Circuit Breaker vs Safety Switch: What’s the Difference?
A safety switch protects people from electric shock. A circuit breaker protects your wiring from overheating. A fuse does the same job as a circuit breaker but can only work once, then it has to be replaced. Most Australian homes need all three jobs covered, and a lot of older boards only cover one.
Key Takeaways
Safety switches protect people. Circuit breakers and fuses protect cables.
A circuit breaker will not save you from a shock. Only a safety switch will.
Safety switches should always be left in the ON position.
Ceramic and rewirable fuses are the oldest style still in service and offer no shock protection.
A safety switch that keeps tripping is usually a faulty appliance or water getting in somewhere.
The quick comparison
| Feature | Safety switch (RCD) | Circuit breaker (MCB) | Fuse |
|---|---|---|---|
| What it protects | People | Wiring and cables | Wiring and cables |
| What makes it trip | Electricity leaking to earth, such as through a person | Too much current, or a short circuit | Too much current, or a short circuit |
| How fast | Hundredths of a second | Fraction of a second | Fraction of a second |
| Reusable | Yes, flick it back on | Yes, flick it back on | No, must be replaced |
| What it looks like | Switch with a TEST button | Plain switch, no test button | Round ceramic plug or a cartridge |
| Shock protection | Yes | No | No |
If your switchboard has nothing with a TEST button on it, you have no safety switches.
What is a safety switch?
A safety switch, properly called a residual current device or RCD, constantly compares the electricity flowing out on the active wire against the electricity coming back on the neutral. In a healthy circuit those two match. If some of that current escapes somewhere else, which is exactly what happens when it travels through a person standing on the ground, the two no longer match and the RCD cuts the supply.
It does this fast enough to prevent a fatal shock. That is the whole point of the device, and it is why a safety switch is the single most important thing on a modern switchboard.
You can spot one easily. Safety switches have a small TEST button on the front. Press it and the switch should drop out straight away. If it does not, the device has failed and needs replacing. It is worth testing yours every few months.
Australian wiring rules require safety switches on new and altered circuits, which is why they get fitted as standard whenever we do a board replacement or a rewire. Older homes that have never been touched often have none at all.
You will also see a combined unit called an RCBO. That is a safety switch and a circuit breaker built into one module, so a single device covers both jobs on that circuit.
What is a circuit breaker?
A circuit breaker watches how much current is passing through a circuit. Cables are rated to carry a certain amount, and pushing more than that through them makes them heat up. Enough heat for long enough and the insulation starts to break down, which is how house fires begin behind walls.
The breaker trips before that happens. It will also trip instantly on a short circuit, where active and neutral touch directly.
What a circuit breaker will not do is notice electricity passing through a person. The amount of current it takes to kill someone is far below the amount needed to trip a breaker. That is the gap safety switches exist to fill, and it is the single most common misunderstanding we come across on the tools.
Circuit breakers are also why a full board matters. Each circuit needs its own breaker, correctly sized. When a board runs out of space, there is nowhere to add a properly protected circuit for a new oven, an air conditioner, extra powerpoints or a solar system. Doubling up or undersizing to make it fit is how dangerous boards end up that way.
What about fuses?
Fuses do the same job as a circuit breaker using a thin wire that melts. Once it melts, the fuse is finished.
The old ceramic plug style with rewirable fuse wire is the one to watch for. They are slow, they offer no shock protection, and because people sometimes replaced the wire with whatever was handy, they often no longer protect the circuit at all. If your board still has them, it is due for replacement.
Should a safety switch be on or off?
On. Always on.
A safety switch sitting in the off position is doing nothing. If one keeps dropping out and someone has left it off to stop the nuisance, that circuit is now unprotected.
Why does my safety switch keep tripping?
Usually something real, not a faulty switch. The common causes:
A failing appliance, most often a kettle, toaster, oven element or hot water unit
Water in an outdoor powerpoint or light fitting, which is why tripping often starts after rain
Several appliances on one circuit each leaking a tiny amount, adding up past the limit
Damaged cable, sometimes from a nail or a screw
A safety switch that has simply worn out
The way to find it is to unplug everything on that circuit, reset the switch, then plug items back in one at a time. If it trips with nothing plugged in, the fault is in the wiring and needs an electrician. The same applies to smoke alarms, which are hardwired and share a circuit, so a trip can leave them running on battery alone.
For businesses, repeat tripping on the same circuit is worth investigating properly rather than resetting each morning. Our commercial team can test and tag the equipment on that circuit to find the culprit.
Frequently Asked Questions
1. How often should a safety switch be tested?
Press the TEST button on each safety switch every three months. The switch should drop out immediately. If it does not, or if it will not reset afterwards, the device has failed and needs replacing. Workplaces have stricter intervals and need the test recorded.
2. Do I need both a safety switch and a circuit breaker?
Yes. They do different jobs. The circuit breaker stops your cables overheating, the safety switch stops a person being electrocuted. Neither one covers the other. Many newer boards use a combined RCBO unit so a single device handles both on that circuit.
3. How many safety switches does a house need?
There is no single number. It depends on how many circuits your home has and how they are grouped. One safety switch covering the whole house is not ideal, because a fault anywhere takes out everything. Splitting circuits across several devices keeps the lights on while you find the problem.
4. Can I install or replace a safety switch myself?
No. Any work inside a switchboard must be done by a licensed electrician, and it is illegal for a homeowner to do it in South Australia. You also get a Certificate of Compliance for Electrical Work when a licensed electrician does it, which matters for insurance.
5. Why won’t my safety switch turn back on?
The fault is still live. A safety switch will refuse to reset while current is still leaking somewhere. Unplug everything on that circuit and try again. If it still will not hold, the problem is in the wiring or in the switch itself and needs an electrician.
Not sure what is on your switchboard?
Open the cover and look for a TEST button. If there is not one, give us a call and we will tell you what you have and what it would take to make it safe.
Book a switchboard check or call 1300 640 424.