The short answer
A high-integrity consumer unit is a split-load distribution board that contains two RCDs, each covering approximately half of the installed circuits, with the circuits divided between the two groups so that an RCD trip isolates only half the installation rather than the whole of it. The term 'high integrity' reflects the design intent: the split arrangement means that if one RCD trips on an earth fault, the other half of the board stays on, maintaining supply to lights, fridge, router and other circuits in the unaffected group. This was the approach required under the 17th Edition of BS 7671 and remains a compliant option under the 18th Edition for domestic consumer units. A high-integrity dual-RCD board costs less than a full RCBO board but provides less granular fault isolation — a fault trips half the house rather than a single circuit.
The phrase 'high integrity' appears on many consumer units and causes confusion. It is not a superior or premium specification in any absolute sense — it is a description of the dual-RCD split-load arrangement that became standard under the 17th Edition of BS 7671, to address the problem of whole-installation trips caused by older single-RCD boards.
High-integrity consumer unit facts
- Also calledSplit-load board, dual-RCD board
- ContainsTwo RCDs, each covering half the circuits
- Trip impactHalf the installation trips on an earth fault
- Versus RCBO boardLess granular — half-board vs single circuit
- BS 7671 statusCompliant option under 18th Edition
- Typical costLower than a full RCBO board
Why the split-load design was introduced
Earlier consumer units — those with a single RCD incomer or main switch RCD — provided residual-current protection across the whole installation from one device. This meant that any earth fault, anywhere in the house, would trip the entire board. In a family home, finding a faulty appliance in the dark after a complete loss of power was inconvenient and could be genuinely difficult, particularly if the fault was intermittent.
The 17th Edition of BS 7671 (2008) addressed this by requiring consumer units to be designed so that a fault does not result in the loss of the whole installation. The preferred method was to divide the circuits between two RCDs, so that a fault trips only the section it is in. This is the dual-RCD or split-load arrangement, and the term 'high integrity' was used in product literature to describe it. It became the standard domestic board design from around 2008 onwards.
High-integrity dual-RCD versus full RCBO board
The dual-RCD board is often compared with a full RCBO board, and understanding the difference is useful when choosing between them:
- Dual-RCD (high-integrity): two RCDs, each covering multiple circuits. A fault on any circuit behind one RCD trips that RCD and everything behind it. To find the faulty circuit, you turn off all MCBs in that section, reset the RCD, then restore MCBs one at a time until the RCD trips again — telling you which circuit caused it. Meanwhile, the other half of the house has power.
- Full RCBO board: each circuit has its own RCBO. A fault trips only that circuit's RCBO. You can see immediately which circuit tripped (its RCBO will be in the off position) and investigate just that circuit without affecting anything else.
The full RCBO board provides more granular isolation and is the approach preferred by BS 7671 18th Edition. It costs more because each RCBO is more expensive than a plain MCB. The dual-RCD board is a compliant and practical solution and remains widely installed.
| Feature | Dual-RCD (high-integrity) | Full RCBO board |
|---|---|---|
| Devices per circuit | MCB + shared RCD | RCBO (one device per circuit) |
| Earth fault trip impact | Half the board trips | Single circuit trips |
| Fault identification | MCBs switched off one by one | Tripped RCBO visible immediately |
| Relative cost | Lower | Higher |
| BS 7671 18th Edition | Compliant | Preferred option |
Comparison of dual-RCD and full RCBO consumer unit arrangements. Source: BS 7671:2018+A2:2022.
When a high-integrity board is the right choice
A high-integrity dual-RCD board is a sound, compliant choice for most domestic installations where the higher cost of a full RCBO board is not justified. Consider the following:
- If your home has 10 or fewer circuits and the inconvenience of a half-board trip is acceptable, a dual-RCD board is perfectly adequate.
- If you have circuits where continuity matters — a medical device, a sump pump, a fish tank with an aerator — spreading those circuits across both RCDs ensures that an unrelated fault elsewhere does not cut power to all of them simultaneously.
- If cost is the primary consideration and your home has straightforward circuits without unusual continuity requirements, the dual-RCD board is a reasonable choice.
Conversely, if your installation is large, complex, or includes equipment where even a partial outage is disruptive, the RCBO option's per-circuit isolation is worth the additional cost. Your electrician should be able to give you the price difference for your specific installation so you can make an informed choice.
Frequently asked questions
Is a high-integrity consumer unit the same as a dual-RCD board?
Yes — 'high-integrity' is the marketing and product term for a split-load consumer unit that uses two RCDs, each covering half the circuits. The design was standardised under the 17th Edition of BS 7671 to prevent whole-installation trips.
Which is better — a dual-RCD board or a full RCBO board?
In terms of fault isolation, a full RCBO board is better — a fault trips one circuit rather than half the board, and the faulty circuit is immediately identifiable. Whether that benefit justifies the extra cost depends on your installation and how disruptive a half-board trip would be. Both arrangements are compliant with BS 7671 18th Edition.
Why are circuits split across two RCDs on a high-integrity board?
To limit the impact of an earth-fault trip. If all circuits sat behind one RCD, any earth fault would trip the whole installation. Splitting them means a fault on one side leaves the other side running — you can still have lights and some power while you investigate the cause on the affected section.
Sources & further reading
- IET — BS 7671:2018+A2:2022 (18th Edition Wiring Regulations)
- Electrical Safety First — replacing a consumer unit best practice guide
- NICEIC — consumer unit guidance
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property and installation. They are guidance, not a quotation.