Safety switches explained: what they do, how to test them, and why one isn't enough

Most Brisbane homeowners think their switchboard has "safety switches" on it. Most Brisbane homeowners are wrong. Here's the actual rules.

What a safety switch actually does

A safety switch, properly called a Residual Current Device, or RCD, measures the current flowing out of your switchboard down the active wire, and the current coming back through the neutral. They should match. If even 30 milliamps is going somewhere it shouldn't, like through you, on its way to earth, the device snaps off in under 30 milliseconds.

That cut-off is what stops you being electrocuted by a faulty appliance.

It is not the same as a circuit breaker. A circuit breaker stops the cable from overloading and melting. An RCD stops you from being shocked. You need both. Modern RCBOs combine them in a single device per circuit.

RCD vs RCBO

• RCD, old-school. One device covering several circuits. If it trips, all those circuits go off, and you have to figure out which appliance caused it.
• RCBO, modern. One device per circuit. Combines an RCD and a circuit breaker. If your bathroom faults, your fridge stays on. This is what we install on every job.

If you open your switchboard and the test buttons are sparse, say, two test buttons covering a board with eight circuits, you have shared RCDs. That's the old way and it's due an upgrade.

How many do you need?

Under AS/NZS 3000:2018, every final sub-circuit in a domestic installation should be RCD-protected. So:

• Lighting, yes
• Power, yes
• Oven, yes
• Hot water, yes
• AC, yes
• Pool, yes
• Even the doorbell, yes

That means a typical Brisbane 3-bedroom home should have 8 to 12 RCBOs in the board, not the "one or two RCDs" that 1990s boards have.

If you don't, that's a switchboard upgrade waiting to happen.

How to test yours

Every six months:

1. Open your switchboard.
2. Find the small button labelled "T" or "Test".
3. Press it firmly.
4. The switch should snap immediately to the "off" position.
5. Reset it.

If it doesn't snap off, it's no longer protecting that circuit. Ring 0411 054 811, we'll come and replace it (usually $240 fitted).

If you have multiple safety switches, test each one separately.

Rentals: the QLD requirement

Under QLD law, every rental property must have at least one functioning RCD on power circuits and one on lighting circuits, tested at the start of every new lease. Property managers typically push the cost onto the landlord and the testing onto a sparky, that's us. We do rental safety inspections starting at $190 and email you the certificate same-day.

, John