Safety in electrical installations today is essential, whether at home, work, or in industrial settings. One of the most critical pieces of equipment for ensuring circuit protection is the RCBO
An RCBO is a double-purpose device: A RCBO is both an earth leak detector and a short circuit and overload protector, like an RCD and an MCB.The device prevents electrical fires and electric shocks effectively and economically.
Due to all the different RCBO types and growing concerns about arc faults and leakage currents, many people are wondering: Which RCBO should I use?
The following is a guide to RCBO types, how they work, and how to choose the right device for safer and code-compliant installations.
What Are Arc Faults and Earth Leakages?
Before we explore the types of RCBO, let’s find out what they protect against.
Arc Faults
An arc fault occurs when there is an unintentional release of electricity between two conductors. When such a release occurs, high heat is generated, which is sufficient to burn surrounding objects and cause a fire to break out. Some reasons for arc faults include:
- Damaged wires or insulation
- Loose connections to outlets or switches
- Pressed or bent cables
- Outdated electrical wiring
It is likely that conventional overcurrent protection devices such as MCBs may not detect this type of fault, unless they are equipped with a special arc fault detection device.
Earth Leakages
Earth leakage refers to a current flowing from a live conductor to the earth (ground), causing an electrical short circuit. It may be caused by:
- Insulation failure
- Water seepage
- Direct contact with live wires
Small leakage currents (generally greater than 30 mA) may result in an electric shock or equipment malfunction. So it is crucial to detect earth leakage for the safety of individuals and system integrity at an early stage.
Overview of RCBO Functionalities
An RCBO combines the functions of two important safety devices into one unit:
- RCD (Residual Current Device): Detects earth leakage currents by monitoring the balance between live and neutral current conductors.
- MCB (Miniature Circuit Breaker): When overcurrent caused by overload or short circuit is detected, a trip is triggered.
RCBO trips automatically when a current unbalance or an overcurrent is detected. Having dual protection makes it the perfect solution for protecting individual circuits from both fire and shock.
Compared to RCDs for multiple circuits, RCBOs are usually installed separately for each circuit. This helps improve fault isolation and reduces interference with power supply when tripping occurs.
Different Types and Functions of RCBOs
Different types of RCBOs can detect specific types of residual current. Select the appropriate type based on specific requirements to provide adequate protection for high-risk or sensitive applications.
RCBOs come in different types, each designed to detect specific forms of residual current. Choosing the right type ensures that sensitive or high-risk applications are adequately protected.
Type AC RCBO
- Detection: AC sinusoidal residual currents alone.
- Application: Basic domestic loads such as lighting circuits or old appliances.
- Shortcoming: Does not identify DC content, so it cannot be applied to new electronics.
Type A RCBO
- Detection: AC + pulsating direct current (DC) residual currents.
- Application: Suitable for circuits containing electronic equipment, such as induction hobs, dimmers, or washing machines.
- Advantage: Provides greater protection than Type AC and is currently a universal requirement in the majority of modern homes.
Type B RCBO
- Detection: AC, pulsating DC, and smooth DC residual currents.
- Application: Electric vehicle (EV) charging units, solar photovoltaic systems, and variable frequency drives (VFDs).
- Advantage: Offers the broadest protection, especially for equipment with complex electrical signatures.
Type F RCBO (optional/specialized)
- Detection: High-frequency leakage currents, in addition to what is detected by Type A.
- Application: Medical equipment, power tools, and equipment with variable-speed motors.
Type S RCBO (Selective RCBO)
- Feature: Delayed tripping in order to coordinate with upstream protection measures.
- Application: Cascade protection systems to avoid nuisance tripping on critical circuits.
Comparison Table: RCBO Types at a Glance
| RCBO Type | Detects | Typical Applications | Arc Fault Protection? |
| Type AC | AC only | General lighting, simple outlets | ❌ No |
| Type A | AC + Pulsating DC | Residential electronics, appliances | ❌ No |
| Type B | AC + Pulsating + Smooth DC | EV chargers, PV systems, VFDs | ❌ or ✅ (if integrated) |
| Type F | AC + High-frequency leakage | Motors, medical equipment | ❌ No |
| Type S | Time-delayed protection | Selective coordination in cascades | ❌ No |
Can All RCBOs Types Protect Against Arc Faults?
