Basics of Motor Control Centers – SIEMENS

Basics of Motor Control Centers - SIEMENS (on photo: New Motor Control Center and power distribution board up to 7000 amperes)

Motor control

Power distribution systems used in large commercial and industrial applications can be complex.Power may be distributed through:

1. Switchgear,
2. Switchboards,
3. Transformers, and
4. Panelboards.

Power distributed throughout a commercial or industrial application is used for a variety of applications such as heating, cooling, lighting, and motor-driven machinery.

Basic Motor Control

Wherever motors are used, they must be controlled.

Basic motor control

In Basics of Control Components you learned how various control products are used to control the operation of motors.

• The most basic type of AC motor control, for example, involves turning the motor on and off. This is often accomplished using a motor starter made up of a contactor and an overload relay.

The contactor’s contacts are closed to start the motor and opened to stop the motor. This is accomplished electromechanically using start and stop pushbuttons or other pilot devices wired to control the contactor.

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 supplying power to the motor. For this reason, a circuit breaker or fuses are also used.

Typically one motor starter controls one motor. When only a few geographically dispersed AC motors are used, the circuit protection and control components may be located in a panel near the motor.

Motor Control Centers (MCC)

In many commercial and industrial applications, quite a few electric motors are required, and it is often desirable to control some or all of the motors from a central location. The apparatus designed for this function is the motor control center (MCC).

• Motor control centers are simply physical groupings of combination starters in one assembly.

A combination starter is a single enclosure containing the motor starter, fuses or circuit breaker, and a device for disconnecting power.

Other devices associated with the motor, such as pushbuttons and indicator lights may also be included.