Arc Fault Detection Devices (AFDDs) represent a significant advancement in electrical fire safety. This whitepaper provides a comprehensive technical analysis of AFDD requirements under BS 7671:2018+A2:2022, their operational principles, implementation challenges, and specific product solutions from leading manufacturers Hager and Schneider Electric. The document addresses the ongoing debate regarding AFDD effectiveness in ring final circuits and provides guidance for electrical professionals on risk assessment, selection, and installation.

1. Regulatory Framework

1.1 Evolution of AFDD Requirements in UK Standards

The UK’s approach to Arc Fault Detection Devices is defined through the IET Wiring Regulations BS 7671:2018+A2:2022, which represents the national standard for electrical installations. The inclusion of AFDDs reflects the industry’s commitment to enhancing fire safety through technological innovation.

Amendment 2 to the 18th Edition introduced significant changes to the recommendations for AFDD implementation. Specifically, Regulation 421.1.7 states:

“In order to provide protection against fire, an arc fault detection device (AFDD) conforming to BS EN 62606 shall be provided for single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32 A in:

(i) higher risk residential buildings
(ii) houses of multiple occupation (HMOs)
(iii) purpose-built student accommodation
(iv) care homes.”

This regulation represents a shift from the previous edition, where AFDDs were only recommended for consideration in certain locations. The current wording establishes a clearer requirement for AFDD installation in specific high-risk environments.

1.2 Relationship with European Standards

AFDDs in the UK must conform to BS EN 62606, which provides the product standard for these devices. This standard defines:

Detection requirements for both series and parallel arc faults
Testing methodologies to verify AFDD performance
Operational parameters and reliability requirements
Immunity to unwanted tripping

The alignment with European standards ensures that AFDDs installed in the UK meet internationally recognized safety criteria while addressing the specific requirements of UK electrical installations.

2. Technical Principles and Operation

2.1 Arc Fault Detection Mechanisms

AFDDs employ microprocessor technology to analyse electrical waveforms and identify the distinctive signatures of dangerous arcs. These devices continuously monitor the electrical circuit for the following conditions:

High-frequency noise patterns indicative of arcing
Current waveform distortions
Rapid changes in current magnitude
Specific frequency components associated with arc faults

When an arc fault is detected, the AFDD automatically disconnects the circuit, preventing the arc from reaching temperatures that could ignite surrounding materials.

2.2 Types of Arc Faults Detected

AFDDs are designed to detect two primary types of arc faults:

Series Arc Faults: These occur when current flows through an unintended break in a conductor. Common causes include damaged cables, loose connections, or broken conductor strands. Series arcs occur in line with the load and may not draw sufficient current to trigger conventional overcurrent protection.

Parallel Arc Faults: These occur between live conductors (line-to-line) or between a live conductor and earth. Parallel arcs typically draw higher currents and may trigger conventional overcurrent protection if the fault current exceeds the trip threshold.

2.3 Differentiation from Other Protective Devices

It is essential to understand that AFDDs complement rather than replace other protective devices:

Miniature Circuit Breakers (MCBs): Provide protection against overloads and short circuits, but cannot detect low-current arcing faults.
Residual Current Devices (RCDs): Detect earth leakage currents but cannot identify arcing between line conductors or series arcs.
Residual Current Circuit Breakers with Overcurrent Protection (RCBOs): Combine RCD and MCB functions but lack specific capabilities for detecting arc faults.
RCBO with Arc Fault Detection (RCBO-AFDD): Integrated devices that combine overcurrent protection, residual current protection, and arc fault detection in a single module.

AAFDDs address a protection gap in conventional systems by detecting dangerous arcing conditions that may not trigger other protective devices. When combined with RCBO functionality in a single unit (RCBO-AFDD), they offer the most comprehensive protection solution available for electrical circuits.

3. Application Requirements in BS 7671:2018+A2:2022

3.1 Mandatory vs. Recommended Use

Under BS 7671:2018+A2:2022, AFDDs are required for single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32 A in specific high-risk environments. However, Regulation 421.1.7 also includes a broader recommendation to consider AFDD installation in:

Premises with sleeping accommodation
Locations with combustible construction materials
Fire propagation structures (buildings with risk of fire spread)
Premises with irreplaceable goods or high-value assets

The regulation places responsibility on the designer to assess risk and determine whether AFDDs are necessary beyond the mandatory applications.

