Safety Switch vs Circuit Breaker: What's the Difference?

A circuit breaker protects your wiring; a safety switch protects people. A circuit breaker switches off when too much current flows through a circuit, preventing cables from overheating. A safety switch (also called an RCD, or residual current device) switches off almost instantly when it detects electricity leaking to earth, such as through a person touching a live part. Most modern homes need both.

How a circuit breaker works

Each circuit in your switchboard has a circuit breaker rated to suit the size of its cable. If you overload the circuit or there's a short circuit, the current rises above that rating and the breaker trips. This stops the wiring overheating and potentially starting a fire inside a wall or ceiling.

What a circuit breaker can't do is detect the small amount of current that flows through a human body during an electric shock. That current can be fatal yet far below the level that would trip a breaker.

How a safety switch works

A safety switch constantly compares the current going out on the active conductor with the current returning on the neutral. In a healthy circuit they're equal. If some current is leaking away to earth, through faulty insulation, a damaged appliance, water or a person, the RCD detects the imbalance and cuts power, typically within a fraction of a second. Household RCDs are generally set to trip at 30 milliamps, low enough to greatly reduce the risk of a fatal shock.

How to tell them apart in your switchboard

• Safety switches have a "Test" or "T" button and are often labelled "RCD", "RCBO" or "Safety Switch".
• Circuit breakers have just a switch, and are usually labelled with a current rating such as 16A or 20A.
• Combination devices (RCBOs) do both jobs for a single circuit, and also have a test button.
• Ceramic fuses are an older form of circuit protection with no shock protection at all.

Why you need both

They protect against different dangers. A circuit can be perfectly within its current rating while still delivering a fatal shock through a person, which only an RCD will catch. And a circuit can be dangerously overloaded without any earth leakage, which only a breaker will catch. That's why current Australian wiring rules require RCD protection on final subcircuits in new and altered installations, alongside circuit breakers.

Which one has tripped?

If a safety switch trips: it's usually caused by a faulty appliance, moisture (for example in an outdoor power point after rain) or damaged wiring. Unplug everything on the affected circuits, reset the switch, then plug items back in one at a time to find the culprit.

If a circuit breaker trips: it's usually overload or a short circuit. Reduce the load on that circuit and reset. See why circuit breakers keep tripping for more detail.

If either won't reset, trips again immediately, or trips without an obvious cause, call a licensed electrician rather than repeatedly resetting it.

Test your safety switches regularly

Press the "Test" button on each safety switch every three months or so, or as the manufacturer recommends. It should trip immediately. Switch it back on afterwards. If it doesn't trip, it isn't protecting you and should be checked by an electrician. Expect to reset clocks on appliances afterwards.

Does your home have enough protection?

Many older Melbourne homes have one safety switch covering only the power points, or none at all. Lighting circuits, hot water, cooking and air conditioning circuits may be unprotected. Our guide on whether your home has enough safety switches explains what to look for, and in rental properties, RCDs are part of the Victorian minimum standards (see landlord electrical obligations).

Adding safety switches is often done as part of a switchboard upgrade. VU Electrical can check your current protection and recommend what's needed.