432 Electrical Power Systems Technology
Figure 16-9 shows a circuit that is another method of forward-re-
verse-stop control. This control circuit has the added feature of a high- and
low-speed selector switch for either the forward or reverse direction. 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.
There are many other pushbutton combinations that can be used
with control relays to accomplish motor control, or control of other types
of loads. The circuits discussed in this section represent some basic power
control functions, such as start-stop, forward-reverse-stop, jogging, and
multiple-speed control.
MOTOR-STARTING SYSTEMS
The equipment used with motor-starting systems was studied in
Chapter 15. Some specific systems used for starting electric motors are
discussed in this section.
Function of Magnetic Contactors
Most motor-starting systems utilize one or more magnetic contac-
tors. A schematic diagram of a magnetic contactor circuit used for control-
Figure 16-9. Pushbutton control circuit with a high- and low-speed selector
switch