Seasoned sparkies know their craft like the back of their hand. They have the solution to every electrical hiccup that can occur in your home or business, and the right set of tools and gear to get everything up and running. This can be anything from basic cables and wiring to protective devices that shield you and your family from the risks of electrical shock.

What Are Circuit Breakers?

A circuit breaker is an electrical protection device designed to interrupt or break the flow of electricity when it detects an electrical fault, such as an overload or short circuit. They’re essential in protecting homes, businesses and critical infrastructure from major damage and electrical fires, as well as residents and employees from serious physical harm. Without the correct circuit breakers in place, you’re also risking appliances, machinery and electrical equipment from overheating, catching fire, or even exploding. The devices are necessary gear and regulated by current electrical standards or wiring rules set out in the AS/NZ 3000: 2018 standard. 

How They Work

Breakers are installed in your home’s electrical switchboard or panel, where power is delivered from the grid, and distributed throughout the home via a series of circuits. Each circuit is connected to a separate breaker. In the event of an electrical fault such as a power surge within that circuit, the breaker trips and interrupts flow by breaking the electrical connection. Simple designs consist of bi-metallic trip units that overheat, bend and physically disconnect the link between the breaker contacts. More advanced circuit breakers like AFDDs (ARC Fault Detection Devices) use microprocessors to calculate deviations in set parameters that lead to faults and cut the connection within milliseconds to prevent property damage or physical harm. 

Most Common Types 

MCBs

Miniature circuit breakers or MCBs are the most common type found in Australian homes and most businesses. They’re based around manual switches that need to be reset to the ‘ON’ position after detecting faults and tripping the circuit. These breakers are in compact designs, handle lower voltages, and are very sensitive to changes in current flow. They adequately protect residents from surges and short circuits and are mandatory in both older and new housing stock. 

RCDs

Residual current devices or RCDs offer additional protection against electrical shock. They do this by detecting abrupt current changes in the live and neutral wires, usually from physical contact acting as the ground. RCDs constantly monitor for deviations and can cut power flow within a fraction of a second. Changes to wiring rules now mandate that they are required in new and older homes. 

MCCBs

While MCBs are seen in residential and commercial use, protection in areas with higher voltages is done with Moulded Cast Circuit Breakers or MCCBs. These are the mainstay of industrial facilities where they regulate overloads, short circuits, and under-voltage caused by wiring issues, damaged power lines, malfunctioning machinery or transformers, etc. They can handle current of up to 1000 amps and can be remotely operated (unlike MCBs) via shunt wires. 

RCBOs

These are a combination of MCBs and RCDs and protect against electrical shock, overloads, and shorting. They come in the same slim form factor as MCBs so can fit within constrained spaces in switchboards, while not costing much more than standard breakers. The comprehensive protection (ground and overcurrent faults) means they’re preferred in many applications. 
These types of breakers meet current standards, but newer and more efficient products like AFDDs and Ground Fault Circuit Interrupters (GFCIs) are used in areas prone to arc and ground faults, such as kitchens, bathrooms and laundries. Their use is regulated by state laws. 

Choosing Breakers 

Breaker Types

Standard breakers and MCBs are offered in different ‘types’. Homes and areas relying on lower currents benefit from ‘Type B’ breakers that trip if the current flowing through it reaches three to five times its recommended maximum or its ‘rated load. The higher sensitivity is ideal where current surges are small but still lethal and have the potential to damage common household items. ‘Type C’ breakers are more common in commercial and light industrial settings, with the breaker tripping if the current exceeds five to ten times the load. Very high voltage applications (large electrical motors, welding machines, X-ray machines etc) are covered by ‘Type D’ breakers. These trip if the current exceeds ten to twenty times the rated maximum, and ensure an uninterrupted power supply. 

Number of Poles

The number of poles, or the circuits each breaker can protect is another buying consideration. Single pole (also called single-phase) breakers are designed to interrupt the power supply in one live wire, for instance in light switches. Double pole types work in connections with two live wires and a neutral wire, such as bigger household appliances. Three pole variants can break the supply in three separate wires, usually in equipment found in commercial or industrial premises. Lastly, there are four pole protection devices seen in place with an unbalanced power supply, with three phases and a neutral. The difference allows buyers to choose the appropriate breaker for the installation and ensure maximum safety. 

Other Factors 

Choose a breaker with the correct ampere rating for the load. This is the maximum current it can handle before tripping and is stated in Amperes. For most residential uses this is 10 or 20A. Additionally consider breaking capacity, or the maximum amount of current a breaker can interrupt during overloads, surges, and short circuits without enduring damage.