What is an
RCBO Board?
A homeowner guide to the modern UK consumer unit standard. How an RCBO works, why every circuit gets its own dedicated protection plus how a full RCBO board behaves differently to a split-load board when something faults.
An RCBO board is a UK consumer unit where every circuit has its own dedicated RCBO (Residual Current Breaker with Overcurrent). Each RCBO combines an RCD plus an MCB into a single device. That means each circuit gets its own 30mA earth fault protection alongside its own overload plus short circuit protection. A fault on one circuit only takes that circuit offline. Lights, freezer plus router stay live. RCBO boards are the recommended modern UK domestic standard under BS 7671:2018+A2:2022.
Four figures that
define the design
These figures are baked into every modern RCBO consumer unit fitted under BS 7671 in 2026.
RCBO Density
The defining feature. Every circuit gets its own dedicated RCBO. No shared RCD banks. No grouped protection.
Trip Threshold
The maximum residual current allowed before the RCBO must disconnect its circuit to protect against shock.
Typical Main Switch
Standard UK domestic incoming rating. The main switch sits before the busbar plus the RCBOs.
Edition Standard
RCBO boards are the recommended UK standard under BS 7671:2018+A2:2022. Required on most new build plus rewire installs.
How an RCBO board
is laid out
Open the front cover plus you find a familiar four-part layout. The main switch sits at one end then a row of RCBOs covers the rest of the busbar.
Main Switch
A double-pole 100A isolator at one end of the board. The first device the meter tails reach. Operates the whole installation in one move.
Busbar
A copper strip running across the board carrying power from the main switch to every RCBO. Hidden under the front cover but the spine of the board.
RCBO Per Circuit
Each circuit gets its own RCBO clipped to the busbar. Combined RCD plus MCB on a single device. Dedicated neutral terminal on the body of the device.
Earthing Terminal
The main earthing terminal where the supply earth lands plus where main protective bonding to gas plus water originates. Every CPC traces back here.
An RCBO board treats every circuit as its own protected island
The clue is in the name. RCBO stands for Residual Current Breaker with Overcurrent. It is a single device that does two jobs at once. It detects earth faults to the same 30mA threshold that an RCD does. It also trips on overload plus short circuit to the same standards an MCB does. One device. One circuit. Two functions handled simultaneously.
An RCBO board (sometimes called a high-integrity board or full RCBO consumer unit) is a UK consumer unit where every circuit has its own RCBO. There are no shared RCD banks. There are no plain MCBs sitting underneath an RCD. Every line entering the board terminates at an RCBO. Every neutral lands on a dedicated terminal on the body of that same RCBO. Every circuit is electrically independent of every other circuit.
What this means in practice
The behaviour difference between an RCBO board plus a dual RCD board only becomes obvious when something faults. On a dual RCD board, an earth fault on one circuit drops the whole RCD bank that the circuit sits under. Half the house goes dark. On an RCBO board, the same earth fault only drops the affected circuit. Lights stay on. The freezer keeps running. The router keeps the house online. You troubleshoot one circuit, not five.
Nuisance trips behave the same way. On a dual RCD board, a few appliances each leaking a small amount of current to earth can sum to enough to trip the bank RCD. On an RCBO board, that same leakage is split per circuit. Each RCBO sees only its own circuit's tiny share. Trips become rare plus when they do happen they point straight at the cause.
High-integrity vs full RCBO
You will sometimes hear electricians distinguish between a high-integrity board plus a full RCBO board. These are not always the same thing. A high-integrity board has dual incoming neutrals so RCBOs can be split across two neutral bars. A full RCBO board uses RCBOs on every circuit. In modern installs the two terms often overlap because most full RCBO boards also have high-integrity neutral arrangements. The practical effect for the homeowner is the same: every circuit gets its own dedicated RCD plus MCB protection.
Inside the enclosure, RCBOs come in two width formats:
- 1 module RCBOs (slim) take the same space on the busbar as a standard MCB. This means a 16 way enclosure can hold 16 RCBO-protected circuits without needing a bigger box.
- 2 module RCBOs (wider) are older format devices. They take twice the busbar space which limits how many circuits fit in a given enclosure size.
