Among the main functions of the control of an electric motor are starting, direction of rotation, stop, speed regulation, starting current limitation, mechanical protection and electrical protection, among others. An engine only starts spinning at the moment of loading to be due, when stopped, is less than its starting torque.
In some specific applications there is a need for a rapid deceleration of the engine and the load. When turned off the power line motor uses a rotation reversing device with the engine still running. Switching off the mains motor or stopping is done by means of a device, thus preventing it from starting in the opposite direction. In the case of synchronous motors dynamic braking is counted.
Most motors, except single-phase motors such as shaded pole and repulsion, can be used in both directions of rotation, varying only from a specific control.
Alternating current motors, with the exception of universal motors, are constant speed machines. However, it is possible to re-connect the stator coils of an induction motor so that it doubles the number of poles.