Electrical
MCB vs RCD vs RCBO vs MCCB: What Each Protective Device Does
Short answer
An MCB protects a circuit from overload and short circuit. An RCD detects leakage current to earth and protects people from shock. An RCBO combines both in one device for a single circuit. An MCCB is a larger moulded-case breaker for high-current circuits such as main incomers and industrial feeders.
Side by side
| Device | Protects against | Typical use |
|---|---|---|
| MCB (miniature circuit breaker) | Overload and short circuit | Individual circuits up to about 125 A |
| RCD (residual current device) | Earth leakage and shock | Groups of circuits or sockets, typically 30 mA |
| RCBO | Overload, short circuit and earth leakage | Single circuits needing both |
| MCCB (moulded-case circuit breaker) | Overload and short circuit at higher currents | Main incomers, large motors, industrial boards |
Why combine them
An RCD alone does not protect against overload or short circuit, so it is normally used together with MCBs. RCBOs protect each circuit individually, so a fault on one circuit does not switch off the others.
Choosing for your property
- Homes: an RCD or RCBOs on socket and outdoor circuits plus MCBs on others.
- Larger buildings: MCCBs on main feeders and MCBs, RCBOs on final circuits.
- Industrial: MCCBs, motor protection and discrimination between devices.
Related
See earthing and RCDs, why breakers trip and industrial electrical services.
Common questions
Do I need both an MCB and an RCD?
Yes, they protect against different things. An RCBO combines both functions.
What does 30 mA mean on an RCD?
It is the leakage current at which it trips, chosen to protect people from dangerous shock.
Can I replace an MCB with a bigger one?
No. The breaker rating must match the cable and load.