What is Controlgear?

By David Humphrey

Industry Trends

Controlgear is a collective term for electrical disconnect switches, fuses, and circuit breakers used to control, protect and isolate electrical equipment.  The term is part of the IEC definition of “switchgear and controlgear”.  Low, medium and high voltage switchgear is used in power distribution applications, while low and medium voltage controlgear is used in industrial applications to control and protect equipment, especially electric motors, from surges, earth faults and short circuits, and to provide basic control functions such as start/stop and ramp up to speed.

Low and medium voltage controlgear is used frequently in motor control centers (MCC). However, MCCs are large, custom-designed systems that include additional components such as branch feeder devices, variable frequency drives, programmable logic controllers, AC drives, and meters.  Also, MCCs are sold as complete solutions with all components pre-installed and wired in electrical cabinets.

Controlgear provides electrical protection for both equipment and persons in several different cases.  Electrical devices such as motors are protected against cases of sudden current overloads that could damage or destroy equipment.  In addition, controlgear protects against short circuits caused by the failure of insulation or mechanical failures.  Finally, controlgear protects electric motors against abnormal conditions such as overcurrent or overheating.

Controlgear in Motor Control Center

Typical Controlgear Components


3- and 4-pole contactors up to 55kW used for switching motors (AC-3 and AC-4) and other high power loads (mainly AC-1); combinations of 2 or 3 contactors for reverse/star delta star); Includes IEC contactors and NEMA rated IEC contactors.

3- and 4-pole AC contactors over 55kW and up to 820A (AC-3) and 1000A (AC-1) used for switching motors (AC-3 and AC-4) and other high power loads (mainly AC-1); 1- and 2-pole DC contactors up to 400A (DC-1/5) and 1000V; Includes IEC contactors and NEMA related IEC contactors.

Contactor Relays

4-pole to 10-pole contactor relays based on 3-phase AC motor contactors for switching of auxiliary circuits (AC-15, AC-14, DC-13)

Overload Relays

3-phase AC thermal and electronic overload relays up to 800 A for protection against overload mainly for motors (based on thermal motor model).

Solid State Relays

1- to 3-pole AC solid state relays and contactors; heavy-duty solid state relay, used for switching electric heaters, small electric motors and lighting loads; max. 100A (AC-1).

Motor Starter Protectors (MSP)

3-phase AC circuit breakers mainly for motor start protection up to 100A against short circuit and overload.

Motor Management Systems

Multifunctional, electronic motor protection in most cases with communication interface; motor protection and control functions; typically communicates operational, diagnostic and statistical data.

Centralized Motor Starters

Combination of MSP and contactor with connector module (direct and reversing starters); combinations of contactor with overload relay; all for use in cabinets (IP20). Typically sold as complete unit; may have communication interface.

Decentralized Motor Starters

Motor starters for decentralized automation periphery; enclosed motor starter protectors for manual starting; may have communication interface.

Soft Starters

AC soft starters up to 1250A for starting of motors with reduced voltage and torque during ramp; after ramp up fixed speed with or without communication interface, with or without bypass; with 3-phase and 2-phase operation.

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