Ever wondered how a circuit breaker actually works? We are here to tell you all about this devices and how they safeguard your property. We explore the inner workings of circuit breakers, shed light on their importance in electrical systems, and highlight their role in ensuring safety.
Switchboards in Sydney may come in different brands, sizes, and materials, but they are mostly seen as a row of many small switches that control specific areas of the house.
But as the main component that houses circuit breakers for each power point, they do more than distribute power. They also play a very crucial role in electrical safety and protecting your household from electrical faults.
A circuit breaker automatically cuts the power and trips off the downstream power points in the event of an electrical fault or overloading.
What makes circuit breakers important is that without them, constantly using high-draw appliances like ovens, dryers, and heaters may overload your wiring and melt the electrical insulation off your wires, causing heat or an electrical fire behind the walls.
In this blog post, we break down what happens inside a circuit breaker, why the mechanism matters, and how a breaker differs from the safety switch next to it on the board.
Circuit breakers protect your power system from two types of electrical faults. To do so, they have two separate mechanisms working to disconnect the circuit, as these two faults happen on different occasions.
A circuit breaker has a bimetallic strip, which is two different metals bonded together in a single strip.
If you’re running too much current on this circuit for a long time, the bimetallic strip heats up to a certain threshold where the strip bends too far out, pushing the trip lever and opening the circuit.
It’s a slow, thermal response to a slow, thermal problem, and that’s deliberate. You don’t want the breaker dropping out every time the fridge compressor kicks in.
A long-term high-current draw overheat is different from a short circuit incident. When a short circuit occurs, you only have a few milliseconds from the actual event to a spreading electrical fire.
A circuit breaker prevents this from happening through an electromagnetic coil wrapped around an iron core. When a short circuit occurs, this coil gets energised instantly, causing it to yank the trip bar open in as fast as thousandths of a second.
When electrical contacts carrying the full electrical current are suddenly pulled apart, the electricity bridges the two terminals as an electrical arc that’s hot enough to melt metal.
To avoid this electrical arc damaging the other components inside your circuit breaker, an arc chute, which is a stack of thin metal plates, is installed just above or behind both electrical contacts.
Its job is to absorb that arc and split it into several smaller ones, stretching them and quickly cooling them to avoid the arc causing a fire inside your switchboard.
As circuit breakers are designed to protect against two severe electrical faults, it’s safe to say they are necessary for all households. To dig deeper into that, here’s why a circuit breaker earns its place.
The thermoplastic insulation on standard household cable is rated to operate at around 75°C. If you push current above what the circuit was designed to carry, the copper conductors will run hot, and the insulation starts to soften, causing them to degrade, melt, then fail.
Unlike short circuits and electrical arcs, electrical fire caused by overloading and overheating is dangerous and expensive, as it happens out of sight. You also won’t notice any symptoms until the damage is severe.
By the time you smell burnt plastic or rubber, the damage is done. A breaker interrupting that overload before the cable reaches its limit is therefore vital in ensuring your property is protected against electrical overheating.
A short circuit occurring inside an air conditioner, an electric oven, or a computer power supply dumps a significant amount of energy into a very small space very quickly.
To avoid causing severe and irreparable damage to electrical devices and components, a circuit breaker acts by cutting the supply in milliseconds. This helps contain the transient currents immediately and keep your electrical appliances and electronics safe from expensive repairs or replacement.
Plenty of older Sydney homes still run rewireable ceramic fuses, and it’s worth understanding what was wrong with them.
A fuse does the same basic job by melting a thin wire, which works. The problems are that it isn’t resettable, it isn’t especially precise, and critically, the fuse wire is user-replaceable.
Anyone who has ever “fixed” a nuisance-blowing fuse by fitting a heavier gauge of wire has silently removed the protection from that circuit while leaving something that still looks like a working fuse.
A modern breaker can’t be defeated that way. It trips at its rating, it resets with a flick, and you can see at a glance which circuit dropped out.
A circuit breaker and a safety switch may be mounted inside a modern switchboard all together without you being able to notice the difference. But while some of them look very similar to each other, they do entirely different jobs and respond differently to different types of electrical faults.
Circuit Breakers protect your wiring and appliances by detecting events such as electrical overload and short circuits. That means they mainly protect your wiring and electrical appliances from irreparable damage.
