MCCs for Controlled, Protected, Monitored Motor Loads

A motor control centre groups the starters, protection and control for multiple motor loads into a single, organised assembly. This centralisation simplifies operation, improves safety and makes maintenance more predictable in industrial and infrastructure facilities. Instead of scattered local starters that are hard to find and harder to document, operators have one well-documented assembly where every motor circuit is labelled, protected and monitored, and where isolation for maintenance is clear and safe.

Exa Power builds both fixed and withdrawable MCCs on authorized ABB systems, including MNS-style platforms where withdrawable functional units are required. Every MCC is engineered and verified to IEC 61439, with starter types selected to match each motor’s duty, starting characteristics and the demands of the driven load.

The choice between fixed and withdrawable construction usually comes down to availability. Withdrawable units allow a faulty starter to be swapped for a spare in minutes without isolating the whole board, which suits continuous processes; fixed construction is robust and economical where short planned outages are acceptable.

Selecting the starting method for each motor is one of the most consequential design decisions in an MCC, because it affects the motor, the driven load, the supply and the running cost. Direct-on-line starting is simple and robust but draws a high inrush, which is acceptable for smaller motors but can disturb the supply for larger ones. Star-delta reduces the starting current for motors that can start unloaded or lightly loaded. Soft starters give a controlled, smooth ramp that limits mechanical and electrical stress, protecting belts, couplings and pumped systems from the shock of a hard start.

Variable frequency drives go further, controlling speed continuously to match the process demand, which can yield significant energy savings on variable-torque loads such as pumps and fans while also providing a smooth start. We match the method to each motor’s rating, the behaviour of its driven load and the characteristics of the supply, so the MCC starts cleanly, runs efficiently and protects the equipment connected to it.

Each motor feeder needs protection that distinguishes between a healthy start and a genuine fault. Starting currents are several times the running current, so overload and short-circuit protection must be coordinated to ride through normal starts while still clearing faults quickly. We select and set thermal overload relays, motor-protection devices and short-circuit protection from coordinated ABB ranges so that protection is selective and the right device operates for the right event.

Type-2 coordination is available where the specification calls for it, limiting damage to the starter under short-circuit so the assembly can be returned to service quickly. For larger or critical motors, electronic motor-protection relays add functions such as thermal modelling, stall and phase-loss protection, and communications to the plant control system.

Withdrawable construction reinforces this by allowing rapid replacement of a functional unit, so a protective operation that takes a motor offline does not have to mean an extended outage for the rest of the plant.