Why RCBO is now standard
BS 7671 has progressively made it harder to design a domestic installation without RCBO protection. Section 411.3.3 requires additional protection by RCD on most circuits in dwellings. Section 411.3.4 (added in Amendment 2) requires AFDD protection on certain circuits. The cleanest way to meet these requirements without grouped circuits dropping the house is full RCBO. Manufacturers have responded by making RCBO devices cheaper plus making their consumer unit ranges RCBO-ready by default.
RCBO board install
cost ranges
RCBO boards cost a little more on parts than dual RCD because each circuit gets its own combined device. Labour is similar. The lifetime cost is often lower because nuisance call-outs drop sharply.
RCBO Board Cost Bands
Prices include parts, labour, EIC certification plus Building Control notification. Remedial work uncovered during testing is quoted separately.
Four moments that made
RCBO the standard
RCBOs have existed for decades. Their move to default UK domestic standard happened in four broad steps.
17th Edition Adopted
RCD protection required on most domestic circuits. Most installs adopted dual RCD as the cost-efficient response.
Metal Enclosure Mandated
Third amendment to 17th Edition required non-combustible enclosures. Full RCBO arrangements became more common.
18th Edition Published
BS 7671:2018 strengthened requirements around circuit independence, AFDDs plus SPDs. RCBO design fits all three cleanly.
Amendment 2 Plus Slim Modules
Slim 1-module RCBOs become standard. Full RCBO boards are now the default specification on new builds plus rewires.
Four facts about
RCBO boards
One fault, one circuit
The headline benefit. A fault on one circuit only takes that circuit offline. Every other circuit in the house keeps running normally.
Test every RCBO twice a year
Press the test button on every RCBO every 6 months. Each must trip instantly. If any do not trip, contact a registered electrician.
Diagnostics get easier
When something does trip, the RCBO that tripped tells you exactly which circuit faulted. Troubleshooting goes from hours to minutes.
EV plus solar ready
Modern RCBO boards are designed with the spare capacity plus correct RCD types needed for EV chargers, solar PV plus battery storage.
Consumer Unit Upgrades in Milton Keynes
C-Lec Electrical fits full RCBO consumer units to BS 7671 across Milton Keynes, Bedford plus the surrounding Bedfordshire area. Free quote, certified install, EIC plus Building Control notification handled in full.
RCBO board vs
dual RCD board
Both are compliant in 2026. Both pass an EICR. The choice comes down to budget plus how the home behaves when a fault appears.
Modern preferred route
- ●Each circuit has its own combined RCD plus MCB on a single device.
- ●One earth fault only takes the affected circuit offline. Rest of the house stays live.
- ●Far less prone to nuisance trips because each device sees only its own circuit.
- ●Higher parts cost than dual RCD on the install. Lower lifetime call-out cost.
- ●Recommended on new builds, full rewires plus EV charger installs.
Lower cost compliant route
- ●Two 30mA RCDs cover banks of MCBs across the board.
- ●One earth fault drops a whole RCD bank. Half the house goes off at once.
- ●More prone to nuisance trips because cumulative leakage adds up across the bank.
- ●Lower parts cost on the install. Higher likelihood of reactive call-outs.
- ●Compliant on a budget-driven replacement where existing groupings are sound.
For the wider context on consumer unit types, RCDs, AFDDs plus when an upgrade is genuinely needed, head back to our full guide to consumer units where every common homeowner question is answered in one place.
Back to the Consumer Units Guide
This article sits inside our complete Consumer Units knowledge base. The hub covers everything from board types plus RCBOs through to landlord requirements plus BS 7671 wiring regulations.
More on consumer
unit protection
If you have not seen a split-load board broken down before, the explainer on what is a dual RCD board sets out how the older split-load design works plus where RCBO improves on it. To understand the next layer of protection now appearing on modern boards, our explainer on what is an AFDD board covers arc fault detection plus when it is required. For a side-by-side decision guide, our deep dive on RCBO vs dual RCD board covers cost, behaviour plus the right choice for each scenario. If you need a board fitted in Milton Keynes or Bedford, our consumer unit upgrades service page is the fastest route to a quote.