ABSTRACT
Electrical power control systems are used with many types of loads. The most common electrical loads are motors; so our discussion will deal mainly with electric motor control. However, many of the basic control systems are also used to control lighting and heating loads. Generally, the controls for lighting and heating loads are less complex. A “start-safe” switch circuit often contains a key, which the machine operator uses to turn the control circuit on or off. The selector switch is placed in series with the windings of the motor. When the selector is changed from the HIGH position to the LOW position, a modification in the windings of the motor is made. The circuits discussed in this section represent some basic power control functions, such as start-stop, forward-reverse-stop, jogging, and multiple-speed control. Most motor-starting systems utilize one or more magnetic contactors. A schematic diagram of a magnetic contactor circuit used for controlling a single-phase motor.