3.2 Circuit Types and Ratings

The focus on socket-outlet circuits not exceeding 32 A aligns with the typical rating used in UK domestic and commercial installations. This encompasses:

Standard 20 A radial circuits
32 A radial circuits
Ring final circuits (typically protected at 32 A)

The emphasis on these circuits reflects their prevalence in areas where people sleep and where electrical fires may pose the greatest risk to life safety.

3.3 Installation Location Requirements

BS 7671 specifies that AFDDs should be installed at the origin of the final circuit in a consumer unit or distribution board. This positioning ensures that the entire circuit, including the fixed wiring, is protected against arc faults.

4. AFDD Application in Ring Final Circuits

4.1 Technical Considerations for Ring Circuits

The application of AFDDs on ring final circuits presents specific technical considerations. Ring circuits, which are common in UK installations, create a unique electrical environment that affects AFDD operation.

According to NICEIC guidance, AFDDs are effective at detecting parallel arcing faults in ring circuits but may have limitations in detecting series arcing faults in ring configuration. This is due to the dual-path nature of ring circuits, where current can flow through either side of the ring to any connected load.

4.2 Current Industry Guidance

The debate regarding AFDD effectiveness on ring circuits highlights the importance of:

Continuous testing and inspection to ensure circuit integrity
Proper installation and maintenance of ring circuits
Consideration of alternative circuit designs in high-risk areas
Manufacturer-specific guidance for AFDD application on ring circuits

Electrical designers should consult with AFDD manufacturers regarding the suitability of specific devices for ring circuit applications and consider the overall risk assessment when determining protection strategies.

5. Specific AFDD Products for UK Applications

5.1 Hager AFDD Solutions

Hager offers a comprehensive range of AFDD solutions specifically designed for the UK market and compliant with BS 7671:2018+A2:2022 requirements. Their product lineup includes both standalone AFDD-MCB combinations and integrated RCBO-AFDD devices:

5.1.1 Hager 20A AFDD Solutions

ARM920U: 20A single module AFDD MCB with B curve characteristics. Key features include:

Single module (18mm) width for space efficiency in consumer units
6kA breaking capacity to BS EN 60898
B curve tripping characteristics suitable for general purpose and resistive loads
Integrated diagnostic LED for fault indication
Compliance with BS EN 62606 for arc fault detection

ARL920U: 20A single module RCBO with AFDD protection, offering comprehensive protection in a single device:

Combined RCBO and AFDD functionality (overcurrent, residual current, and arc fault protection)
6kA breaking capacity to BS EN 60898
B curve tripping characteristics
Type A 30mA residual current protection
Single module (18mm) width design
1m lead-free lead (LFL) for flexible installation
Integrated diagnostic LED for fault identification
Compliance with BS EN 62606 for arc fault detection

5.1.2 Hager 32A AFDD Solutions

Hager offers multiple 32A AFDD solutions:

ARM932U: 32A single module AFDD MCB with B curve characteristics, featuring:

Single module design (18mm width)
6kA breaking capacity
B curve tripping characteristics
Integrated diagnostic LED
BS EN 62606 compliance

ARM982U: 32A single module AFDD MCB with C curve characteristics, offering:

Enhanced immunity to surge currents for motor loads and higher inrush equipment
6kA breaking capacity
C curve tripping characteristics
Single module design
Integrated diagnostic LED

ARL932U: 32A single module RCBO with AFDD protection, providing:

Integrated overcurrent, residual current, and arc fault protection
6kA breaking capacity
B curve tripping characteristics
Type A 30mA residual current protection
Single module design
Diagnostic LED for fault identification

All models provide comprehensive protection against series and parallel arc faults while maintaining compatibility with standard Hager consumer units. The RCBO-AFDD models (ARL series) offer the most complete protection solution in a space-efficient single module format.

5.2 Schneider Electric AFDD Solutions

Schneider Electric’s Acti9 range includes advanced AFDD solutions designed for the UK market and compliant with BS 7671:2018+A2:2022.