There’s a common misconception. The standard RCBO does not detect arc faults. In general, they are designed to prevent overcurrents and residual currents (earth leakage), but they are not designed to prevent arcing.
For detection of arc faults, an Arc Fault Detection Device (AFDD) is needed. Some newer circuit breakers now actually integrate RCBO and AFDD functions into a single unit.These hybrid units provide comprehensive protection against:
- Series and parallel arc faults
- Earth leakage
- Short circuits and overloads
They are suited for:
- High-risk areas (e.g. children’s bedrooms, wooden buildings)
- Commercial premises with sensitive loads
- Domestic properties where extended fire protection is desired
Since RCBOs do not actually detect arc faults, they can be used in conjunction with or included in AFDD+RCBO systems to ensure full-spectrum protection.
Select the Appropriate RCBO Type to Achieve Arc and Leakage Protection.
Choosing the right RCBO depends upon the type of installation, load connected, and degree of regulation.
Residential Installations
- Best: Type A RCBO as new standard.
- Alternative: Type B for solar panels or EV chargers.
- Tip: Choose miniature RCBOs with clear labeling for easy installation.
Commercial & Office Spaces
- Recommended: Type A for typical circuits and Type B when sensitive electronics or DC equipment is present.
- Best Practice: Fit one RCBO per circuit to make fault isolation easier.
Industrial Applications
- Recommended: Type B RCBOs are recommended for VFDs, motor controllers, or renewable energy inputs.
- Note: Adhere to local codes and IEC 61009 standards.
EV Charging Installations
- Required: Type B RCBO or a Type A RCBO + 6mA DC detection module.
- Reason: EV chargers can leak smooth DC current, which Type A cannot detect.
Final Thoughts
RCBOs play a significant role in electrical security. They avoid fires, reduce electric shock risks, and offer circuit-specific protection. However, one needs to:
- Guarantee that the RCBO type matches the equipment and installation conditions.
- Be aware of limitations: Ordinary RCBOs will not identify arc faults unless incorporated with an AFDD.
- Adhere to local codes: Check if Type B or AFDDs are necessary in your area all the time.
Taking higher-grade protection is not simply a technical decision. It is a safety requirement when working with newer electrical equipment, particularly those involving power electronics, renewable energy sources, or integrating electric vehicles.
As you evaluate protection devices for your installation, it’s also important to choose products from reputable manufacturers. Melvolt is a well-known brand in the electrical component industry for producing high-quality isolator switches, RCBOs, surge protection devices, and other electrical components. The safety, durability, and performance of Melvolt products are widely relied upon across residential, commercial, and industrial settings.
FAQs
What’s the difference between an RCBO and an AFDD?
An RCBO protects against two main hazards: earth leakage (residual current) and overcurrent (overload and short circuit).In this way, the circuit is protected from electric shock and fire risks by automatically shutting down when dangerous current conditions are present.
An AFDD (Arc Fault Detection Device), on the other hand, is designed specifically to detect arc faults, which are high-risk electrical discharges caused by damaged or deteriorated wiring. These arcs often do not produce enough current to trip an RCBO or MCB, making AFDDs essential for detecting early fire risks.
For full spectrum protection, some modern protection devices combine both RCBOs and AFDDs into one unit.
Can I use an RCBO with older electrical equipment or systems?
Yes, but with caution.The RCBO is generally backward compatible, however it is sensitive to current imbalances, so older appliances with leaky insulation or strong inrush currents may trip the RCBO without warning.
When retrofitting older systems:
- Choose the correct RCBO type (Type A or B) based on the type of load.
- Consider the installation’s grounding system and cable condition.
- If using multiple RCBOs in a shared neutral configuration, ensure proper wiring to avoid false trips.
In general, the use of RCBOs improves protection even in legacy systems, but they must be installed and tested correctly in order to be reliable.
