Abstract: An apparatus and method for controlling a motor used for rotating a drill stem is disclosed. Silicon control rectifier based system regulates the power to the motor. A control unit coupled to the SCR regulator and the motor monitors the motor input current, voltage and speed levels. If during operation the motor current exceeds a predetermined value and at the same time the motor voltage or speed falls below a predetermined value, the control unit activates an alarm condition and causes the SCR regulator to controllably ramp down the current supply to the motor and then reduces the motor speed reference.