A safety switch or RCD, on the other hand, protects people from electrical shock by tripping off in the event of an earth fault.
When they don’t, current is leaving the circuit somewhere it shouldn’t, and the most common reason for that is a human being providing a path to earth. The RCD cuts power within milliseconds of detecting as little as 30mA of leakage [1].
|
Circuit breaker |
Safety switch (RCD) |
RCBO |
|
|
Protects wiring from overload |
Yes |
No |
Yes |
|
Protects wiring from short circuit |
Yes |
No |
Yes |
|
Protects people from shock |
No |
Yes |
Yes |
|
Has a test button |
No |
Yes |
Yes |
A residual current circuit breaker with overload protection, or RCBO, is a combination device that does both the tasks of circuit breakers and safety switches in one module.
It’s why modern switchboard installations also include RCBOs by default rather than a standalone breaker, and why a like-for-like breaker replacement on an old board is usually a missed opportunity.
One way of knowing whether you have a circuit breaker, a safety switch or an RCBO is by looking for a test button in your switchboard. All RCDs and RCBOs have one in front, usually marked T for test.
Circuit Breakers don’t have a test button. So if you’re looking at your board and you don’t see any test button anywhere, that means you only have a circuit breaker installed without any safety switch or RCBO.
By knowing what type of protective system you have in your switchboard, you now have an informed decision on whether to call a licensed electrician to upgrade your switchboard and install the appropriate protective equipment [2].
Three things cut the power, and being able to tell them apart saves a lot of unnecessary worry.
|
What happened |
Most likely cause |
What to do |
|
Tripped once when you plugged something in |
Overload on that circuit |
Reset it, spread the load |
|
Trips instantly every time you reset |
Short circuit or faulty breaker |
Unplug everything, then call someone |
|
Trips only when one appliance runs |
Fault in that appliance |
Stop using it, get it checked |
|
Trips with nothing plugged in |
Fixed wiring or the breaker itself |
Leave it off, book fault finding |
Here’s the reassuring part: a single trip, once, after a storm or when you plugged in something new, is usually nothing at all.
Reset it and carry on. What’s worth acting on is a pattern. A breaker that trips repeatedly, trips with nothing plugged in, or won’t reset at all is telling you about a real fault, and that’s a job for electrical fault finding rather than repeated resetting.
Yes, circuit breakers are made with mechanical springs, latches and bimetallic strips that all work mechanically to physically disconnect the circuit in the event of an overload or a short circuit.
That means all of its internal components may wear out over decades of resets and trips. A worn breaker can start acting or responding below its rated load and, worse, fail to trip in a real electrical emergency.
A breaker carrying a heavy load is expected to run slightly warm, and that is normal. However, if it’s hot to the touch and you hear a buzzing sound or smell a very faint odour of molten plastic, then those are signs of an emergency.
Those symptoms may point to a loose connection or damaged internal contacts that create resistance. You need to have your circuit breaker looked at as soon as possible instead of monitoring the issue.
Unplug everything that’s connected to that circuit breaker and reset it. If it stays on, start plugging appliances in one at a time and identify which device causes it to trip off.
If nothing causes it to trip, then the fault may be inside the breaker itself or the wiring behind the walls. In that case, you need an electrician to inspect the wiring rather than do another annoying reset.
No, ceramic fuses that already exist in your wiring are not illegal to keep in place. However, should you decide to upgrade or modify your circuit, you must comply with the modern wiring rules [3].
That said, any new circuit board upgrade or power point relocation and installation should have dedicated RCD protection in place rather than installing ceramic fuses on new connections.
Once in a while, yes. A breaker that drops out during a storm or when you plug in a new heater has done its job and resetting it is fine. Repeatedly resetting one that keeps tripping is different, because you’re overriding a warning rather than clearing one, and each heavy trip wears the mechanism a little further. Two or three resets is your limit before it’s worth a look.
Circuit breakers are one of the best pieces of safety engineering in an ordinary house, right up until age, wear, or a board that predates the current standard stops them doing the job properly. Most of the time they’re fine and a single trip means nothing.
If yours are decades old, tripping for no reason you can find, or you simply don’t know what’s protecting your circuits, book a switchboard upgrade or a home electrical inspection with Bright Force Electrical, or call us on 1300 724 942.
Our technicians are in-house and licensed; there’s no call-out fee during business hours, and you get a fixed price after we’ve seen the board.
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