If you are looking at upgrading your consumer unit, you will probably hear your electrician talk about RCDs, RCBOs and surge protection. Understanding the difference helps you choose a setup that is safe, reliable and ready for future additions like EV chargers or solar.
RCDs and RCBOs explained in plain English
RCD stands for Residual Current Device. Its main job is to protect people from electric shock and reduce the risk of fire by detecting earth leakage, such as when current starts flowing somewhere it should not, like through a damaged cable or a person.
RCBO stands for Residual Current Circuit Breaker with Overcurrent protection. It does the same shock and earth leakage protection as an RCD, but it also includes overcurrent protection like a standard MCB. That means it trips for overloads and short circuits on that circuit as well.
RCD: Protects against electric shock and earth leakage, usually covering several circuits together.
MCB: Protects a single circuit against overload and short circuit only.
RCBO: Combines RCD and MCB functions for one individual circuit.
Both RCDs and RCBOs are designed to cut the power quickly in dangerous situations. The difference is how many circuits they cover and what type of faults they monitor.
How RCD consumer units are typically arranged
Many homes have what is often called a split-load or dual RCD consumer unit. In this layout, the circuits are divided into two groups, each protected by its own main RCD and individual MCBs.
In normal use, this setup is safe and compliant when correctly designed and tested. However, it can lead to what people often refer to as “nuisance tripping”, especially if several circuits share one RCD and a minor fault occurs.
What Happens When One Fault Trips Half the House?
Imagine a single socket in the kitchen develops an earth leakage fault. On a split-load RCD board, that one fault can cause the RCD to trip and turn off all the circuits on that side of the board in one go.
You might suddenly lose power to half the lighting, some sockets, the boiler controls and possibly your fridge, even though only one socket is actually faulty. Finding which circuit is to blame can take time and may need test equipment.
How an all-RCBO consumer unit works
In an all-RCBO consumer unit, each circuit has its own RCBO. There is still a main switch, and often a surge protection device, but there are no large shared RCDs that cover multiple circuits together.
Because every circuit has its own combined shock and overcurrent protection, a fault only affects the circuit where it occurs. This changes the way the board behaves when there is a problem.
When a Single Circuit Trips Alone
Using the same faulty kitchen socket example, with an all-RCBO setup only the RCBO for the kitchen socket circuit will trip. Your lights, boiler and other sockets stay on.
This usually makes fault finding more straightforward, because the tripped device is clearly labelled for that circuit. It also reduces the inconvenience of losing power to unrelated parts of the house.
Key benefits and trade-offs of RCBOs vs RCDs
From a safety perspective, both correctly installed RCD-based and RCBO-based boards offer life-saving protection against electric shock and earth leakage. RCBO boards provide a more targeted approach, which brings some practical advantages.
Reduced nuisance tripping: With each circuit on its own RCBO, a minor fault on one circuit is less likely to take out lighting and essential appliances at the same time, which can be especially helpful at night or for vulnerable occupants.
Easier fault diagnosis: When only one RCBO trips, your electrician can immediately focus on that circuit. This can speed up testing, reduce disruption and make it clearer for you which areas of the house are affected.
Future-proofing your home: Modern homes increasingly add EV chargers, solar PV systems, battery storage, hot tubs and garden offices. Having individual RCBOs makes it simpler to add dedicated, well-labelled circuits with appropriate protection for each new load.
Board capacity and layout: RCBOs can make better use of space in some consumer units, and the way they segregate circuits can be useful for meeting current wiring regulations and manufacturers’ recommendations.
Related protection: surge protection devices (SPDs)
Surge protection devices sit in or next to the consumer unit and protect against transient overvoltages. These can be caused by nearby lightning strikes or switching events on the supply network.
An SPD helps to limit voltage spikes that could damage sensitive electronics like computers, TVs, internet equipment, heat pumps, EV chargers and smart home devices. It will not stop tripping from earth faults or overloads, but it adds another layer of protection for your equipment.
SPDs are often recommended in homes with lots of electronic devices, in rural or lightning-prone areas, and where you have valuable or critical equipment that would be costly or disruptive to replace.
Condition of your existing installation matters
Upgrading to RCBOs or adding SPDs is only part of the picture. Your existing wiring, earthing and bonding must be suitable for modern protective devices to work properly.
A professional electrician should test the installation, check that the earthing and bonding are up to standard, and confirm that existing cables and accessories are sound. If there are underlying faults, simply fitting new devices will not resolve them.
Questions to ask your electrician and paperwork to expect
Before committing to a consumer unit upgrade, it helps to have a clear conversation with your electrician. A few good questions include:
Will my circuits be on shared RCDs or individual RCBOs, and what are the pros and cons for my home?
Are you recommending a surge protection device, and if so, what will it protect?
Have you tested the existing wiring and earthing, and are any remedial works needed first?
How will the new board be labelled, and how should I reset devices safely if they trip?
After the work, you should receive an Electrical Installation Certificate (EIC) for the consumer unit change. In a domestic property in England and Wales, notifiable work should also be registered under Part P of the Building Regulations, and you should receive confirmation of this from the relevant scheme or local authority.
Get tailored advice for your home
Every property is different, and the best choice between RCD-based or all-RCBO protection depends on your wiring layout, how you use your home and any planned upgrades such as EV charging or solar panels. The most reliable answer comes from a proper on-site assessment and testing.
To talk through your options, arrange a consumer unit assessment, or ask about fault finding contact J. Durka Electrical Services on 07977479071. You can also explore our Electrical Services & Fault Finding pages for more details on how we can help keep your home safe, reliable and ready for the future.
