RCBO
Combines an RCD and a circuit breaker in one device — earth-leakage plus overload/short-circuit protection.
What it is
An RCBO is a single device that does two jobs: it provides earth-leakage protection (like an RCD) and overcurrent protection (like a circuit breaker) for one circuit.
How it works
It contains both an earth-leakage sensing element and thermal/magnetic overcurrent elements. Either an earth-leakage fault or an overload/short can trip it.
Because one RCBO protects a single circuit, a fault on that circuit only trips that circuit — unlike a single RCD protecting many circuits, where one fault takes them all out.
Where it's used
Increasingly the default in modern boards — one RCBO per circuit gives both protections and limits the impact of a fault to one circuit. Telling whether an RCBO tripped on leakage or overcurrent is the key diagnostic step.
Safety first
Never bypass an RCBO's earth-leakage function. Identify whether it tripped on leakage or overcurrent — the fix differs.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Related faults
RCBO tripping — telling overload from earth leakage
An RCBO (combined RCD + MCB) keeps tripping and you need to know whether it's tripping on overcurrent/overload or on earth leakage — the fix is very different for each.
RCD / RCBO keeps tripping
An RCD or RCBO trips repeatedly — immediately on reset, randomly during the day, or only when certain equipment runs. The earth-leakage protection is doing its job; something is leaking.
A circuit breaker keeps tripping (domestic)
One circuit breaker keeps tripping — instantly on reset or after a load runs — and you need to tell an overload from a short or a faulty appliance.
Related definitions
RCD (safety switch)
Detects earth leakage and disconnects fast to protect people from electric shock.
Circuit breaker (MCB)
Automatically disconnects a circuit on overload or short circuit, and can be reset rather than replaced.
Earthing & bonding
Connecting exposed metal to earth so a fault blows protection fast and metalwork can't become live.