What is the difference between a residual current device (RCD) and a residual circuit breaker with overcurrent protection (RCBO)?

These two devices keep your wiring safe. Put simply, the first has one function, and the second has two. Let’s have a look at them:

A residual current device

A residual current device monitors your wiring installation permanently to detect any leaking current. How? It continuously measures the amount of current passing through a wire in one direction, and again through a different wire in the opposite direction.

• If it detects a difference greater than 300 mA (milliamps), or less in certain cases, it breaks the circuit.
• If current is “missing”, it means there is a leak somewhere in the wiring installation. If this current leaks through a person’s body, it could lead to a potentially fatal electrocution.

Residual current devices protect people.

A residual circuit breaker with overcurrent protection

This is a protective device which combines two functions. It acts as a residual current device and a circuit breaker.

• A circuit breaker breaks the circuit if the current demand gets too high.
  How? The circuit breaker is set at the capacity of the wires in the circuit it protects. If there is an overload caused by e.g. a short circuit or excessive demand caused by plugging in too many devices on the same circuit, it reacts. Without this protection, the wires could melt and catch fire.
  Circuit breakers protect equipment and buildings.
   
• The residual current device functions in the same way as described above.
  Residual current devices protect people.

So residual circuit breakers with overcurrent protection protect people, equipment and building.

So which should I choose?

Legislation requires: 

• a 100-300 mA RCD covering the whole installation
• a second 10-30 mA RCD covering circuits in wet rooms (kitchen, bathroom, utility room, etc.)
• circuit breakers on each circuit.

However, you can meet these specifications and save space on the circuit breaker panel: on some circuits, you can replace two devices (RCD and circuit breaker) with a single device (RCBO). This will protect these circuits against current leaks and overloads at the same time.