RCD vs RCBO: What's the Difference, and Does It Matter?
This is one I get asked about fairly often - usually by someone who's seen the terms on a quote, or noticed the labels inside their own consumer unit, and has no idea what either actually does. Fair enough - they sound almost identical and get used interchangeably by people who should know better.
Here's the plain version.
What an RCD does
An RCD (Residual Current Device) constantly monitors the current flowing out through a circuit and back. If it detects current escaping somewhere it shouldn't - through a person, through damp, through a fault, it cuts the power in a fraction of a second. It's primarily a life-safety device, protecting against electric shock.
What an RCBO does
An RCBO (Residual Current Breaker with Overcurrent protection) does everything an RCD does, plus what a standard circuit breaker does too — protecting against overload and short circuits - combined into a single device, dedicated to one circuit.
The practical difference that actually matters
The real-world distinction isn't really "which one is safer" - it's how many circuits share protection.
A lot of older or budget consumer units use a split-load design: one RCD covers several circuits at once. If any one of those circuits develops a fault, the RCD trips and takes out everything sharing it — so a fault in one bedroom's socket can knock out the kitchen, the hallway, and half the house with it.
An RCBO setup gives every individual circuit its own dedicated protection. A fault on one circuit trips only that circuit. Everything else stays on.
A real example of why this matters
I had a call-out in Reigate where a single faulty appliance was taking out power to the entire house every time it was used - because the property was on a split-load board, and that one circuit shared an RCD with several others. The appliance itself wasn't dangerous, just faulty, but the setup meant one fault anywhere on that shared RCD blacked out a big chunk of the home.
That's the exact situation RCBOs solve. Same fault, same faulty appliance - but on an RCBO board, only that one circuit would have gone down, and the rest of the house would never have noticed.
Is it worth upgrading to RCBOs?
Not always essential, but worth knowing about, especially if:
You've had unexplained power loss to unrelated parts of the house at the same time
You're already having consumer unit work done for another reason - it's a sensible addition to a planned upgrade rather than a separate job
You rely on certain circuits staying up independently (a home office, a fridge-freezer, anything you don't want going down because of an unrelated fault elsewhere)
Frequently Asked Questions
Is RCBO safer than RCD? Not safer in terms of shock protection - both do that job well. RCBOs are better at limiting the impact of a fault, since they isolate a single circuit instead of everything sharing an RCD.
Why did my whole house lose power from one faulty appliance? This is the classic sign of a split-load board, where one RCD covers multiple circuits. A fault anywhere on that shared RCD trips power to everything connected to it, not just the circuit with the actual problem.
Do I need RCBOs on every circuit? Not necessarily. It's most worth prioritising on circuits where you specifically don't want unrelated faults causing an outage - but a full RCBO board is the standard modern setup for new consumer units.
Can I just add one RCBO to an existing board? Sometimes, depending on the board and available space, but it's something to have assessed rather than assumed - not every existing consumer unit has room or compatibility for a partial upgrade.
