1. The AFDD and RCD Mandate in Domestic/High-Risk Residential (HRR)
Amendment 2 significantly altered the requirements for detecting and isolating faults in final circuits: UK wiring regulations PDF download
Mandatory AFDDs (Regulation 421.1.7): AFDDs are now mandatory for single-phase AC final circuits supplying socket-outlets (rated up to 32 A) in specific high-risk locations. These include:
Higher Risk Residential Buildings (HRRBs - generally over 18m or six storeys).
Houses in Multiple Occupation (HMOs).
Purpose-built student accommodation.
Care homes.
Recommended AFDDs: For all other domestic premises, AFDDs for the same circuits are now recommended. This puts the onus on the installer/designer to formally justify their omission if they decide against installing them, emphasizing fire safety.
RCD Type Shift (Regulation 531.3.2): The industry standard for RCDs has effectively moved away from the basic Type AC device. Type AC RCDs are now only suitable for specific fixed equipment that cannot generate a DC component (a diminishing scenario). For all modern installations involving socket-outlets, chargers, or electronic equipment (like LED drivers), the installation of Type A RCDs (which can handle pulsating DC components) is the practical minimum requirement to prevent the RCD from being blinded.
2. Individual Circuit Protection (RCBOs)
The push toward AFDDs and the regulation aiming to limit the risk of unwanted tripping (Regulation 314.1) strongly promote the use of RCBOs (Residual Current Breaker with Overcurrent protection) over a single main RCD.
Mitigating Unwanted Tripping: By using RCBOs, a fault on one final circuit causes only that circuit to trip, preventing the loss of supply to unrelated circuits (like lighting or freezer circuits) and thereby maintaining service continuity and safety.
Space and Cost: The most common approach is now the use of AFDD/RCBO combination units, which provide arc fault, overcurrent, and residual current protection for a single circuit in a compact, two-module device. While this increases the initial cost per circuit, it greatly improves discrimination and safety.
3. New Documentation
Changes to the installation certification (EIC) reflect the need to document these devices and decisions, ensuring a clear record is left for the person ordering the work regarding the level of protection provided.
Conclusion
Overall, this variation highlights how Amendment 2 directly impacts the composition of the consumer unit. The movement away from Type AC RCDs, coupled with the mandatory or recommended use of AFDDs for socket circuits, means more devices and a greater emphasis on individual circuit protection (RCBOs). These changes are all about improving fire safety and ensuring service continuity by preventing the 'unwanted trip' of the entire installation.
