An RCBO is a protective device fitted in a consumer unit that combines the protective roles of an MCB (short circuit and overcurrent protection) with the additional electric shock protection of an RCD. This device takes up the same amount of room inside a consumer unit enclosure (one module), so it is possible to have a smaller enclosure without the need for separate RCDs.
RCBOs address the issue of nuisance tripping – the disconnection of unaffected circuits by a fault on an unrelated circuit – as each circuit is independently protected, in effect, each RCBO is ‘unaware’ of the existence of other circuits in the installation or property. This increases the compliance with the 18th edition – the current version – of BS7671.
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All of the advantages of RCDs with none of the disadvantages.
An RCBO will have a test button (as will any RCD), and this should be used every six months to ensure that the electrical supply is disconnected. Carrying out this test will confirm the correct operation of the device and will also ensure that the mechanical parts of the device are not in danger of seizing up through lack of use, as may be the case otherwise.
The ‘standard’ current configuration for a replacement consumer unit is each circuit protected by its own RCBO, with the entire property protected by a surge protection device (SPD). For those looking for the highest level of protection currently available or those in a property with a higher level of fire risk, please read about arc fault detection devices (AFDDs).
Key Differences
RCD Consumer Units
- Shared protection
- Lower cost
- Multiple circuits trip together
RCBO Consumer Units
- Individual circuit protection
- Higher cost
- Only the affected circuit trips
Which is Better?
Choose RCD if:
- You’re on a tight budget
- Simpler installation
Choose RCBO if:
- You want better reliability
- Reduced disruption during faults
- Higher safety standards
Most electricians now prefer RCBO setups.
Cost Difference
- RCD units → cheaper upfront
- RCBO units → higher cost but better long-term value
Real-World Example
With an RCD unit:
- A fault in one circuit can cut power to multiple areas
With an RCBO unit:
- Only the faulty circuit is affected
Final Verdict
While RCD units are still used, RCBO consumer units offer:
- Better fault isolation
- Improved convenience
- Higher safety standards
For most modern installations, RCBO is the preferred choice
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