Miniature circuit breakers (MCBs) are fitted in newer consumer units in place of fuses. They automatically cut off the supply of electricity if a circuit is overloaded. They have the advantage that they can be manually reset without having to replace wire as in the case of the traditional fuse. The MCBs have either a button or lever that can be flicked to reset it. They are used instead of fuses due to their convenience and improved safety features.
RCDs (Residual Current Devices) are designed to help prevent electric shock and other accidents due to faulty electrical appliances or wiring. An RCD can detect changes in the proper flow of electric current: when a flex or cable is cut, for instance, or an electrical appliance malfunctions. Within milliseconds of this happening, the RCD automatically disconnects the power supply to the equipment before you can be electrocuted or further damage can be done.
An RCBO is a single device which combines the functions of an MCB (over-current and short-circuit protection) and an RCD (Earth fault protection).
MCBs, RCDs and RCBOs Explained