RCBOs

RCBOs are Residual Current Circuit Breaker with Overcurrent protection. It is a vital electrical safety device unit that combines the functions of an RCD (Residual Current Device) and MCB (Miniature Circuit Breaker). Find out more in our comprehensive RCBOs guide.

RCBOs are designed to provide protection against two primary types of electrical hazards: overcurrents (caused by overloads or short circuits) and earth leakage currents. They operate by continuously monitoring the current flowing through a circuit. If an imbalance is detected (indicating an earth leakage fault), or if the current exceeds safe limits, the RCBO will quickly disconnect the circuit.

How do RCBOs Work?

An RCBO contains a sophisticated mechanism that integrates both magnetic and thermal tripping elements for overcurrent protection alongside a sensitive coil for earth leakage detection.

When an overload occurs (e.g. too many appliances plugged into one outlet), the RCBO's thermal element heats up. As the bimetallic strip inside the RCBO heats, it bends, eventually tripping the mechanical latch and breaking the circuit.

In the event of a short circuit due to a direct connection between live and neutral (or live and earth) conductors, the RCBO's magnetic element comes into play. A coil inside the RCBO generates a strong magnetic field from this sudden surge in current, which rapidly activates a plunger to trip the mechanism and provide almost instantaneous protection.

For earth leakage protection, the RCBO's residual current detection coil continuously monitors the balance of current flowing through the live and neutral conductors. In a healthy circuit, the current flowing out through the live wire should exactly equal the current returning through the neutral wire. If a fault occurs (e.g. a person touches a live wire, or current leaks to earth through damaged insulation), this balance is disturbed. Even a small imbalance, typically as low as 30mA for personnel protection, will cause the differential current to induce a magnetic field in the sensing coil. This field then activates a tripping mechanism, safely disconnecting the power within milliseconds.

The rapid reaction time and near-instantaneous response of an RCBO is critical for preventing overheating, electrical infrastructure damage, and serious electric shocks.

Applications of RCBOs

RCBOs are available in a large range of different breaking capacities and tripping characteristics. This makes them highly versatile across applications from industrial fields to home appliances. Some specific applications where RCBOs are commonly employed include:

• Residential: RCBOs often feature in dedicated and final sub-circuits for kitchens (where appliances like ovens and dishwashers are present), bathrooms (due to the presence of water and electrical appliances), and outdoor power outlets (where exposure to moisture or damage is higher). By providing combined protection at the circuit level, RCBOs minimise the risk of electric shock and fire hazards, making homes safer for occupants.
• Commercial: In commercial environments such as offices, retail outlets, and restaurants, RCBOs are used to protect lighting circuits, power outlets for computers and electronic equipment, and circuits supplying kitchenettes or staff rooms. Their ability to protect against both overcurrents and earth faults helps maintain business continuity by preventing widespread power outages caused by a single circuit fault.
• Industrial: In industrial settings, RCBOs are critical for protecting sophisticated machinery, motor control panels, and automation systems. Industrial RCBOs with specific tripping characteristics can be chosen to handle the inrush currents of large motors while still providing sensitive earth fault protection. This helps to protect expensive equipment and ensure the safety of operators.
• Temporary Power Supplies: RCBOs are indispensable in construction sites or temporary outdoor events in Australia, where electrical installations might be more vulnerable to damage or environmental factors. They provide essential safety for workers and the public by quickly reacting to faults in challenging conditions.
• Specialised Circuits: Any circuit where combined protection for personnel and equipment is critical benefits from an RCBO. This might include circuits for sensitive medical equipment, data centres, or even entertainment lighting rigs, where uninterrupted power and absolute safety are paramount.

Types of RCBOs

Understanding the different variation of RCBOs is key to choosing the correct unit for your application. RCBOs can be categorised and grouped according to:

Number of Poles

• Single Pole + Neutral (1P+N): These are the most common type for single phase circuits, often found in residential RCBOs. They provide protection for one active conductor and include a switching neutral.
• Two Pole (2P): These provide protection for both active and neutral conductors and are used in circuits where both poles need to be switched.
• Three Phase (3P)/Three Phase (3P+N): A three phase RCBO provides comprehensive protection for all active conductors in a three phase electrical systems, and may or may not include a switched neutral, depending on the specific model and application. These are crucial for industrial machinery and commercial installations with high-power requirements.

Tripping Characteristics (Curve Types)

Curve types define how quickly an RCBO breaker will trip in response to an overcurrent. Common curves include:

• B-Curve: Designed to trip rapidly when the current reaches 3 to 5 times its rated current. These are ideal for circuits with resistive loads, such as residential lighting and heating, where minor surges are not expected.
• C-Curve: The most common curve for general commercial and industrial applications in Australia that trips when the current reaches 5 to 10 times its rated current. They can tolerate higher inrush currents from inductive loads like motors, fluorescent lighting, and transformers without nuisance tripping.
• D-Curve: A D-Curve RCBO is engineered to trip at 10 to 20 times its rated current. They provide the highest level of inrush current tolerance, ideal for highly inductive loads such as welding machines, X-ray machines, and large motor circuits.

