In short
A fuse and a circuit breaker protect the wiring: each cuts the power when too much current flows, from an overload or a short circuit. A safety switch (RCD) protects people: it turns the power off in a fraction of a second when electricity leaks to earth at a harmful level, typically 30 milliamps or less. The NSW Government recommends safety switches on all circuits.
If you would rather have it checked, Ambient Electrical offers safety switch installation in Sydney's Eastern Suburbs.
What is a switchboard?
The switchboard, often still called the fuse box, is where the power coming into your home is split into circuits, each with its own protection: rewireable fuses on an old board, circuit breakers and safety switches on a newer one.
What is a fuse box?
A fuse box is an older switchboard that protects each circuit with a rewireable fuse: a ceramic carrier holding a length of fuse wire that melts when too much current flows. It protects the wiring, not people, and blown fuses are often rewired with the wrong gauge of wire. Replacing an old switchboard swaps the fuses for circuit breakers and safety switches.
How a safety switch (RCD) works
A safety switch, or residual current device (RCD), turns the power off in a fraction of a second when it detects electricity leaking to earth at a harmful level, typically 30 milliamps or less. It monitors the flow of electricity through a circuit, comparing the current going out with the current coming back, and a difference means some is leaking away, which is what happens when current flows through a person.
| Device | What it protects | How it works |
|---|---|---|
| Rewireable (ceramic) fuse | The wiring, against overload and short circuits | A fuse wire melts when too much current flows. It does nothing to protect a person from an electric shock, and blown fuses are often rewired with the wrong gauge of wire. |
| Circuit breaker | The wiring, against overload and short circuits | Switches the circuit off when too much current flows, and is switched back on rather than rewired. On its own it does not protect a person from an electric shock. |
| Safety switch (RCD) | People, against electric shock | Compares the current going out with the current coming back, and turns the power off in a fraction of a second when electricity leaks to earth at a harmful level, typically 30 milliamps or less. |
Source: NSW Government: Electrical safety in the home; SafeWork NSW: Managing electrical risks in the workplace, code of practice (PDF). Fuse and circuit breaker rows: Peter Stafford's switchboard page.
Which do I need?
Both. Circuit breakers stop the wiring overheating; safety switches protect the people using it. For full protection, the NSW Government says to have safety switches installed on all your circuits by a licensed electrician. Older homes often have one safety switch covering everything, or none: safety switch installation closes the gap.
A surge protector is a different device again: it deals with brief voltage spikes and is covered on the surge protection page.
Testing your safety switches
The NSW Government recommends testing safety switches twice a year: press the TEST button on each one and it should switch off straight away. Tell the household first, check the lights and appliances on that circuit have gone off, then push the switch back to on. If one keeps tripping on its own, see the guide to a safety switch that keeps tripping.
