Motor Control Centres (MCC) and Starters
A practical guide to Motor Control Centres and the starter types inside them — how each starts and protects an electric motor, and how MCCs centralise control of pumps, fans and HVAC plant in buildings.
A Motor Control Centre (MCC) is an assembly of enclosed sections that house the equipment used to start, stop, protect and control electric motors from one place. Instead of scattering individual starters around a plant room, an MCC brings them together in a single line-up fed from a common busbar, making operation, protection and maintenance far more orderly.
In MEP-heavy buildings the MCC is the muscle behind the mechanical systems: it drives the chilled-water and domestic-water pumps, the ventilation and smoke fans, cooling-tower fans and similar loads. Understanding how a motor is started and protected explains why an MCC is built the way it is and why the right starter choice matters for reliability and energy use.
How it works
The busbar and incomer. Power enters the MCC through an incoming circuit breaker and is distributed along a common busbar that runs the length of the line-up. Each motor feeder taps off this busbar, so the busbar rating and short-circuit withstand define the whole assembly.
The motor feeder (bucket). Each motor has its own compartment, often a withdrawable "bucket". A typical feeder contains a means of isolation, short-circuit protection (a breaker or fuses), a contactor that switches the motor on and off, an overload relay that protects the motor windings, and the control wiring for start/stop and status.
Starting an induction motor. A motor draws a large inrush current at the instant it starts — often several times its running current — because it must overcome inertia and magnetise from standstill. The job of the starter is to make and break this current safely and, where needed, to limit the inrush so it does not disturb the supply or stress the driven equipment.
Starter methods. Direct-on-line (DOL) connects the motor straight to full voltage; simple and robust for small motors. Star-delta starts the windings in star to reduce starting current, then switches to delta to run. A soft starter ramps the voltage up electronically for a smooth start and stop. A variable frequency drive both soft-starts and varies running speed for the best energy performance.
Protection and control. Overload relays protect against sustained over-current that would overheat the windings; short-circuit devices clear faults instantly. Modern MCCs add electronic motor-protection relays and communication so each starter reports current, status and trips to the building management system, allowing remote control and condition monitoring.
Main types
In the UAE
- MCCs and switchgear on connected installations in the UAE must meet IEC-based standards (such as IEC 61439 for assemblies) and the wiring regulations of authorities like ADDC and DEWA.
- Pumps and fans serving life-safety duties — fire pumps, smoke-control and stair-pressurisation fans — must align with the UAE Fire and Life Safety Code, with dedicated, protected supplies and clear control.
- With cooling dominating energy use in the Gulf, VFDs and efficient starters in MCCs are central to meeting Estidama and energy-efficiency targets on pump and fan loads.
How GPR applies this
GPR specifies, installs and commissions Motor Control Centres for HVAC, pumping and ventilation plant across Abu Dhabi, selecting DOL, star-delta, soft-start or VFD feeders to suit each motor and duty. We coordinate MCC ratings and forms of separation with the upstream distribution and protection, integrate starter status and metering into the building management system, and ensure life-safety motor supplies meet UAE Civil Defence requirements.
Frequently asked questions
What is a Motor Control Centre used for?
It houses the starters, protection and control for many electric motors in one assembly fed from a common busbar, typically driving pumps, fans and HVAC plant.
Why do motors need a special starter?
An induction motor draws a large inrush current at start-up; the starter makes and breaks this current safely and can limit it so it does not disturb the supply or stress the equipment.
What is the difference between DOL and star-delta starting?
DOL applies full voltage immediately and is simplest for small motors; star-delta starts in star to reduce the starting current, then switches to delta to run, suiting larger motors.
When should a soft starter or VFD be used instead?
A soft starter gives a smooth ramp for starting and stopping; a VFD does that and also varies running speed, giving the largest energy savings on variable pump and fan loads.
How is a motor protected in an MCC?
An overload relay trips on sustained over-current to protect the windings, while a breaker or fuses clear short circuits instantly; modern MCCs add electronic protection and monitoring.