Miniature Circuit Breakers (MCBs) and Molded Case Circuit Breakers (MCCBs) are two of the most commonly used protective devices in Low Voltage Switchgear panels.
Given their importance and extent of usage, it is critical to understand the characteristics and key differentiating factors between the two products.
1- Applicable Standards
MCBs and their relevant parameters are governed by BS EN 60898 standards while MCCBs are governed by the BS EN 60947-2 standards. This results in differences in the definitions of the parameters applicable to the respective devices.
Miniature Circuit Breakers, or MCBs, belong to the family of Modular devices and are used in domestic applications, such as consumer units or Distribution Boards.
Molded Case Circuit Breakers, or MCCBs, are higher rated devices used in industrial and commercial protection applications, featuring in Sub Main Distribution Boards and Main Distribution panels.
3- Operating Range
MCBs are available in a range of breaking capacities usually between 6kA to 25kA and are rated to carry load currents of up to 100A. They are available in one, two and three pole versions.
MCCBs are available in a range of breaking capacities usually between …. to…. and are rated to carry load currents of up to 2500A. They are available in one, two, three and four pole versions.
4- Tripping Characteristics
MCB tripping characteristics (both thermal and magnetic) are not adjustable. They are designated into categories (B,C,D) based on their response to fault currents.
MCCB tripping characteristics (both thermal and magnetic) are adjustable. The trip units are categorized into three broad sets (FTFM, ATFM and Electronic) based on their response to fault currents.
The tripping operation of MCCBs is different to MCBs in that there are three distinct positions of toggle on the device.
Whereas MCBs are either ‘on’ or ‘off’, MCCBs have a central position when they are tripped. As a further safety feature, the colored flags indicating the ‘on’ and ‘off’ states are masked in the tripped state. The breaker can be reset only after it has been set into the fully ‘off’ state.
While both devices are low voltage circuit breakers installed in projects to protect against faults that may arise in the electrical system, they differ significantly in terms of their range of operation, and primary purpose of use.
The choice of device to be installed is based broadly on the factors listed above.
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