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Fuses, MCBs, RCDs, and RCBOs are all devices used to protect users and equipment from fault conditions in an electrical circuit by isolating the electrical supply. With fuses and MCBs only the live feed is isolated; with RCDs and RCBOs both the live and neutral feeds are isolated.
A fuse is a very basic protection device, which is destroyed (i.e. it 'blows') and breaks the circuit should the current exceed the rating of the fuse.
An MCB is a modern alternative to fuses used in Consumer Units (Fuse Boxes). When an overload is detected in the circuit it ‘switches’ off.
RCDs are tripped if they detect a small current imbalance between the Live and Neutral wires above the trip value - this is typically 30mA.
RCBOs combine the functions of a MCB and a RCD in one unit. They are used to protect a particular circuit, instead of having a single RCD for the whole building.
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