What is a Circuit Breaker?

Ever come across the term and asked yourself, “What is a circuit breaker?” The short answer is that it is an essential electrical safety device that protects your home. The long answer is exactly what we’re here to look at today.

A circuit breaker is a safety device designed to protect wiring and appliances from excessive current overloads and short circuits. It sits in your switchboard and guards individual circuits such as lighting, power points and major electrical appliances. When a circuit exceeds safe limits, the breaker shuts off the electrical flow to that circuit, effectively stopping damage and reducing fire risk.

Each breaker covers one circuit, so a fault does not take down the whole home. Let’s take a look at circuit breakers in closer detail.

How a Circuit Breaker Works

Knowing how a circuit breaker works is important to answering the question “What is a circuit breaker?”, so let’s take a closer look.

A basic circuit breaker consists of the following components:

• Electrical contacts
• An operating mechanism
• Tripping mechanisms and
• An arc extinguisher

During normal current flow, the moving contact touches the stationary contact, and the circuit runs. If the current exceeds the rating, the bimetallic strip bends for overloads. In a short circuit event, the magnetic trip reacts instantly.

The trip unit releases the mechanism, the contacts open, and an arc forms. The arc is pushed into the arc chute, where it cools and goes out. The circuit breaker interrupts or cuts power to that circuit, isolates the fault, and protects the wiring.

After a licensed electrician checks the cause, you can reset the breaker and restore the power supply.

Types of Circuit Breakers

You’ll see several types of circuit breakers in Australian homes, with each tailored to a specific job.

• Miniature low-voltage circuit breakers for power and lighting.
• Residual Current Device (RCD, also known as a safety switch) or Residual Current Circuit Breaker with Overcurrent Protection (RCBO)
• AFDD, arc fault circuit interrupter technology, is used to reduce fire risk. This is not mandatory in Australia, but it can be a useful and valuable addition to your electrical circuit protection arsenal.
• Digital and solid-state circuit breakers for monitoring and remote control. These are not as prominent in Australia, but can be considered as an option.

You’ll typically find other circuit breakers, like medium voltage circuit breakers and oil circuit breakers, in substations that feed neighbourhoods and networks, respectively.

Choose the right circuit breaker for your electrical system and the connected appliances.

Circuit Breaker Standards and Compliance in Australia

When it comes to installing or replacing circuit breakers in Australia, they must follow AS/NZS 3000 Wiring Rules, which set requirements for selection, installation, testing and labelling. To maintain compliance, you must always use a licensed electrician.

Standard circuit breakers for low-voltage circuits are miniature circuit breakers (MCBs) to AS/NZS 60898.1:2024. For non-domestic, higher capacity moulded case circuit breakers, they follow AS/NZS 60947.2.

RCBOs and RCDs must meet AS/NZS 61009.1 or AS/NZS 61008.1. New residential final subcircuits require 30 mA RCD protection, delivering overcurrent and short circuit protection when combined with MCBs.

Electricians verify fault loop impedance, prospective short circuit current, and device rating to ensure compliance and electrical safety.

How Electricians Size and Select Electric Circuit Breakers

Choosing the right circuit breaker starts with delegating the task to an experienced and licensed electrician who does the sizing and selection.

Your electrician begins by assessing the circuit load and cable size. That step sets the rating to protect the cable, not the appliance. Measurements at the switchboard determine the worst short-circuit current. Selection sets breaking capacity above that value.

For homes, B or C curves suit most lighting and power needs. D curve suits motors with high start-up current. When shock protection is needed, a 30 mA RCBO goes on the circuit.

Checks cover voltage rating, heat and grouping, with derating applied where required. Coordination ensures that only the faulty circuit trips. The final review confirms enclosure space, IP rating and clear labels. Commissioning verifies RCD trip times and fault-loop impedance for fast disconnection. Documentation records results and compliance with AS/NZS 3000 and the relevant device standards.

What To Do If a Circuit Breaker Trips

As we know, circuit breakers play a vital role in maintaining electrical safety throughout your home. When a circuit breaker trips, treat it as a valuable red flag that prevents electrical hazards, not as an inconvenient nuisance. As much as circuit breakers protect us and our homes, safely restoring power is also important. So here’s what to do.

• Switch off and unplug appliances on that electrical circuit to reduce current flow.
• At the circuit breaker panel, find the tripped breaker on the switchboard.
• Reset once only after, push fully to OFF, then back to the ON position.
• If it trips again, stop; the circuit exceeds its rating, or there has been an electrical fault of some kind.
• Turn loads back on one by one to find overloading or short circuits.
• Test the RCBO or RCD with the test and reset buttons.
• Look for heat or scorch marks, and do not touch damaged equipment.

If problems persist, call a licensed electrician to restore overcurrent protection and electrical safety.

Stay Safe with the Right Circuit Breaker Technology

Choosing and installing the right circuit breaker keeps your home safe and your electrical system compliant. You’ll find this electrical safety device situated in the switchboard, watching current flow and acting when an electrical fault occurs.

If an electric circuit exceeds its rating, the breaker trips and interrupts current flow, stopping overheating and reducing the risk of electrical fires.

When in doubt about types of circuit breakers or coordination, ask a licensed electrician to verify.

Please note: Thanks for reading our blog “What is a Circuit Breaker?”. This information is provided for advice purposes only. Regulations differ from state to state, so please consult your local authorities or an industry professional before proceeding with any work. See our Terms & Conditions here.