RCD vs RCBO: What's the Difference?

If you have ever had half the house go dark because one appliance developed a fault, you have met the difference between an RCD and an RCBO first-hand. In short: an RCD protects you against electric shock, but it usually watches over a whole group of circuits at once — so a single fault trips all of them. An RCBO does the same shock protection and the overload protection of a fuse, but on one circuit only — so a fault on the kettle ring no longer takes out your lights, your freezer and your broadband with it.

That one distinction is why almost every modern consumer unit fitted by an electrician in Billericay today is built from RCBOs rather than the older split-load design. Here is what each device actually does, and how to work out what your home needs.

The short version

	RCD	RCBO
What it is	Residual Current Device	Residual Current Breaker with Overcurrent (an RCD and an MCB combined)
What it protects against	Earth leakage — current flowing where it shouldn’t, e.g. through a person. Protects against electric shock and some fire risk	Earth leakage plus overload and short circuit (too much current)
How many circuits it covers	Usually a group of circuits (one or two “split-load” RCDs for the whole board)	One circuit, on its own
When you need it	The 18th Edition requires 30mA RCD protection for most circuits — the question is only how it’s delivered	When you want each circuit protected independently, with the fewest nuisance trips — the modern default
What happens on a fault	Everything on that RCD trips together (e.g. half the house)	Only the faulty circuit trips; the rest of the house stays on
Legal requirement?	30mA RCD protection is required for most circuits under BS 7671. Full RCBOs are the standard modern way to provide it, not a separate legal category	See our transparent pricing guide for what a full-RCBO board involves

First, the third device: the MCB

To understand RCDs and RCBOs you need the humble MCB (Miniature Circuit Breaker) first. An MCB protects a circuit against overload and short circuit — too much current flowing, whether because you’ve plugged in too much or because a live wire has touched a neutral. When that happens the MCB trips and cuts the power before the cable can overheat.

What an MCB does not do is protect you against electric shock. If current leaks to earth — say a damaged cable, or someone touching a live part — an MCB may not see anything wrong, because the total current is still within its limit. That is a completely different kind of fault, and it needs a completely different device.

What an RCD does

An RCD (Residual Current Device) watches for earth leakage. It compares the current flowing out on the live with the current returning on the neutral. In a healthy circuit those match. If some current is escaping to earth — for example through a person who has touched something live — the two no longer balance, and the RCD cuts the power in a fraction of a second. That speed is what makes it a genuine life-saver, and it also reduces certain fire risks from persistent leakage.

The catch is how RCDs were traditionally installed. A common older setup uses one or two split-load RCDs, each covering a whole group of circuits. It protects you perfectly well against shock — but because several circuits sit behind a single RCD, one earth fault anywhere in that group trips the lot. A fault on an outside socket can plunge half your rooms into darkness. That is the classic “why has half the house gone off?” moment, and it is exactly the kind of intermittent problem our fault finding and repair work is designed to trace.

What an RCBO does

An RCBO (Residual Current Breaker with Overcurrent) is the best of both worlds in a single module. It combines the earth-leakage protection of an RCD with the overload and short-circuit protection of an MCB, and it does it on one circuit only.

Because every circuit gets its own RCBO, two things improve at once:

• Full protection on every circuit. Each circuit has both shock protection and overload protection, with nothing sharing or compromising cover.
• Far fewer nuisance trips — better “discrimination”. A fault on one circuit trips only that circuit. Your freezer keeps running while an electrician looks at the faulty socket ring; your lights stay on while the fault is found. In a split-load board, that same fault would have taken out everything on the shared RCD.

This is why a modern consumer unit replacement — sometimes still called a fuse board or fuse box upgrade — is now typically fitted as a full-RCBO board. It satisfies the 18th Edition requirement for 30mA RCD protection on most circuits, and it does so in the way that causes homeowners the least disruption.

The rules behind all this

Two points are worth knowing, both drawn straight from the wiring regulations rather than opinion:

• 30mA RCD protection is required for most circuits under the 18th Edition of BS 7671. Full RCBOs are simply the cleanest, most reliable way to deliver it.
• AFDDs (arc-fault detection devices) are now required on socket circuits in higher-risk residential buildings under Amendment 4:2026. These detect the tell-tale signature of an arcing connection — a loose terminal or damaged cable — that can start a fire before any RCD or MCB would react.

None of this means an older board is automatically unsafe. Plenty of split-load consumer units still do their job. But if yours is being replaced, extended, or flagged on an inspection, RCBOs are the sensible standard to move to.

Which do you need — homeowner, landlord or business?

For most people in Billericay the honest answer is that you are not really choosing between an RCD and an RCBO — you are choosing between an older split-load board and a modern full-RCBO board, because a well-designed new board delivers RCD protection through RCBOs.

• Homeowners: if you are getting frustrated by trips that knock out several rooms at once, or you’re renovating and adding circuits, a full-RCBO board removes most of that nuisance and brings you in line with current standards.
• Landlords: an EICR (electrical safety certificate) is a legal requirement for rented homes, and inspectors will note where RCD protection is missing or where circuits are poorly split. Moving to RCBOs is a common, cost-effective way to close those observations.
• Businesses: independent circuit protection matters even more when downtime costs money — you don’t want a single fault taking a whole area of the premises offline.

If you’re not sure what’s behind your own fuse board, the safest first step is to have it looked at rather than to guess. An electrician can tell you at a glance whether you have MCBs, split-load RCDs or full RCBOs, and whether an upgrade is genuinely worth it for your situation.

Getting it checked

Every home is a little different, so the right answer depends on your existing board, your circuits and what you’re trying to fix. As a NICEIC-registered, Part P approved local team we work to BS 7671, and we’re happy to explain your options in plain English before any work is agreed.

If you’d like to know where you stand — or you’re weighing up a consumer unit upgrade — request a free written quote and we’ll set out exactly what your board needs and what it will cost, with no pressure either way. You can also browse our pricing guide first if you’d rather get a feel for the numbers.