Arc Fault Detection Devices

Chapter 42

Protection against fire caused by electrical equipment

Regulation 421.1.7 has been redrafted. It is now a requirement to protect final circuits supplying socket-outlets with a rated current not exceeding 32A using AFDD’s, within certain premises (see below).

For all other premises the regulation recommends the use of AFDD’s on final circuits supplying socket-outlets with a rated current not exceeding 32A.

The new regulations are as follows:

421.1.7

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Arc fault detection devices conforming to EN62606 shall be provided for single phase AC final circuits supplying socket outlets with rated current not exceeding 32A in:

• Higher risk residential buildings
• Houses of multiple occupancy (HMO)
• Purpose built student accommodation
• Care homes

NOTE 1: Higher Risk Residential Buildings are assumed to be residential buildings over 18m in height or in excess of six storeys, whichever is met first. It is anticipated that in many areas, higher risk residential buildings will be defined in legislation which can be subject to change over time, as well as in risk management procedures adopted by fire and rescue services. Current legislation should be applied.

For all other premises, the use of AFDDs conforming to BS EN62606 is recommended for single phase AC final circuits supplying socket outlets not exceeding 32A.

Where used, AFDDs shall be placed at the origin of the circuit to be protected.

Overview

The scope of AFDD’s now changes FROM “recommended in AC final circuits”, TO, “shall be provided for single phase AC final circuits supplying sockets not exceeding 32A,” specifically in buildings where risk to life is greater, either due to the building construction or by its occupational use.

In a typical residential application, this would apply to final circuits such as the power Ring Mains, Kitchen final circuits, and also any socket final circuit in a Garage Board if one is fitted.

Amendment 2 also “recommends” the use of AFDDs on AC single phase final circuits with sockets not exceeding 32A in all other premises. Guidance on the language used within BS7671 has been included within Amendment 2, to provide definitions of key words, including the term ‘recommended’. BS7671 defines recommendation as: ‘Among several possibilities one is recommended as particularly suitable, without mentioning or excluding others”.

When installing AFDDs, they must be located at the origin of each final circuit to be protected, which is effectively within the main Consumer Unit.

The optimum solution is to use an RCBO based consumer unit, upgrading the relevant RCBOs to AFDD/RCBOs.

High integrity Dual RCCB or Split Load consumer units can be utilised, however, any cost advantage of using these solutions will be reduced as the number of circuits protected by the RCCB’s reduces.