Starting

• The starting and stopping of a motor is controlled by a device known as a motor controller. The motor control supplies the motor circuit with sufficient current to provide enough torque, or turning moment, to start the motor.
  
  

Speed Control

• Few devices driven by motors require the maximum design speed of the motor concerned, so some form of adjustable speed control is required. The simplest forms of speed control involve varying the voltage -- and, in the case of alternating current (AC) motors, the frequency -- of the current applied to the motor windings.
  
  

Other Controls

• A short circuit, ground fault or deliberate overloading of a motor can irreparably damage its windings, so motor circuits are typically fitted with controls -- in the form of circuit breakers or fuses -- to prevent overcurrent. Similarly, if reversing the phase (and direction of rotation) of an alternating current (AC) motor is dangerous, a control is fitted to interrupt the current if this is attempted.