What is a motor control centre (MCC)?

Inside, a motor control centre is divided into sections, each a full-height column holding one or more functional units. A functional unit is everything that forms one complete incoming or outgoing circuit, from the switching device to the cable terminals, but not its connections to the busbars.^[10]

The devices in those units include moulded-case circuit breakers, integrated motor starters and variable speed drives. A 2011 UK manufacturers' association guide notes that they increasingly come in their own integral housing, and that the standard recognises that housing as a means of separation.^[10]

Where continuity of supply matters most, the same guide advises withdrawable or removable functional units, so that a unit can be replaced or added while the busbars and neighbouring circuits stay energised. How the operator is protected while a unit is out is agreed with the maker.^[10]

As a whole, a motor control centre is a power switchgear and controlgear assembly (PSC-assembly). The 2011 guide quotes the standard's definition of that class, a low-voltage assembly "used to distribute and control energy for all types of loads, intended for industrial, commercial and similar applications where operation by ordinary persons is not intended", and names motor control centres among them.^[10]

In South Africa, the standard for a motor control centre is SANS 61439-2:2021 (edition 3), which defines the specific requirements for power switchgear and controlgear assemblies. The SABS lists it as related to IEC 61439-2 and for use with SANS 61439-1:2020 (edition 3), which "lays down the general definitions and service conditions, construction requirements, technical characteristics and verification requirements" for low-voltage assemblies. SANS 61439-2 was approved on 31 May 2021 and reaffirmed on 16 July 2026.^[1][2]

SATS 63107:2021, an SABS technical specification, states that both are identical adoptions of IEC 61439-1 and IEC 61439-2. According to the IEC's record, IEC 61439-2:2020 covers assemblies rated at no more than 1,000 V a.c. or 1,500 V d.c., stationary or movable, with or without an enclosure, including assemblies for the control of equipment consuming electrical energy.^[5][6]

In its summary of the changes in the 2020 edition, the IEC says that edition clarified the forms of internal separation and added a rule: above Form 1, every part in a functional unit's compartment that stays live when the unit is switched off must be protected to at least IPXXB.^[6]

Two SABS documents help the buyer. SATR 61439-0:2023 "identifies, from the user's perspective, those functions and characteristics that should be defined when specifying assemblies", and SATS 63107 sets requirements for integrating and testing internal arc-fault mitigation systems in PSC-assemblies.^[4][5]

On site, SANS 10142-1, the wiring code incorporated into the Electrical Installation Regulations by GN R.243, applies to the electrical installations of industrial premises, among others. Regulation 5(2) allows only components that comply with the standards that code refers to, with proof on the component or certification from its manufacturer or supplier.^[7][8][9]

The form is agreed between the assembly maker and the user, from Form 1 to Form 4. This table follows the UK manufacturers' association guide of July 2011, written to BS EN 61439-2 as it stood then, before the 2020 edition clarified the forms. In forms 2 and 3, sub-form b also separates the cable terminals from the busbars.^[10][6]

Sources:^[10]

The specification should state the form of separation, and in practice the form follows from the tasks to be done with parts live. The guide asks the specifier to weigh what work is needed without isolating the assembly, which tools will be used and the skill of the people doing it, and warns that a form number does not by itself make live working safe: that needs a risk assessment for each situation.^[10]

Higher forms make the assembly larger, more complex and dearer, so the guide's advice is to specify the lowest form that meets the application's needs.^[10]

Ratings belong in the specification too. One South African maker reported in 2015 that its low-voltage products, which include withdrawable MCCs, were type-tested to IEC 61439-1 and IEC 61641 at a maximum test rating of 690 V +5% and 65 kA.^[11]

A request or tender for a motor control centre can state:^[4][10]

• each outgoing circuit: the motor or load it feeds and the device in its unit, such as a motor starter, a variable speed drive or a circuit breaker;^[10]
• the form of separation, and the tasks to be done while adjacent circuits stay live;^[10]
• fixed or withdrawable functional units, and whether units must be replaced or added with the busbars energised;^[10]
• the rated voltage, the short-circuit and internal arc test ratings with the standards they were tested to, and any internal arc-fault mitigation system, which SATS 63107 covers;^[11][5]
• conformity with SANS 61439-1 and SANS 61439-2, and the proof of compliance or certification from the maker or supplier that regulation 5(2) of the Electrical Installation Regulations requires for components;^[1][2][9]
• who connects it and issues the Certificate of Compliance for that work: for a three-phase installation, an industrial electrician registered as an installation electrician or a master installation electrician.^[9]