Question 1

How many ways does my consumer unit need?

Accepted Answer

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.

Question 2

Do consumer units have to be metal?

Accepted Answer

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.

Question 3

What is the difference between split load and RCBO boards?

Accepted Answer

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.

Question 4

Can I add circuits to my existing consumer unit?

Accepted Answer

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).

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

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

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Amendment 3 Requirements (BS 7671)

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