If you’ve looked inside a modern fuse box or read an electrician’s quote, you’ll have seen “RCD” and “RCBO” — and they sound almost the same. They’re not. Understanding the difference helps you see why a board full of RCBOs is worth more than a cheaper RCD setup, and why it matters when half your house goes dark.

What each device does

Three terms are worth getting straight:

• MCB (Miniature Circuit Breaker): protects a circuit against overload and short circuit — too much current. It does not protect against electric shock.
• RCD (Residual Current Device): detects earth leakage — current escaping where it shouldn’t, such as through a person — and cuts power in milliseconds. This is the shock protection. An RCD does not protect against overload on its own.
• RCBO (Residual Current Breaker with Overcurrent): combines both — it’s an RCD and an MCB in a single device, protecting one circuit against both earth leakage and overload/short circuit.

The key practical difference: what trips, and how much goes off

This is the part you actually feel in daily life.

• In an RCD-protected board, one or two RCDs typically protect a group of circuits. If there’s an earth fault anywhere in that group, the RCD trips and every circuit on it goes off — potentially half your house, including the freezer and the heating.
• In an RCBO board, each circuit has its own RCBO. A fault on one circuit trips only that circuit — the rest of the house keeps running.

So with RCBOs, a fault in the garden lights doesn’t also kill your fridge and your boiler. That discrimination (or “selectivity”) is the big advantage.

Which is better?

For protection quality and convenience, RCBOs are better — they give per-circuit shock and overload protection and minimise disruption when something faults. The trade-off is cost: a board fully populated with RCBOs is more expensive than the older “split-load” design with a couple of shared RCDs.

That said, the older split-load RCD board is still safe and compliant — it provides the essential shock protection. The choice is often about budget vs convenience rather than safe vs unsafe.

What the regulations expect

Modern installations require RCD protection for most circuits (sockets, circuits in bathrooms, cables buried in walls, and so on). Both a split-load RCD board and a full-RCBO board can meet this — but if your consumer unit has no RCD protection at all (common in older boards with just MCBs or rewireable fuses), that’s a significant safety gap that should be addressed. Our fuse box replacement guide covers upgrading older boards.

“Why does my RCD keep tripping?”

A common frustration with shared-RCD boards: a single faulty appliance anywhere in the group trips the RCD and takes out multiple circuits, leaving you guessing which appliance caused it. Moving to RCBOs makes fault-finding far easier, because the tripped circuit tells you immediately where the problem is. If nuisance tripping is driving you mad, that’s often a strong reason to upgrade.

Which should you choose for an upgrade?

If you’re replacing your consumer unit, RCBOs are usually the better long-term choice — better protection, less disruption, easier fault-finding — and worth the extra cost for most homes. If budget is tight, a modern split-load RCD board is still a big safety improvement over an old fuse box.

GFL Electrical install and upgrade consumer units across East London and will explain the RCD vs RCBO choice in plain terms for your home and budget. See our fuse box replacement service or call 020 3774 5604.