RCD, RCBO or SPD: How to Choose a Consumer Unit

If you're specifying or replacing a consumer unit and want to understand the difference between RCD, RCBO and SPD boards — this is the plain-language guide. No padding, just what matters for the job.

What is a Consumer Unit?

A consumer unit (CU) — also called a fuse box or distribution board — is the main point where electricity from the supply enters a property and gets distributed to individual circuits. It contains the main switch, protective devices for each circuit, and (in modern installations) earth fault protection.

In the UK, consumer units must comply with BS 7671 (the IET Wiring Regulations). Since the 18th Edition came into force in January 2019, there are specific requirements around surge protection and the type of protective devices used.

Types of Consumer Unit: What's the Difference?

RCD Consumer Units

An RCD (Residual Current Device) monitors the difference in current flowing in and out of a circuit. If it detects a fault — even a small one — it trips in milliseconds, protecting against electric shock and reducing fire risk.

Split load boards are the most common RCD configuration: the board is divided into two halves, each protected by an RCD. This means a fault on one circuit only trips half the board, not the entire property. Standard for most domestic and light commercial installs.

High integrity boards take this further — they have three RCDs (or more), so a fault on a single circuit affects fewer other circuits. Good for critical installations where losing lighting on a trip is unacceptable.

RCBO Consumer Units

An RCBO (Residual Current Breaker with Overcurrent) combines an MCB and RCD in a single device per circuit. Every circuit has its own independent fault protection.

This is the premium option: a fault on any circuit trips only that circuit. No nuisance tripping of other circuits. More expensive per board, but increasingly specified — particularly for larger domestic installs, HMOs, and any job where the client can't afford to lose lighting when the washing machine trips.

All RCBO boards comply with 18th Edition requirements for individual circuit protection.

SPD Consumer Units (18th Edition)

An SPD (Surge Protection Device) is designed to protect against transient voltage spikes — typically caused by lightning strikes or switching surges in the supply network. These spikes can destroy sensitive electronics (smart home systems, LED drivers, appliances) in seconds.

The 18th Edition Amendment 2 (effective January 2022) strengthened the requirements: SPDs are now required in most new and rewired domestic and commercial installations, unless a risk assessment demonstrates they're not needed.

In practice: if you're rewiring a house or replacing a board, you should be fitting an SPD. Some boards come with SPD built in (Type 1+2 combined). Others require a separate Type 2 SPD device to be fitted.

Hager Consumer Units: In Stock at APM

Hager is a premium board brand that Screwfix doesn't stock. We do — and for collection from our Acton trade counter same day.

Hager boards are well-regarded by electricians for build quality, busbar design, and clear labelling. The FuseBox range (which we also stock) offers strong value — the FuseBox 10-way SPD board at £75.80 is a consistent seller, and undercuts Toolstation's equivalent by £37.

If you're quoting a consumer unit job and want to check what we have on the shelf before committing, call us on 020 8702 8080.

When Do You Need to Replace a Consumer Unit?

Common triggers for a CU replacement:

• Old rewireable fuse board (ceramic fuse carriers) — no longer adequate for modern protection requirements
• Adding circuits that exceed the current board's capacity
• EV charger installation — most require a dedicated circuit from a modern board
• Solar PV or battery storage install
• Full or partial rewire
• EICR (Electrical Installation Condition Report) identifying C1 or C2 defects at the board
• Upgrading to RCBO protection to reduce nuisance tripping

Any consumer unit replacement is notifiable work under Part P of the Building Regulations. It must be carried out by a competent person registered with a Part P scheme (NICEIC, NAPIT, ELECSA, etc.) or notified to the local authority.

Quick Spec Reference

In Stock at APM — Acton Trade Counter

We stock Hager and FuseBox consumer units for same-day collection. No ordering ahead required — walk in, check what we have, take it today.

APM Plumbing & Electrical Supplies
24 Western Avenue, Acton, London W3 7TZ
📞 020 8702 8080 | 🌐 apmi.uk
Mon–Sat, trade counter open