Miniature Circuit Breakers - MCB
(MCBs) to BS EN 60898 are suitable for operation by ordinary persons and have fixed protection settings, generally a two-position on/off operating handle and performance relative to the final circuits in an electrical installation. They would normally be the final overcurrent protection measure in the electrical system, for example before sockets or lighting circuits.
Typical current ratings are from 0.5 A to 125 A. Short-circuit ratings may be up to 25 kA. Performance and testing is in accordance with BS EN 60898 for domestic and similar applications categorised by the trip characteristic types B, C & D. MCBs may also be available with application-specific tripping characteristics.
MCBs may also be rated in accordance with BS EN 60947-2 for industrial or similar applications.
Moulded Case Circuit Breakers - MCCB
(MCCBs) may have fixed or adjustable protection settings, normally a three-position toggle operating handle giving on-off-tripped indication plus reset function, and a performance level relative to the incoming supply. They can be installed at a point close to the supply transformer.
Typical current ratings are from 16 A to 1600 A though ratings up to 3,200 A are available. Short-circuit ratings may be up to 100 kA. Performance and testing are in accordance with BS EN 60947-2.
Air Circuit Breakers - ACB
(ACBs) are normally used as the main incoming protection and have a spring-operated mechanism to open and close the device often charged by an internal motor. The protection settings will include time delays and the devices will have a short-time withstand value to give full discrimination under fault conditions with downstream protection devices.
Typical current ratings are 630 to 6,300 A. Short-circuit ratings may be up to 150 kA. Performance and testing are in accordance with BS EN 60947-2.
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