Residual Current Detection Type

• Type AC RCBO: Designed to detect sinusoidal AC earth leakage currents only. This is the most basic type and is suitable for general-purpose AC loads without electronic components.
• Type A RCBO: This is a more advanced RCBO that detects both sinusoidal AC and pulsating DC earth leakage currents.They are widely recommended for modern installations as they provide protection for circuits containing electronic equipment with rectifiers such as computers, washing machines, and LED lighting, which can produce pulsating DC fault currents.
• Type F RCBO: Designed for circuits with variable speed drives (VSDs) or other single-phase loads with frequency converters, which can produce mixed-frequency fault currents.
• Type B RCBO: Provides the highest level of protection capable of detecting smooth DC earth leakage currents, in addition to AC and pulsating DC. Type B RCBOs are essential for applications involving electric vehicle charging stations, solar PV systems, and some medical equipment, where pure DC fault currents can occur.

How to Install RCBOs

Per the Australian and New Zealand Wiring Rules (AS/NZS 3000) and local building regulation, an RCBO must always be installed by a licensed electrician to ensure safety and compliance. While a comprehensive guide to installation is beyond our scope, general guidance includes:

• Safety First: Always ensure the main power supply to the consumer unit or switchboard is completely isolated and locked out before commencing any work.
• Mounting: RCBOs are typically mounted on a DIN rail within the electrical switchboard.
• Wiring: Connect the live and neutral conductors of the circuit to the designated terminals on the RCBO. Ensure all connections are secure and tight to prevent loose contacts and overheating.
• Testing: After installation and before re-energising the circuit, a licensed electrician must perform mandatory tests. This includes operating the test button on the RCBO at least twice to verify its residual current device function. Further testing using specialised equipment is also required to confirm correct wiring and tripping characteristics in accordance with AS/NZS 3000.
• Documentation: Record the installation details and test results as per Australian electrical safety requirements.

How to Choose the Right RCBOs

Selecting the correct RCBO for a project or application in Australia is critical for ensuring effective protection and avoiding nuisance tripping. Here are some useful tips and guidelines:

1. Assess the Electrical Load: Determine the total current draw of the circuit the RCBO will protect. This will dictate the appropriate current rating (e.g., 10A, 16A, 20A, 32A). For continuous loads, it's often recommended to choose an RCBO rated at 125% of the continuous load.
2. Identify Load Characteristics: Consider the nature of the electrical loads on the circuit. If the circuit will supply motors, transformers, or other devices with high inrush currents, a C-Curve or D-Curve RCBO might be more suitable to prevent nuisance tripping upon startup. For purely resistive loads, a B-Curve might suffice.
3. Determine Earth Fault Sensitivity: For general protection of people against electric shock, a 30mA earth leakage trip current is typically required for final sub-circuits in Australia. For specific applications like medical equipment or construction sites, lower sensitivities (e.g. 10mA) might be necessary.
4. Consider Earth Leakage Type: With the increasing use of electronic devices, Type A RCBOs are becoming the standard for residential and most commercial applications in Australia as they detect both AC and pulsating DC leakage currents. For highly sensitive equipment or DC loads, Type B RCBOs might be required.
5. Verify Breaking Capacity: Ensure the RCBO circuit breaker has a sufficient breaking capacity (kA rating) to safely interrupt the maximum fault current that could occur at its point of installation. This is crucial for safely handling short circuits.
6. Compliance with Australian Standards: Always ensure the RCBO chosen complies with relevant regulations and standards, particularly AS/NZS 61009.1. Look for regulatory compliance marks or consult a trained electrician.
7. Physical Size and Mounting: Check the physical dimensions of the RCBO unit to ensure it fits within the existing switchboard or enclosure, especially for compact or single-module RCBOs.

Buy RCBOs Online from RS Australia

When you need to buy RCBOs for your next electrical project, RS Australia has got your back. As a leading RCBO supplier and distributor, we offer a comprehensive RCBO selection suitable for industrial, commercial, and residential applications. Renowned manufacturers like Hager, Clipsal Electrical, Schneider Electric, and ABB can be found on our online shopping platform, bringing you top-quality equipment at competitive prices.

Ordering RCBO units from RS is simple and straightforward. Simply search for the specific RCBO you need, add it to your basket, and proceed to online checkout. Business account customers, you can also utilise quick order functions by entering RS stock numbers or setting up parts lists for frequently purchased items. We also accept orders via phone, email, or fax for your convenience. Find out more about our nationwide doorstep delivery on our Delivery Page.