UK standard · Consumer unit

Consumer unit diagram: ways, RCBOs and the circuit schedule

The consumer unit is where a floor plan full of socket outlets turns into a finite list of circuits. Getting the board right — enough ways, the right protection arrangement, a schedule that says what each way does — is what makes an installation maintainable ten years later.

Reading time: 9 min·Updated: September 2026·By Planelico

What a consumer unit diagram is

A consumer unit diagram shows what sits inside the board and what each device feeds. It is a different drawing from the floor plan: the plan says where things are, the board diagram says how they are supplied and protected. A complete set of documents for a domestic job usually has both, plus the circuit schedule that ties them together.

If you only ever produce one of the two, produce the floor plan. But a board diagram is what stops two electricians quoting for two different installations — one assuming a ten-way board, the other an eighteen-way one.

What is inside the board

Main switch

A double-pole isolator for the whole board. Domestic boards are commonly 100 A, matching the supply cut-out fuse.

Protective devices

One per final circuit: an MCB, or an RCBO where the circuit needs its own residual-current protection.

RCDs

On a split-load board, two 30 mA RCDs each cover a group of circuits. A full RCBO board does away with them.

Surge protection (SPD)

Since Amendment 2, the default for dwellings unless a documented risk assessment concludes otherwise. It takes up ways.

Neutral and earth bars

Where the circuit conductors terminate. On a split-load board each RCD has its own neutral bar — a classic source of nuisance tripping when they get crossed.

Spare ways

Empty positions left for later. Worth planning in deliberately rather than discovering you have none.

Domestic consumer units must be in a non-combustible enclosure — in practice, metal. If you are looking at a plastic board, it predates that requirement and is worth flagging when you get the installation inspected.

Split-load or full RCBO

This is the main decision, and it has real consequences for how the house behaves when something goes wrong.

	Split-load (dual RCD)	Full RCBO
Cost of the board	Lower	Higher, typically by a few hundred pounds
Effect of an earth fault	Everything on that RCD trips — often half the house	Only the faulty circuit trips
Fault-finding	Split the circuits and retest to isolate the cause	The tripped device names the circuit
Freezer or alarm on its own	Needs a dedicated arrangement to avoid a nuisance trip	Inherently separate
Neutral bar mistakes	Possible — neutrals crossed between RCD groups	Not applicable
Usual choice for	Like-for-like board replacement on a budget	Rewires, extensions and new builds

How many ways do you need?

Count the final circuits your layout actually requires, then add what the board itself consumes and a genuine allowance for the future. A three-bedroom house with an electric shower and a cooker typically needs lighting circuits per floor, socket circuits per floor, a kitchen circuit, the shower, the cooker, and often an immersion heater — before anyone mentions an EV charger or a garden office.

Spare ways are cheap at installation and expensive afterwards. Adding a circuit to a full board means a new board, which means recertifying everything connected to it.

A reasonable rule of thumb: size the board so that a quarter of its ways are still free the day the installation is signed off.

The circuit schedule

The schedule is the list of ways and what each one does. At design stage it records your intent; at certification it is completed by the electrician with the device details and the measured test results, and forms part of the Electrical Installation Certificate.

A design-stage schedule for the house described above might look like this:

Way	Circuit description	Protective device	Cable
1	Lighting — ground floor	6 A RCBO	1.5 mm² T&E
2	Lighting — first floor	6 A RCBO	1.5 mm² T&E
3	Sockets — ground floor ring	32 A RCBO	2.5 mm² T&E
4	Sockets — first floor ring	32 A RCBO	2.5 mm² T&E
5	Kitchen radial	20 A RCBO	2.5 mm² T&E
6	Cooker	32 A RCBO	6 mm² T&E
7	Electric shower	40 A RCBO	10 mm² T&E
8	Immersion heater	16 A RCBO	2.5 mm² T&E
9	EV charge point	32 A RCBO	6 mm² T&E
10	Spare	—	—

An illustration, not a specification. Device ratings and cable sizes have to be calculated for the real installation — its loads, cable routes, grouping and disconnection times.

Generating the board from your floor plan

Working the circuit list out by hand from a plan is tedious and easy to get wrong. Planelico derives it: once the accessories are placed and the rooms are qualified, it proposes the circuit split, the protection distribution and a modular board layout with spare capacity.

1
Place the accessories on the plan
Socket outlets, lighting points, switches, appliance supplies — everything that will eventually hang off a way in the board.
2
Qualify each room
Telling Planelico that a room is a kitchen, a bathroom or a bedroom is what lets it reason about dedicated circuits and constraints.
3
Let Planelico group the circuits
It groups nearby accessories into final circuits, keeps appliances that need their own supply separate, and distributes the result across 30 mA protection.
4
Review and adjust
Rename circuits, move an accessory to another way, force a dedicated circuit. The generated split is a starting point, not a verdict.
5
Export the board layout and schedule
A modular row layout with spare capacity, plus the circuit schedule, exported alongside the annotated plan in one PDF.

See also the BS 7671 electrical plan guide, the guide to generating a panel from a floor plan, and the single-line diagram guide.

Frequently asked questions

What is the difference between a consumer unit and a fuse box?

They do the same job at different ages. "Fuse box" usually means an older board with rewirable fuses and no RCD protection; a modern consumer unit uses MCBs or RCBOs, has 30 mA residual-current protection, and since the 2016 requirement must have a non-combustible — in practice metal — enclosure in domestic premises.

How many ways should a consumer unit have?

Count your final circuits, add the ways taken by the main switch arrangement and any SPD, then leave genuine spare capacity. A typical three-bedroom house lands somewhere around ten to twelve circuits, so a board in the 16-to-18-way range leaves room for a future EV charger, a garden supply or a loft conversion without a board change.

Is a full RCBO board worth the extra cost?

It usually is on a rewire or a new build. With one RCBO per circuit, a fault takes out that circuit alone instead of half the house, and fault-finding becomes much quicker. On a like-for-like board swap in an existing property the economics are closer, and a split-load board may still be a reasonable choice.

Can I replace a consumer unit myself?

No. In England and Wales replacing a consumer unit is notifiable work under Part P, and it requires testing and certification of every circuit connected to it. It has to be done by a registered competent person or notified to building control beforehand.

Does Planelico produce a certified circuit schedule?

No, and no software should claim to. Planelico produces the design intent — the circuits, their grouping and the proposed board layout — in a form your electrician can review and price. The certified schedule is completed on installation, with the measured test results, by the person signing the certificate.

Get the circuit list out of your floor plan

Place your accessories, qualify the rooms, and let Planelico propose the circuits and the board layout.

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