What Is an RCBO? RCD vs RCBO Explained

RCBO is one of those acronyms that shows up on a quote and rarely gets unpacked properly, mostly because it's really two other acronyms combined into one device — RCD and MCB.

Here's what it actually means, and why it's become the standard for modern consumer units.

Breaking down what it combines

RCBO stands for Residual Current Breaker with Overcurrent protection. It combines what an MCB does — protecting against overload and short-circuit current that could cause a fire — with what an RCD does — detecting current leaking to earth that could cause an electric shock. One device, two jobs.

Why this matters compared to an older setup

Older consumer units often used a single shared RCD covering several circuits at once, alongside separate individual MCBs. The problem with that setup is that a fault on any one of those circuits trips the shared RCD, which takes out every circuit connected to it — lights, sockets, and everything else on that side of the board goes off together.

With an RCBO fitted per circuit, a fault on your kitchen sockets trips only the kitchen sockets. The rest of the property, including the lights, stays on. It's a genuinely practical improvement, not just a technical upgrade.

Why not every consumer unit has always used them

Cost is the main reason — RCBOs are individually more expensive than plain MCBs paired with a shared RCD, so older installations, especially in properties fitted out before RCBOs became the practical standard, often used the cheaper shared arrangement instead.

What this means for a consumer unit upgrade

When we upgrade an older board, moving to individual RCBOs per circuit is standard practice now, not an optional extra — it's a meaningfully better setup for very little extra cost once you're already replacing the whole unit.