MCBs

MCBs, or miniature circuit breakers, are automatically operated electrical switches designed to protect circuits from damage caused by overload or short circuit. Unlike fuses, MCBs can be reset after tripping, making them reusable protective devices in electrical installations. They are commonly installed in distribution boards to guard individual circuits.

MCBs operate as thermal-magnetic devices. A bimetallic strip responds to overload current, bending and triggering a trip, while a magnetic coil provides an instantaneous trip for short circuits. Trip characteristics are often indicated by letters such as B, C, or D, reflecting the multiples of the rated current In at which the device trips. This allows selection for different load profiles and inrush conditions.

Key specifications include the current rating In, typically ranging from about 6 to 63 amperes for standard household types, and the breaking capacity Icn, which defines the maximum fault current the MCB can interrupt safely. Rated voltage is commonly 230/240 V for single-phase systems and higher for three-phase installations. MCBs come in modular form for mounting in consumer units and distribution boards, and in some cases are combined with residual current protection as RCBOs.

Standards and installation practices vary by region. In many parts of the world, IEC 60898-1 and IEC 60947-2 govern MCB design and performance; in North America, UL and other national standards apply. Proper selection considers the load, conductor size, and prospective fault current, and MCBs should be used in coordination with other protective devices.

Safety and maintenance notes: MCBs reduce fire risk by interrupting fault currents but do not protect against electric shock. They are designed for repeated operation and replacement if damaged, with proper labeling and testing during installation and maintenance.