RCDs, RCBOs and MCBs Explained: What's the Difference and Why It Matters
Three sets of letters that get thrown around a lot at the trade counter, and three genuinely different jobs. Here's the difference, in plain English.
MCB, Miniature Circuit Breaker
An MCB protects against overload and short circuit: too much current flowing through a cable, which would otherwise overheat it. It trips based on current (amps), rated for the circuit it protects (typically 6A for lighting, 32A for a ring final socket circuit).
RCD, Residual Current Device
An RCD protects people, not cables. It monitors for current leaking to earth, the kind of fault that happens when someone touches a live part or a cable is damaged, and cuts the supply in milliseconds. It doesn't care about overload; that's not its job.
RCBO, Residual Current Breaker with Overload protection
An RCBO is simply an MCB and an RCD combined into one device, protecting a single circuit against both faults. The main advantage over a shared RCD covering several circuits: if one circuit develops an earth fault, only that circuit trips, rather than every socket and light on that side of the consumer unit going out at once.
Which one goes where
Every final circuit in a modern domestic installation needs RCD protection of some kind, either shared or per circuit.
RCBOs are now the default recommendation for kitchens, bathrooms, outdoor sockets, and anything supplying equipment you don't want to lose power to unexpectedly (freezers, alarm systems, EV chargers).
For EV charging specifically, current guidance requires either an RCBO with Type A or Type B protection, or a charger with equivalent built-in DC fault protection. Our EV charger costs and grants guide covers what else to check before you buy.
If you're spec'ing a whole board rather than a single circuit, our consumer unit buying guide covers how many ways you'll need and what the current regulations require.
Speccing a job and want to talk it through?
Our sales team at both Stockport and Oldham deal with this daily and are happy to help you get the right combination of MCBs, RCDs and RCBOs first time, at trade prices with same-day availability on the lines we stock most. Browse our products or get in touch for a quote.
