Residual Current Devices   

A residual current device, or RCD, combines a protective circuit with a simple electrical tester. Built very similarly to a power transformer, the RCD sits in your fuse box and constantly monitors the incoming current in the mains. The moment the current drops it shuts everything on that circuit off.   

What's the Difference Between an RCD and a Circuit Breaker?   

While RCDs and circuit breakers can both shut off the power from the mains to your appliance when necessary, they do so for different reasons:   

Residual Current Devices: The purpose of an RCD is to protect you from problems in the mains. They trip when your electricity supply has a problem.   

Circuit Breakers: Circuit breakers kick in when you draw too much power from a circuit, either by plugging in too many devices or when one fails and draws too much.   

Installing an RCD 

Some homes already have them built into the wiring, but you can also add your own. Many manufacturers offer circuit breakers with RCDs built in, to provide dual protection for your home and equipment.