How many ways does my consumer unit need?

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.

Do consumer units have to be metal?

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.

What is the difference between split load and RCBO boards?

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.

Can I add circuits to my existing consumer unit?

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).

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.

How We Calculate This

Frequently Asked Questions

Last updated: April 2026

All calculations are estimates. Verify with your supplier.

UK Consumer Unit Sizes & Types

Consumer Unit Sizes

Board Configuration Types

Amendment 3 Requirements (BS 7671)

Related Calculators

How We Calculate This

Frequently Asked Questions

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