Why an arc can be dangerous
An arc can occur when electricity jumps across a damaged or loose connection. Potential causes include crushed insulation, damaged flexible cables, loose terminals and cables penetrated by fixings. Some arc conditions may not draw enough current to operate an ordinary circuit breaker quickly.
What an AFDD adds
An arc-fault detection device monitors the circuit for patterns associated with hazardous arcing and disconnects the supply when appropriate. It complements, rather than replaces, overcurrent protection, residual current protection and good installation practice.
Where are AFDDs used?
The requirements depend on the type of premises, circuit and risk. Amendment 2 introduced requirements for certain circuits in higher-risk residential premises, with AFDD protection recommended more widely. The electrical designer should assess the installation and explain whether devices are required or recommended.
AFDDs must be compatible with the consumer unit and installed in accordance with the manufacturer’s instructions.
Technical source: IET consumer guidance on AFDDs.