Standard explained
AFDDs (Arc Fault Detection Devices) Explained
An AFDD detects dangerous arcing faults in wiring — a common cause of electrical fires — and disconnects the circuit. BS 7671 recommends them for certain premises.
An arc fault detection device (AFDD) monitors a circuit for the electrical signature of dangerous arcing — for example from damaged cables, loose terminals or worn accessories. Arcing generates intense heat and is a recognised cause of electrical fires. When an AFDD detects a hazardous arc, it disconnects the circuit.
Why AFDDs were introduced
Conventional protective devices (MCBs and RCDs) do not reliably detect series arcing at normal current levels. AFDDs fill that gap, adding fire-risk protection that other devices cannot provide.
Where BS 7671 addresses them
BS 7671 recommends AFDDs for socket-outlet circuits in certain higher-risk premises — for example those with sleeping accommodation, high fire-risk or irreplaceable contents. The requirement is expressed in a way that makes them strongly recommended in those settings.
On an EICR
The absence of AFDDs where they would now be recommended is generally a C3 improvement, not a failure. Fitting them is most cost-effective as part of a board upgrade. See related devices: RCBO protection and surge protection.
Related service
RCD, RCBO & SPD Upgrades
Improved protection through residual-current, overcurrent and surge protective devices.
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Knowledge article
BS 7671 Explained: The Wiring Regulations
BS 7671 — the IET Wiring Regulations — is the national standard for the safety of electrical installations in the UK, currently the 18th Edition.
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Cable Selection and Sizing Explained
Cable selection under BS 7671 balances current-carrying capacity, installation method, grouping, ambient temperature and voltage drop so conductors run safely.
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Distribution Boards and Consumer Units Explained
Distribution boards (and domestic consumer units) house the protective devices that control and protect each circuit — their condition is central to any EICR.
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Earthing Arrangements Explained (TN-S, TN-C-S, TT)
Earthing arrangements (TN-S, TN-C-S/PME and TT) define how an installation connects to earth — central to shock protection and correct disconnection under BS 7671.
Learn moreThis article provides general guidance and distinguishes legislation, British Standards and good practice. It is not legal advice. Always confirm the specific duties applying to your property and tenure.