How to Choose an RCBO? Understanding Type A RCBO and Type B RCBO

Selecting the correct RCBO is not simply about choosing the right current rating. Modern electrical installations often contain electronic equipment, inverters, EV chargers, variable-speed drives, and switch-mode power supplies that can generate different types of residual current.

An RCBO installed in a modern distribution board protecting electronic loads

An RCBO provides both residual-current protection and overcurrent protection in a single device. However, choosing the wrong RCBO type may reduce protection effectiveness and lead to nuisance tripping or failure to detect certain fault conditions.

That is why understanding the difference between Type A RCBO and Type B RCBO is essential when designing or upgrading electrical systems.

Why RCBO Type Matters

Many installers focus on:

• Rated current
• Breaking capacity
• Number of poles
• Tripping characteristics

While these specifications are important, the residual-current type is equally critical.

Different electrical loads can produce different leakage-current waveforms. Not every RCBO is designed to detect all of them.

Technical illustration showing AC, pulsating DC, and smooth DC residual current waveforms

If the wrong RCBO type is selected, dangerous earth-fault currents may not be detected correctly.

What Is a Type A RCBO?

A Type A RCBO is designed to detect:

• Alternating sinusoidal residual currents (AC)
• Pulsating DC residual currents

This makes Type A devices suitable for most modern residential and commercial installations where electronic equipment is present.

Typical Applications for Type A RCBO

Type A RCBOs are commonly used for:

• Residential distribution boards
• Socket outlet circuits
• Lighting circuits
• Washing machines
• Dishwashers
• Air conditioners
• Computers and office equipment
• Electronic power supplies

Because many modern appliances contain electronic components and rectifiers, Type A RCBOs are increasingly preferred over older Type AC devices.

Type A RCBO Detection Capability

For most standard residential and commercial applications, Type A RCBO provides sufficient protection.

What Is a Type B RCBO?

A Type B RCBO is designed to detect:

• AC residual currents
• Pulsating DC residual currents
• Smooth DC residual currents
• Mixed-frequency residual currents

Type B devices provide the broadest residual-current detection capability among common RCBO types.

Technical diagram illustrating Type B RCBO detection across multiple residual-current waveforms

This makes them suitable for installations where DC fault currents may be generated.

Typical Applications for Type B RCBO

Type B RCBOs are commonly used in:

• EV charging stations
• Solar photovoltaic systems
• Battery energy storage systems
• Variable frequency drives (VFDs)
• Industrial automation equipment
• Three-phase inverter systems
• UPS systems
• Medical equipment installations

These applications can generate smooth DC residual currents that may blind or saturate conventional Type A devices.

Type B RCBO Detection Capability

Because of its broader detection range, Type B RCBO is often specified for advanced electrical systems.

Type A RCBO vs Type B RCBO

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This is the most important comparison when selecting an RCBO.

Comparison Table

Key Difference

The main difference is the ability to detect smooth DC residual currents.

A Type A RCBO may not operate correctly if significant smooth DC leakage is present.

A Type B RCBO is specifically designed to detect these fault conditions and maintain protection performance.

How to Choose the Right RCBO

Choosing the correct RCBO starts with understanding the connected load.

Step 1: Identify the Application

Ask:

• Is this a standard residential circuit?
• Does the circuit contain electronic equipment?
• Is there an inverter or frequency converter?
• Is EV charging involved?
• Is solar generation connected?

The answers will guide RCBO type selection.

Step 2: Evaluate Leakage Current Characteristics

Different equipment creates different residual-current waveforms.

Step 3: Select the Correct Current Rating

The rated current should match:

• Circuit design current
• Cable capacity
• Load requirements
• Local regulations

Common ratings include:

• 6A
• 10A
• 16A
• 20A
• 32A
• 40A
• 63A

Step 4: Select Residual-Current Sensitivity

Common sensitivity ratings include:

30mA remains the most common choice for final circuits.

Step 5: Verify Breaking Capacity

The RCBO must be able to interrupt the available fault current.

Typical ratings include:

• 6kA
• 10kA
• 16kA

The required value depends on the fault level at the installation point.

Common Selection Mistakes

Many specification and purchasing errors come from misunderstanding RCBO types.

Common mistakes include:

• Selecting Type A for EV charging systems that require Type B protection
• Choosing based only on current rating
• Ignoring residual-current characteristics of connected equipment
• Assuming all RCBOs provide identical protection
• Overlooking future system expansion

The RCBO type should always be selected according to actual load behavior rather than price alone.

Quick Selection Guide

Conclusion

Choosing the correct RCBO involves more than selecting the right current rating. The residual-current type is a critical factor that directly affects protection performance.

For most residential and commercial circuits, a Type A RCBO provides effective protection against AC and pulsating DC residual currents.

For EV chargers, solar installations, battery storage systems, and industrial inverter-driven equipment, a Type B RCBO is often the preferred solution because it can detect smooth DC residual currents and complex fault waveforms.

Understanding the difference between Type A RCBO and Type B RCBO helps ensure compliance, improve safety, and provide reliable protection for modern electrical systems.

RCBO (Residual Current Breaker with Overcurrent) | Safe & Reliable Kuangya

FAQ

Should I use Type A or Type B RCBO?

For standard residential and commercial circuits, Type A RCBO is usually sufficient. For EV chargers, solar inverters, battery storage, and variable-frequency drives, Type B RCBO is generally recommended.

Can a Type A RCBO detect DC leakage?

Type A RCBO can detect pulsating DC residual currents but cannot reliably detect smooth DC residual currents.

Why is Type B RCBO more expensive?

Type B RCBO contains more advanced sensing technology capable of detecting a wider range of residual-current waveforms, including smooth DC faults.

Is Type B RCBO required for EV charging?

Many EV charging applications either require Type B protection or equivalent DC fault detection measures, depending on local standards and charger design.

Can Type B RCBO replace Type A RCBO?

Technically yes, because Type B provides broader protection coverage. However, Type B devices are more expensive and may not be necessary for standard circuits.