Safety Switches
vs Circuit Breakers

This is the question we answer most often standing in front of an open switchboard. People assume that because the board has rows of switches, the house is protected. Sometimes it is. Often it is only the wiring that is protected.

Circuit breakers protect the wiring

A circuit breaker watches how much current is flowing through a circuit. If the load exceeds the rating of the cable, or there is a short circuit, it trips and stops the cable overheating. That prevents fires. It does an important job and it does it well.

What it does not do is notice you. The current that will kill a person is a tiny fraction of what it takes to trip a breaker. You can be electrocuted on a circuit whose breaker never moves.

Safety switches protect people

A safety switch, properly called a residual current device or RCD, compares the current flowing out to the current returning. In a healthy circuit they match. If some current is leaking to earth, through a damaged cable, a wet appliance, or a person, the two no longer match and the RCD cuts power in around 30 milliseconds.

A circuit breaker asks how much current is flowing. A safety switch asks where it is going. That difference is the whole point.

How to tell what you have

Open your switchboard cover and look at the devices. Breakers are plain switches. RCDs have a test button, usually marked T or TEST, and often a slightly wider body. Combination devices called RCBOs do both jobs in one unit and are what we fit on modern boards, one per circuit.

• Test button present: you have RCD protection on that circuit
• Plain switch, no test button: circuit breaker only
• Ceramic fuses: neither, and the board is well overdue
• One RCD covering the whole board: better than nothing, but a single fault takes out the entire house

How to test yours

Press the test button on each RCD. It should trip immediately and cut power to its circuits. Reset it and check that power returns. Doing this every three months is worth the two minutes, because an RCD that has sat untested for fifteen years may have seized.

If pressing test does nothing, the device has failed and the circuit is effectively unprotected. That is a call to make today, not at your convenience.

Why one RCD is not enough

Older boards often have a single RCD protecting everything. It meets a minimum, but when one faulty appliance trips it, the whole house goes dark, including the fridge and the freezer, and finding the fault means turning circuits off one at a time. Individual RCBOs isolate only the affected circuit, which is both safer and far more practical.

What the rules require

Current wiring rules require RCD protection on new and altered circuits, and there are specific requirements when properties are sold or leased. Most homes built before the mid nineties will not comply without an upgrade. We assess this as part of any switchboard upgrade and will tell you exactly what your board has and what it is missing.

If you are also checking your smoke alarms, read our summary of Queensland smoke alarm laws — the two items are usually addressed in the same visit.