When it comes to replacing your consumer unit (fuse box), you'll encounter various types and configurations. Understanding the differences helps you make an informed choice — and know what your electrician is recommending.
What All Modern Consumer Units Have in Common
All consumer units installed since 2016 must:
- Have a metal enclosure (to prevent fire spreading if a fault occurs inside)
- Provide RCD protection to most circuits (as required by BS 7671:2018)
- Be correctly rated for the incoming supply
Beyond these basics, the key difference is how RCD protection is provided.
The Main Types
1. Dual-RCD (Split Load) Consumer Unit
The most common type installed in UK homes over the past 15–20 years. The board has two RCDs, each covering half the circuits. This means:
- If one circuit on the left side trips its RCD, all circuits on that side lose power
- Circuits on the right side are unaffected
- Cheaper than full RCBO boards
- If one RCD trips, you lose around half your circuits
Best for: Budget-conscious installs where full RCBO protection isn't essential.
2. Full RCBO Consumer Unit
Each circuit has its own RCBO (Residual Current Breaker with Overcurrent protection) — a combined MCB and RCD in one device. This means:
- A fault on one circuit only trips that one circuit
- No nuisance tripping affecting other circuits
- Maximum protection and convenience
- Higher initial cost than dual-RCD
- Considered best practice by most qualified electricians
Best for: All new installations where budget allows — increasingly the standard choice.
3. High Integrity (Dual RCD with dedicated circuits)
A hybrid approach where most circuits are on the two RCDs, but certain critical circuits (freezer, security system, smoke alarms) are on their own RCBO. Protects critical circuits from nuisance tripping while keeping costs down.
Best for: Cost-conscious installs where a few critical circuits need dedicated protection.
The Incoming Main Switch
Above the RCDs or RCBOs sits the main switch (or main isolator) — this disconnects the entire installation from the supply. Modern boards may have a 100A main switch; if your supply is single-phase 100A, this is correct.
What About Surge Protection?
Since the 18th Edition Amendment 2 (2022), surge protection devices (SPDs) are required in most new domestic installations. An SPD protects connected equipment from voltage spikes caused by lightning or switching surges. They can be fitted to existing consumer units too.
Which Type Should You Choose?
We recommend a full RCBO board for all new consumer unit installations. The extra cost over a dual-RCD board is modest, and the benefit — never losing all your sockets and lights when a single appliance develops a fault — is significant.
Onyx Electrical Solutions installs and upgrades consumer units across Greater Manchester. Call 07000 000000 for a free quote.