MCB: the overload guard
A miniature circuit breaker (MCB) protects a circuit's wiring from too much current – an overload or a short circuit. Plug in too many high-power things on one circuit and the MCB switches off before the cable gets dangerously hot.
What it doesn't do is protect people from electric shock caused by current leaking to earth. That's a different job.
RCD: the people protector
A residual current device (RCD) watches for electricity leaking out of a circuit – through damaged insulation, water or a person – and cuts the power almost instantly. In many homes, one RCD protects a group of circuits, which is why a single faulty appliance can sometimes knock out several rooms at once.
Need an electrician?
Describe the job and compare free quotes from local electricians near you.
- Free to use
- No obligation
- Compare local electricians
- Quick online form
You'll continue to our quotes partner, MyJobQuote, to describe your electrical job.
RCBO: both in one
An RCBO combines an MCB and an RCD for a single circuit. If something goes wrong, only that circuit goes off. A fault in the garden lights won't plunge the kitchen into darkness, and finding the problem is quicker.
Boards with an RCBO on every circuit cost more than boards with shared RCDs, but many people think the convenience is worth it, especially in homes where nuisance trips have been a headache.
| Device | Overload and short circuit | Earth leakage (shock) | If it trips |
|---|---|---|---|
| MCB | Yes | No | One circuit goes off |
| RCD | No | Yes | Every circuit it covers goes off |
| RCBO | Yes | Yes | Only its own circuit goes off |
What each device protects against
Which is right for you?
If you're replacing a consumer unit, ask electricians to quote for both a split-load board with shared RCDs and an RCBO board. Then you can weigh up cost against convenience. Either way, the work should be tested and certified.
