded-pole synchronous motor" Paragraph 7

Even by the standards of shaded pole motors, the power output of these motors is usually very low.

Because there is often no explicit starting mechanism, the rotor of a motor operating from a constant frequency mains supply must be very light so that it is capable of reaching running speed within one cycle of the mains frequency.

Alternatively, the rotor may be provided with a squirrel cage, so that the motor starts like an induction motor, once the rotor is pulled into synchronism with its magnet, the squirrel cage has no current induced in it and so plays no further part in the operation.