What Is an RCBO, and How Is It Different From an RCD?
Opened the fuse box and seen switches marked RCBO? Or been told a new board would have RCBOs, and not sure what that changes? This guide explains what an RCBO does, how it differs from an RCD, and what it means when one trips.
Send a photo of your fuse box if you want to know what is in yours.
Two jobs inside your fuse box
A fuse box, or consumer unit, protects each circuit in your home in two different ways. The IET explains that circuit breakers, the modern equivalent of fuses, protect against overcurrent and short-circuit faults, and that there is one for each circuit. RCDs are there to protect people from electric shock.
Electrical Safety First says an RCD watches for current leaking where it should not and can cut the power in as little as 40 milliseconds.
An RCBO does both jobs in one device, for one circuit. Manufacturer documentation describes it as a circuit breaker and an RCD combined, giving overcurrent protection and leakage (earth fault) protection in a single unit.
RCBO vs RCD: what changes when something trips
Many fuse boxes have one or two RCDs, each protecting a group of circuits. The IET explains that if one RCD operates, the circuits on the other keep working. Everything on the RCD that tripped goes off together.
Shared RCD. A fault on one circuit can switch off every circuit on that RCD, for example the lights and sockets in half the house.
RCBO. A fault switches off its own circuit only. The rest of the house stays on.
The manufacturer documentation puts it the same way: an RCBO limits leakage protection to a single circuit, so only the circuit with the fault is interrupted. If a shared RCD keeps going off, the RCD keeps tripping guide explains what usually causes it and what is safe to check.
How to tell what is in your fuse box
Each switch is usually labelled on its front. If the labels are missing or hard to read, a photo of the fuse box with the switches showing is usually enough for an electrician to tell you whether you have RCDs, RCBOs or older fuses.
Do not take the cover off the fuse box. Opening the front flap to look at the switches is fine. Anything behind the cover is a job for a registered electrician.
Breaker and fuse board jobs AJS has done
Checkatrade reviews for AJS include an RCBO replacement, a car charger circuit breaker that needed a new part, and fuse board replacements. When the whole board needs changing, consumer unit upgrades explains how that is decided.
Every review here is copied word for word from Checkatrade. You can read the full list on Checkatrade and Google.
An RCBO that needed replacing
“I had a RCBO that needed replacing, a little but important job, and Alex fitted it in within a few hours of me agreeing the quote. The work was done very competently and efficiently and at a reasonable price.”
Checkatrade review, RCBO replacement, CR5
A breaker on a car charger circuit
“Tesla charger circuit breaker was not working correctly meaning we couldn’t charge our car. Alex responded on the same day immediately despite it being the weekend, and could come out within 48 hours to come and look at it. He identified the problem and ordered a new part, and as soon as it arrived arranged to come and fit it straight away. Thanks for your help.”
Checkatrade review, Tesla charger circuit breaker needed repair, RH2
A fuse board upgrade
“Really pleased with work done by AJS. Very professional, punctual and communicative.”
Checkatrade review, fuseboard upgrade, RH2
A consumer unit replacement
“Very quick to reply, quote and fit us in. Alex was friendly and very tidy worker. Would use again.”
Checkatrade review, replacement of consumer unit, RH6
Common questions
Is an RCBO better than an RCD?
Both give leakage protection. The difference is how much switches off when there is a fault: an RCBO switches off one circuit, a shared RCD switches off its whole group. Which suits a home depends on the board and the circuits, and an electrician can tell you what yours has.
Do i need RCBOs?
Not necessarily. A board with RCDs also gives leakage protection. Whether RCBOs make sense depends on the board and the circuits, and is part of what an electrician looks at when a board is replaced. The consumer unit upgrades page explains how that works.
One RCBO keeps tripping. What does it mean?
It has switched off its own circuit because it has seen too much current or current leaking on that circuit. Unplug anything on that circuit and reset it once. If it trips again, leave it off and have the circuit checked. Fault finding and repairs explains how the cause is traced.
Can i replace an RCBO myself?
No. Work inside the fuse box is for a registered electrician. The IET advises using a registered electrical contractor for problems such as a device that trips and will not reset.
What should i send?
A photo of the fuse box with the switches and any labels showing, and a note of what tripped and when.
Not sure what is in your fuse box?
Send a photo of it on WhatsApp with a note of what you want to know, or call. It is the same process whichever of the electrical services available you need.