BS 7671 explained: Arc Fault Detection Device (AFDD)

Safety when it comes to electricity is crucial for any building, whether it is for residential, commercial, or industrial purposes. To reduce the possibility of arc faults and prevent electrical fires, the IET Wiring Regulations or the British Standard BS 7671 highlights the importance of using Arc Fault Detection Devices (AFDDs). This article will discuss the importance of AFDDs and how they can promote electrical safety based on the guidelines provided by BS 7671.

Understanding Arc Faults

Arc faults occur when an unintended electrical discharge or arc occurs in a circuit. They can arise due to various factors, including damaged insulation, loose connections, or aging electrical components. Arc faults pose a significant fire hazard as they generate intense heat, which can ignite surrounding combustible materials, leading to potential property damage, injuries, or even loss of life.

The Role of AFDDs

AFDDs are specialized protective devices designed to detect and respond to arc faults promptly. By continuously monitoring electrical waveforms, AFDDs can identify and differentiate between normal electrical activity and the characteristic signatures of arc faults. When an arc fault is detected, the AFDD acts swiftly to interrupt the circuit, preventing further danger and mitigating the risk of fire.

BS 7671 and AFDD Requirements

BS 7671, the British Standard for electrical installations, provides guidelines and regulations for safe electrical practices in the UK. The standard recognizes the importance of AFDDs in enhancing electrical safety, particularly in residential and similar premises where fire safety is a concern. BS 7671 outlines specific requirements for AFDD installation, including the following:

To comply with Regulation 421.1.7, it is necessary to have arc fault detection devices (AFDDs) that meet BS EN 62606 standards installed in single-phase AC circuits that supply socket-outlets rated up to 32 A in:

  • Higher Risk Residential Buildings (HRRB),
  • Houses in Multiple Occupation (HMO),
  • Purpose-built student accommodation, and
  • Care homes.

HRRBs are assumed to be residential buildings over 18 m in height or above six storeys (Regulation 421.1.7 Note 1)

Benefits of AFDDs

Integrating AFDDs into electrical installations offers several benefits, including:

  1. Enhanced Fire Protection: AFDDs significantly reduce the risk of electrical fires by promptly detecting and interrupting arc faults. This helps safeguard life and property, providing occupants with valuable time to evacuate safely.
  2. Improved Safety Compliance: By incorporating AFDDs in line with BS 7671 regulations, electrical installations can meet the required safety standards, ensuring compliance with legal and regulatory requirements.
  3. Early Detection: AFDDs can identify arc faults at their incipient stage, detecting potentially hazardous conditions before they escalate into serious safety concerns. This proactive approach minimizes the chances of fire incidents and associated damages.


AFDDs can be installed in consumer units and distribution boards. It is mandatory for AFDDs to be placed at the starting point of the circuit they are safeguarding.

Please note there will still be a need for overcurrent protection and, where necessary, RCDs.


Arc Fault Detection Devices (AFDDs) play a vital role in mitigating the risks of arc faults and enhancing electrical safety. As outlined by BS 7671, these devices provide an additional layer of protection, complementing other safety measures such as Residual Current Devices (RCDs). By adhering to the requirements set forth by the IET Wiring Regulations, electrical installations can effectively mitigate the dangers associated with arc faults and minimize the potential for devastating electrical fires. Remember, consulting a qualified electrician is crucial for the correct installation and compliance with the standards outlined in BS 7671.