Motor control center

Lore & Background

Motor control centers have been used since 1950 by the automobile manufacturing industry, which relied on large numbers of electric motors. Today they are employed in many industrial and commercial applications. In environments with very dusty or corrosive processes, the MCC may be installed in a separate air-conditioned room, but often it is placed on the factory floor adjacent to the machinery it controls.

An MCC consists of one or more vertical metal cabinet sections with a power bus and provision for plug-in mounting of individual motor controllers. Very large controllers may be bolted in place, while smaller controllers can be unplugged for testing or maintenance. Each motor controller contains a contactor or solid-state motor controller, overload relays, fuses or a circuit breaker, and a disconnecting switch. Three-phase power enters through separable connectors, and the motor is wired to terminals in the controller.

Motor control centers are typically found in large commercial or industrial buildings where many electric motors need centralized control, such as in a mechanical room or electrical room. They usually sit on floors that often require a fire-resistance rating, and firestops may be needed for cables penetrating fire-rated floors and walls.

Reader's Guide

Motor control centers are significant because they centralize the control and protection of multiple electric motors in large commercial and industrial settings. By grouping motor starters, disconnects, and protective devices in a common enclosure with a shared power bus, MCCs simplify wiring, reduce installation costs, and improve safety and maintenance access. They allow for plug-in mounting of smaller controllers, enabling quick replacement or servicing without disrupting the entire system. The inclusion of options such as variable-frequency drives, programmable logic controllers, and metering equipment makes MCCs adaptable to complex automation and monitoring needs. Their use since 1950 in automobile manufacturing demonstrates their long-standing role in industries requiring coordinated motor control. The availability of both low-voltage (220V to 600V) and medium-voltage (2300V to 15000V) versions extends their applicability to a wide range of motor sizes. The legacy of the MCC is its enduring function as a standardized, scalable solution for managing motor-driven processes in demanding environments.

Did You Know?

• MCCs are typically used for low voltage three-phase AC motors from 220V to 600V, and medium-voltage units for motors from 2300V to 15000V.
• Each motor controller in an MCC can be specified with options such as separate control transformers, pilot lamps, and various overload protection relays.