What are the requirements for AFDDs in BS 7671:2018+A2:2022?
The requirements for AFDDs in BS 7671:2018+A2:2022 are focused to provide protection in buildings where a fire could lead to major consequences. AFDDs offer most benefit for arc faults which may occur in equipment plugged into the electrical installation, hence the requirement concentrates on circuits supplying socket-outlets.
Regulation 421.1.7 of BS 7671:2018+A2:2022 requires AFDDs to be provided for single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32 A in:
• Higher Risk Residential Buildings (HRRB)
• Houses in Multiple Occupation (HMO)
• Purpose-built student accommodation
• Care homes.
For all other premises, the use of AFDDs is recommended for single-phase AC final circuits supplying socket-outlets not exceeding 32 A. However, this is a recommendation and not a requirement, which means it is a consideration for the designer and not something that shall be done.
What is a higher-risk building?
A higher-risk building is now defined in Legislation.
The Building Safety Act 2002 considers a higher-risk building to be at least 18 metres in height or has at least 7 storeys and contains at least 2 residential units. However, it is recognised that height and use are not the only indicators of risk.
At the time of producing BS 7671:2018+A2:2022, The Building Safety Bill was still working its way through Parliament and the term used at the time was Higher Risk Residential Buildings (HRRB). It has since become Legislation, namely The Building Safety Act 2002, which came into force on 28th April 2022. The term HRRB has been amended to ‘higher-risk buildings’, this will need to be updated in the next Amendment to BS 7671.
When do I need to install AFDDs?
AFDDs are required when carrying out new electrical installation work in the types of buildings mentioned previously, whether it is a complete installation or an addition or alteration to an existing circuit.
It is not a requirement to upgrade an existing circuit to include AFDDs when carrying out simple maintenance work such as like-for-like replacements. The requirements of BS 7671 are not retrospective, so, existing installations do not require upgrading.