RCBO stands for 'Residual Current Breaker with Over-Current'.

An RCBO is simply an MCB (Miniature Circuit Breaker) and RCD (Residual Current Device) combined into one unit.

If there is a current leakage, the RCBO will rapidly trip the entire circuit.

RCBOs are most commonly used in applications where there is a need to combine protection against overcurrents (a condition that exists in an electrical circuit when the normal load current is exceeded) and protection against earth leakage currents (and electric current that finds its way to earth via an unintended path).