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UK Consumer Unit Sizes & Types
Consumer unit types from 6-way to 24-way, split load vs dual RCD vs RCBO boards and Amendment 3 metal enclosure requirements.
Consumer Unit Sizes
| Ways | Usable Circuits | Typical Application | Approx. Width (mm) |
|---|---|---|---|
| 6 | 4–6 | Small flat, garage, outbuilding | ~280 |
| 8 | 6–8 | Small house, flat | ~320 |
| 10 | 8–10 | Average 2-3 bed house | ~360 |
| 12 | 10–12 | 3-4 bed house | ~400 |
| 16 | 14–16 | Large house, multiple heating zones | ~480 |
| 20 | 18–20 | Very large house, outbuildings | ~560 |
| 24 | 22–24 | Large property, commercial conversion | ~640 |
Board Configuration Types
| Type | Protection | Cost | Pros / Cons |
|---|---|---|---|
| Split load (single RCD) | 1 RCD + MCBs | Lowest | Cheap but all circuits trip together |
| Dual RCD | 2 RCDs + MCBs | Mid | Half circuits per RCD, less nuisance tripping |
| High integrity | 2 RCDs + RCBOs for critical circuits | Mid-high | Critical circuits on individual RCBOs |
| Full RCBO | Individual RCBO per circuit | Highest | Best protection, no nuisance tripping |
Amendment 3 Requirements (BS 7671)
- Metal (non-combustible) enclosure mandatory for domestic installations since January 2016
- Metal enclosure must be earthed
- Main switch must be at least 100 A for single-phase domestic supply
- All circuits in domestic premises must have 30 mA RCD protection
- Surge protection devices (SPDs) required where the consequence of overvoltage would be serious (18th Edition Amendment 2)
Related Calculators
See the Circuit Breaker Types for MCB/RCD specifications, or the UK Cable Sizes for cable current ratings per circuit. See also the Consumer Unit Sizing Calculator.
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Frequently Asked Questions
Count your circuits plus allow spare ways for future expansion. A typical 3-bed house might have: 2 lighting circuits, 2 ring main circuits, 1 cooker, 1 shower, 1 immersion, 1 outdoor circuit = 8 circuits. A 10-way or 12-way board allows for growth. Larger houses or those with underfloor heating, EV chargers, or outbuildings may need 16-way or 20-way boards.
Yes. Since Amendment 3 to BS 7671 (January 2016), all new or replacement consumer units in domestic premises must be enclosed in a non-combustible material — in practice this means a metal (steel) enclosure. This was introduced to reduce fire risk. The metal enclosure must also be earthed. Plastic consumer units are no longer acceptable for new domestic installations.
A split load board has one or two RCDs protecting groups of circuits — if one RCD trips, all circuits on that group lose power. A full RCBO board has an individual RCBO for every circuit — if one trips, only that circuit is affected. RCBO boards are more expensive but far more convenient. Dual RCD boards are a middle ground, splitting circuits across two RCDs to limit the impact of tripping.
If your consumer unit has spare ways, a qualified electrician can add circuits subject to the board having adequate capacity and the addition being notifiable electrical work under Part P of the Building Regulations. If no spare ways exist, a secondary consumer unit (sub-board) can be added fed from a spare way or a separate switch fuse. Any changes to consumer units are notifiable work requiring Building Control notification or certification by a registered competent person (e.g. NICEIC, NAPIT).
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Last updated: April 2026
Verified against UK standards · estimates only, confirm with your supplier.