5.2.1 Schneider Electric 20A AFDD Solutions

The A9TDFD620 is Schneider’s 20A Active Arc Fault Detection RCBO, featuring:

Combined AFDD, MCB, and RCD functionality in a single device
1P+N configuration with C curve characteristics
30mA Type A-SI residual current protection
10kA breaking capacity
All-in-one protection in a simplified and compact form
Diagnostic LED for easy fault identification
Spring terminals to reduce wiring time

5.2.2 Schneider Electric 32A AFDDs

The A9TDFD632 is Schneider’s 32A Active Arc Fault Detection RCBO, offering:

Integrated AFDD, MCB, and RCD protection
1P+N configuration with C curve characteristics
30mA Type A-SI residual current protection
10kA breaking capacity
Compact design for consumer unit installation
Diagnostic LED system
Markable cable ends to facilitate installation

Both Schneider Electric models provide comprehensive protection against electrical faults, including arc faults, overcurrents, and earth leakage in a single device.

6. Design and Installation Considerations

6.1 Consumer Unit Integration

When integrating AFDDs into consumer units, designers and installers should consider:

Space requirements: AFDDs may require additional module space compared to standard MCBs
Compatibility with existing consumer unit designs
Heat dissipation within the enclosure
Accessibility for testing and maintenance
Clear labeling of AFDD-protected circuits

Both Hager and Schneider Electric offer AFDD solutions designed for seamless integration with their respective consumer unit ranges.

6.2 Coordination with Other Protective Devices

AFDDs must be coordinated with other protective devices to ensure effective operation:

Selectivity with upstream protection
Coordination with RCDs for comprehensive fault protection
Integration with surge protection devices (SPDs)
Consideration of backup protection requirements

Manufacturers’ technical documentation should be consulted to ensure proper coordination between protective devices.

6.3 Testing and Verification

BS 7671 requires that AFDDs, where installed, be recorded in the electrical installation certificate and inspected according to Part 6 of the regulations. Verification should include:

Functional testing using the test button
Visual inspection for damage or incorrect installation
Verification of correct rating and type
Documentation in installation schedules
Inclusion in operation and maintenance manuals

Regular testing of AFDDs is essential to ensure continued protection against arc faults.

7. Risk Assessment and Decision-Making

7.1 Identifying High-Risk Applications

Electrical designers should conduct a thorough risk assessment to identify applications where AFDDs provide significant safety benefits. Factors to consider include:

Presence of sleeping accommodation
Building construction materials and fire propagation risk
Value and replaceability of assets
Occupant vulnerability (elderly, children, disabled persons)
Historical data on electrical fire incidents
Circuit loading patterns and equipment types

The risk assessment should be documented to support design decisions regarding AFDD implementation.

7.2 Cost-Benefit Analysis

While AFDDs represent an additional cost compared to standard protective devices, their benefits must be evaluated in the context of:

Life safety improvements
Property protection value
Insurance implications
Regulatory compliance
Reputation and liability considerations

The relatively recent introduction of AFDDs to the UK market means they command a premium price and require additional consumer unit space. However, these factors must be balanced against the potential cost of electrical fires and the value of enhanced safety.

7.3 Early Design Consideration

It is imperative to identify AFDD requirements during the preliminary design stage to avoid complications later in the project. Early consideration allows for:

Appropriate consumer unit specification
Adequate space allocation
Proper circuit design and load distribution
Budget allocation for enhanced protection
Client education regarding AFDD benefits

Failing to identify AFDD requirements early can lead to significant redesign costs and project delays.

8. Practical Implementation Challenges

8.1 Potential Arcing Causes

Understanding the common causes of arc faults helps in designing installations that minimise risk:

Cable entrapment or compression during installation
Compromised insulation due to physical damage
Damage from rodents or other pests
Insecure connections in accessories or equipment
Insulation degradation due to aging or environmental factors

Installation practices should aim to minimize these risks while AFDDs provide protection against faults that do occur.

8.2 Unwanted Tripping Considerations

Modern AFDDs are designed to minimize unwanted tripping, but certain loads may present challenges:

Brush motors with normal operational arcing
Certain electronic equipment with high-frequency components
Dimmer switches and speed controllers
Older appliances with less sophisticated interference suppression

Both Hager and Schneider Electric AFDDs incorporate advanced algorithms to differentiate between dangerous arcs and normal operational arcing, reducing the likelihood of unwanted tripping.

8.3 Retrofit Considerations

When retrofitting AFDDs to existing installations, additional considerations include:

Condition assessment of existing wiring
Space constraints in existing consumer units
Potential need for consumer unit replacement
Circuit identification and load assessment
Client education regarding new protection features

Retrofit installations may require more extensive survey and preparation work compared to new installations.

