Chapter 42: thermal effectsWhen is an AFDD required?

Chapter 42 is protection against thermal effects — fire, burns, harmful heat, thermal radiation, degradation of materials, propagation of flame and smoke.

421.1.201 — the non-combustible consumer unit

So a plastic consumer unit only qualifies inside a non-combustible cabinet or enclosure. It's a fair bet for a question. Notice too that 421 refers you back to Section 132 in Part 1 — another reminder that the book constantly cross-references itself.

421.1.7 — arc fault detection devices

AFDDs are no longer merely recommended. The regulation says they shall be provided, to BS EN 62606, for single-phase AC final circuits supplying socket-outlets not exceeding 32 A in four kinds of premises: higher-risk residential buildings (residential buildings over 18 m in height or in excess of six storeys, whichever is met first), houses in multiple occupation, purpose-built student accommodation and care homes. Everywhere else they are recommended for the same circuits. Where one is used, it goes at the origin of the circuit it protects.

422 — locations with a fire risk

Where there's a fire risk due to the nature of processed or stored materials, measures shall be taken to limit equipment surface temperature. The figure to know:

Chapter 42 · protection against thermal effects 421.1.201 · non-combustible consumer unit enclosure 421.1.7 · p.93 · AFDDs, socket outlet final circuits ≤ 32 A 422 · fire risk locations · 90 °C under normal conditions