RCD vs RCBO vs MCB — what’s the difference?
An MCB protects a circuit from overload and short-circuit. An RCD protects against earth leakage — the kind of fault that causes electric shock — but usually covers a whole group of circuits at once. An RCBO combines both functions in a single device, per circuit, so a fault only trips that one circuit. Modern consumer units are built around RCBOs.
MCB — overload protection
A Miniature Circuit Breaker (MCB) is the modern replacement for a rewireable fuse. It trips if a circuit draws too much current (overload) or there's a short-circuit, protecting the cable from overheating. It does not protect against electric shock from an earth fault — that's the RCD's job.
RCD — shock protection
A Residual Current Device (RCD) watches for current leaking to earth — for example through a person touching a live part, or a damaged cable — and cuts the power in milliseconds. In older boards a single RCD often covers half the house, which is why a fault on one circuit can take out several others.
RCBO — both, per circuit
An RCBO (Residual Current Breaker with Overcurrent) combines the MCB and the RCD in one device, fitted per circuit. The big advantage is selectivity: a fault on the kitchen circuit trips only the kitchen, leaving the lights, freezer and everything else running. A modern, all-RCBO board is what we install as standard.
Why does one fault take out half my house?
That's the sign of an older board where a single RCD covers a group of circuits. Upgrading to an all-RCBO consumer unit means a fault only trips its own circuit.
Is an MCB enough on its own?
No — an MCB protects the cable from overload but not people from electric shock. Modern installations need RCD protection too, which is why RCBOs (combining both) are the standard.
Do I need to replace my whole board to get RCBOs?
Usually a consumer-unit upgrade is the clean way to move to an all-RCBO board. We'll advise after a look whether that's the right step for your installation.