9. Future Developments

9.1 Evolving Standards

The requirements for AFDDs in UK electrical installations are likely to evolve with future amendments to BS 7671. Potential developments include:

Expansion of mandatory applications
Enhanced testing requirements
Integration with smart building systems
Improved discrimination and coordination specifications

Electrical professionals should maintain awareness of regulatory developments affecting AFDD requirements.

9.2 Technological Advancements

AFDD technology continues to advance, with potential future developments including:

Enhanced discrimination between dangerous and normal arcing
Reduced physical size
Integration with energy monitoring and management systems
Remote monitoring and notification capabilities
Improved diagnostic information

Both Hager and Schneider Electric, and many others, continue to invest in AFDD technology development to enhance safety and functionality.

10. TL;DR

Arc Fault Detection Devices represent an important advancement in electrical fire safety within UK installations. Although using them in ring final circuits has some technical challenges, the safety they offer against harmful arc faults fills a major gap in traditional protection systems.

BS 7671:2018+A2:2022 establishes clear requirements for AFDD installation in high-risk environments, with broader recommendations for consideration in other applications. Electrical designers and installers must understand these requirements and the technical principles of AFDD operation to implement effective protection strategies.

Both Hager and Schneider Electric offer AFDD solutions specifically designed for the UK market, with models available in the critical 20A and 32A ratings required for compliance with BS 7671. These devices provide comprehensive protection against arc faults while integrating with existing Distribution Systems.

Through proper risk assessment, early design consideration, and appropriate product selection, electrical professionals can enhance fire safety in UK installations and provide clients with state-of-the-art protection against arc fault hazards.

References

The Institution of Engineering and Technology. (2022). BS 7671:2018+A2:2022 Requirements for Electrical Installations. IET Wiring Regulations 18th Edition. IET.
BEAMA. (2022). Guide to Arc Fault Detection Devices (AFDDs). BEAMA Ltd.
NICEIC. (2022 ). Technical Guidance on Arc Fault Detection Devices. NICEIC Group Limited.
British Standards Institution. (2014). BS EN 62606:2013+A1:2017 General requirements for arc fault detection devices. BSI.
Hager Ltd. (2023). Arc fault detection devices (AFDD).
Hager Ltd. (2023 ). ARM920U MCB with dangerous arc detection 1M 20A B curve 6kA. Technical Datasheet.
Hager Ltd. (2023 ). ARM932U MCB with dangerous arc detection 1M 32A B curve 6kA. Technical Datasheet.
Hager Ltd. (2023 ). ARM982U MCB with dangerous arc detection 1M 32A C curve 6kA. Technical Datasheet.
Hager Ltd. (2023 ). ARL920U RCBO with dangerous arc detection 1M 20A B 6kA A 30mA LFL 1m. Technical Datasheet.
Hager Ltd. (2023 ). ARL932U RCBO with dangerous arc detection 1M 32A B 6kA A 30mA LFL 1m. Technical Datasheet.
Schneider Electric UK. (2023 ). Acti9 Arc Fault Detection Devices – AFDD.
Schneider Electric UK. (2023 ). A9TDFD620 – Active arc fault detection RCBO, Acti9 iCV40H ARC, 1P + N, 20 A, C curve, 30 mA, type A-SI, 10000 A. Technical Datasheet.
Schneider Electric UK. (2023 ). A9TDFD632 – Active arc fault detection RCBO, Acti9 iCV40H ARC, 1P + N, 32 A, C curve, 30 mA, type A-SI, 10000 A. Technical Datasheet.
Professional Electrician. (2022, June 14 ). Amendment 2: Arc Fault Detection Device (AFDD) requirements.
Electrical Safety UK. (2023 ). Arc Fault Detection Devices (AFDDs).
The Institution of Engineering and Technology. (2022 ). 18th Edition changes.
BEAMA. (2022 ). What’s new for Arc Fault Detection Devices (AFDDs) in BS 7671 Amendment 2.
Electrical 4 Less. (2023 ). AFDD – Arc Fault Detection Devices.
Electrical2Go. (2023 ). Guide to Arc Fault Detection Devices – AFDDs.
TLC Electrical Supplies. (2023 ). AFDD Arc Fault Detection Device – Hager.
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