ELECTRIC MOTOR CONTROLS
Once the proper motor is selected, understanding the many various control devices available and
their uses and limitations becomes an important part related to reliable operation and protection of
the motor and the personnel using the motor.
Motor Control Topics
There are four major motor control topics or categories to consider. Each of these has several
subcategories and sometimes the subcategories overlap to some extent. Certain pieces of motor
control equipment can accomplish multiple functions from each of the topics or categories.
The four categories include:
1) Starting the Motor
Across the Line Starting
Reduced Voltage Starting
2) Motor Protection
Other Protection (voltage, phase, etc)
3) Stopping the Motor
4) Motor Operational Control
An understanding of each of these areas is necessary to effectively apply motor control
principles and equipment to effectively operate and protect a motor.
All motors must have a control device to start and stop the motor called a “motor controller”.
A motor controller is the actual device that energizes and de-energizes the circuit to the motor so
that it can start and stop.
Motor controllers may include some or all of the following motor control functions:
starting, stopping, over-current protection, overload protection, reversing, speed
changing, jogging, plugging, sequence control, and pilot light indication.
Controllers range from simple to complex and can provide control for one motor,
groups of motors, or auxiliary equipment such as brakes, clutches, solenoids, heaters,
or other signals.
The starting mechanism that energizes the circuit to an induction motor is called the “starter” and
must supply the motor with sufficient current to provide adequate starting torque under worst case
line voltage and load condi