ACB vs MCCB vs MPCB: choosing low-voltage switchgear

A low-voltage switchboard uses three families of protective device, and specifying the wrong one is a common source of nuisance tripping, poor discrimination and failed inspections. This guide explains what an ACB, an MCCB and an MPCB each do, and where each belongs in a GCC installation.

Air circuit breaker (ACB)

The ACB is the heavyweight of the LV world — a large, often drawable breaker used at the top of the system. It sits on the main incomer, on bus-ties, and on the largest feeders, typically from 630 A up to 6300 A.

Its electronic trip unit is highly adjustable, which makes the ACB the device you coordinate the rest of the system around. Drawable construction also means it can be racked out for maintenance without dismantling the switchboard.

Moulded-case circuit breaker (MCCB)

The MCCB is the workhorse for feeders and sub-distribution. Compact and fixed-mounted, it covers roughly 16 A to 1600 A and protects distribution boards, large final circuits and smaller motor feeders.

Higher-rated MCCBs offer adjustable thermal and magnetic settings; smaller ones are fixed. They are the natural choice anywhere an ACB is oversized and an MPCB is too motor-specific.

Motor protection circuit breaker (MPCB)

Motors need protection an ordinary MCCB does not provide cleanly: a thermal overload tuned to the motor's full-load current, and ideally phase-loss sensing. The MPCB integrates short-circuit protection and an adjustable overload in one device, replacing the MCCB-plus-overload-relay combination on a motor circuit.

Choosing between them

• Main incomer or bus-tie, 630 A and above — ACB
• Feeders and sub-distribution, 16–1600 A — MCCB
• Dedicated motor circuits — MPCB
• Always confirm breaking capacity (Icu/Ics) against the fault level
• Check discrimination so the nearest device trips first

Breaking capacity and discrimination

Two checks decide whether a switchboard is safe and well-behaved. First, every breaker's breaking capacity must exceed the prospective short-circuit current at its point in the system. Second, the trip settings must be coordinated so that a fault is cleared by the device closest to it — not by the incomer, which would drop the whole board. In the GCC, both are routinely checked by the authority having jurisdiction.

How Al Sanaya can help

We supply LV switchgear and protective devices across the GCC and MENA, and our engineering team can specify the breaker schedule, verify breaking capacity against the fault study, and check discrimination before the board is built.