- To provide a means of starting and stopping the motor and, at the same time, of limiting the starting current if required.
- To give adequate protection to the motor under all conditions.
- To allow speed changing when required.
- To provide means of braking the motor when required.
- To reverse the direction of rotation when required.
Protection of the motor must be automatic, but the other operations may be arranged to be under the control of an operator, or may be partly or fully-automatic.