Understanding RCD Types (BS 7671 Regulation 531.3.3)

Residual Current Devices (RCDs) are critical for life safety, but modern electronic loads have made selection highly complex. Standard Type AC RCDs can be 'blinded' by pulsating DC current leaking from modern appliances, rendering them useless in the event of a fatal shock.

Modern RCD Classifications

• Type A: The baseline standard for modern UK homes. Detects standard AC faults and pulsating DC components generated by LED lighting, switch-mode power supplies, and general household electronics.
• Type F: Required for single-phase frequency-controlled motors, such as modern washing machines, air conditioning units, and domestic air-source heat pumps.
• Type B: Mandatory for three-phase systems, Electric Vehicle (EV) chargers lacking internal DC protection, and large-scale Solar PV arrays. Type B detects smooth DC residual currents.