Introduction to Arc Fault Detection

Arc Fault Detection Devices (AFDDs) are currently recommended as a means of providing additional protection against fire. Regulation 421.1.7 of BS 7671 recommends the installation of AFDDs to mitigate the risk of fire in AC final circuits of a fixed installation, because of arc fault currents.

An arc fault occurs when loose or corroded connections make intermittent contact and cause sparking or arcing between the connections. This translates into heat, which will break down the insulations of the wire and potentially trigger and electrical fire. Such arcs can range in power and vary a great deal in strength and duration.

Arc fault detection devices conforming to BS EN 62606 are recommended as a means of providing additional protection against fire caused by arc faults in AC final circuits. If used, an AFDD shall be placed at the origin of the circuit to be protected.

Current examples of where such devices can be used include:

Premises with sleeping accommodation
Locations with a risk of fire due to the nature of processed or stored materials, i.e., BE2 locations (e.g., barns, wood working shops, stores of combustible materials)
Locations with combustible construction materials, i.e., CA2 locations (e.g. wooden buildings)
Fire propagating structures, i.e. CB2 locations
Locations with endangering of irreplaceable goods

Regulation 532.6 states that, where specified, arc fault detection devices shall be installed

At the origin of the circuit intended to be protected, and
In AC single-phase circuits not exceeding 230V. AFDDs shall comply with BS EN 62606. Coordination of AFDDs with overcurrent protective devices, if necessary, shall take account of the manufacturer’s instructions

In 2022, Amendment 2 of BS 7671 – 18^th Edition – due for publication on 28^th March will now make mandatory requirements for Arc Fault Detection Devices in some AC final circuits for installations for certain types of higher risk residential buildings.