RCD Selection Guide — BS 7671 18th Edition

This guide recommends the appropriate RCD (Residual Current Device) type and trip rating based on BS 7671 18th Edition wiring regulations. RCDs are life-saving devices that detect earth fault currents and disconnect the supply to prevent electric shock and fire.

RCD types explained

• Type AC: Detects sinusoidal AC fault currents only. Since Amendment 2 (27 Sep 2022) it may only be used for fixed equipment whose load contains no DC component — e.g. simple filament lamps or resistive heaters with no electronic driver. Not suitable for general domestic circuits or LED lighting.
• Type A: Detects AC and pulsating DC fault currents. Required for circuits with electronic equipment (computers, chargers, LEDs with drivers). Now the standard for most domestic circuits.
• Type B: Detects AC, pulsating DC, and smooth DC fault currents. Required for some EV chargers, PV inverters, and variable speed drives.
• Type F: For circuits feeding equipment with frequency inverters (VFDs). Rarely needed in domestic installations.

Trip ratings

• 30mA: Personal protection against electric shock. Required for most domestic circuits per BS 7671.
• 100mA: Fire protection. Used where personal protection is not the primary concern.
• 300mA: Fire protection for larger installations. Common in commercial switchgear as upstream protection.

Key BS 7671 regulations

Regulation 411.3.3 requires 30mA RCD protection for socket outlets up to 32A. Regulation 411.3.4 (added by Amendment 4, BS 7671:2018+A4:2026) requires 30mA RCD protection for AC final circuits supplying luminaires in domestic premises. Regulation 522.6.202 requires 30mA RCD protection for cables concealed in walls at a depth of less than 50mm. Regulation 701.411.3.3 requires a 30mA RCD for all circuits in a location containing a bath or shower. For EV charge points, Regulation 722.531.3.101 requires at least a Type A RCD plus protection against DC fault currents above 6mA. The guide cross-references these regulations based on your circuit type and application.