Specifications

53
NEMA Motor IEC Motor
Motor Control Wherever motors are used, they must be controlled. The most
basic type of AC motor control involves turning the motor on
and off. This is often accomplished by using a motor starter
made up of a contactor and an overload relay. In the example
shown in the following illustration, the contactor closes its
main contacts and starts the motor when the Start pushbutton
is pressed. When the Stop pushbutton is pressed, the contactor
opens its contacts and stops the motor. The overload relay
protects the motor by disconnecting power to the motor when
an overload condition exists. Although the overload relay
provides protection from overloads, it does not provide short-
circuit protection for the wiring providing power to the motor.
For this reason, and because a manual means for disconnecting
power is needed near the motor, a circuit breaker used. A safety
switch can also be used instead of a circuit breaker.
150A
OFF
O
I
ON
Type/Tipo
NDG
Frame DG
Contactor
Overload
Relay
Motor Starter
Stop
Pushbutton
Start
Pushbutton
Circuit Breaker
AC Motor
L1
L2
L3
M
M
M
OL
OL
OL
OL
M
Ma
Auxiliary
(Holding)
Contact
Overload
Contact
Starter
Coil
Motor Control Centers When only a few geographically dispersed AC motors are used,
the circuit protection and control components associated with a
motor are often installed in an enclosure near each motor. When
a larger number of motors are used, these components are
frequently concentrated in a motor control center (MCC).