What is an RCD, and why does it save lives?

A breaker protects the circuit; an RCD protects you. How to tell whether you have one and whether it works.

If your panel has a wider unit next to the breakers with a button marked "T" or "Test", it is very likely a residual current device (RCD).

What does it do?

If some current starts flowing to earth through the body of an appliance, or through a person, instead of its proper path, the RCD notices within a fraction of a second and cuts the power. A breaker only trips on overload and short circuits; it doesn't give the same protection against electric shock.

How to tell it works

Press the test button on the RCD. It should trip and cut the power to the circuits it protects. Then switch it back on. Doing this every few months is enough.

When to call an electrician

If it doesn't trip when you press the test button,
If your panel has no RCD at all,
If it trips often for no clear reason.

These call for a replacement or a search for leakage on the circuits. An RCD also needs sound earthing to work properly.