Professional note
Device selection, discrimination, and exemption routes are specified in BS 7671 and manufacturer data. Your contractor applies the formal rules to your certificate and risk assessment.
AFDDs: detecting the sparking that starts fires
Arc Fault Detection Devices (AFDDs) monitor waveforms for signatures associated with series and parallel arcing — the small, sustained sparking that can ignite surrounding material long before current rises enough to trip a circuit breaker or blow a fuse. Think damaged flex under furniture, loose screw terminations, or crushed cable in a door frame: the fault current may sit below the magnetic trip threshold of the line’s MCB or RCBO, yet heat still accumulates at the fault site.
An AFDD is designed to recognise that electrical “noise” and disconnect the circuit. It does not replace an RCD for shock protection; it complements overcurrent and earth-leakage protection for fire risk. That is why BS 7671 routes AFDDs towards locations and circuit types where ignition consequences are greatest.
Amendment 4 (2026) and high-risk settings
BS 7671:2018+A4:2026 maintains and clarifies expectations around high-risk life-safety and similar premises: for example certain final circuits supplying socket-outlets in accommodation with sleeping risk, or other categories defined in the Regulations, where AFDD protection is required unless a documented engineering assessment shows omission is acceptable. The detail is in the Standard; the takeaway for property owners is that new work and upgrades in scope must be designed Amendment 4–aware, not to an outdated mental model of “MCB plus RCD and we are done.”
For older Thanet homes — Victorian terraces, 1930s semis, 1970s estates — wiring may be sound for its era but accessories and hidden joints have lived through decades of vibration, DIY alterations, and high modern loads. An AFDD is not a cure for defective installation, but it is the closest thing we have to a seatbelt: it mitigates a class of fault that statistics show matters in real fires. Combined with periodic inspection and sensible loading (see our overloading guide), it is part of a defensible safety strategy.
SPDs: surge protection alongside arc mitigation
Surge Protection Devices (SPDs) limit transient overvoltages from lightning-related events or switching on the network. They do not detect arcing faults; they protect insulation and electronics from voltage spikes. Amendment 4 reinforces the trend towards explicit surge-risk assessment and routine provision of coordinated SPDs on new and upgraded domestic boards where vulnerability or consequence warrants it.
Fire prevention here is indirect but real: stressed insulation and failed power supplies can precede scorching or secondary faults. On sites with PV, battery storage, or EV equipment, coordination between AFDD, SPD, RCBO, and inverter/charger requirements is part of the same integrated design.
Tags: Fire prevention · Amendment 4 · AFDD · SPD · Regulations
Deeper reading
For full technical breakdowns written in the same house style:
Upgrading protection in Thanet?
Ask for RCBO, AFDD, and SPD options matched to your risk profile and the latest Regulations.
Request a quotation