Information
Definition
A Residual Current Device (RCD) is a protective device that disconnects a circuit when it detects an imbalance between live conductors that may indicate earth leakage current. In EV charging, RCD selection must consider AC residual current, possible DC residual current and the protection already built into the charger.
Why it matters
It matters because incorrect RCD selection can compromise safety or cause nuisance tripping, especially where EV charging equipment can produce DC residual current. UK installers and specifiers need to understand how RCD type, RDC-DD protection and BS 7671 requirements interact.
References
Standards and regulations
BS 7671
BS 7671 is the UK national standard for electrical installations, covering the design, erection, inspection, testing and verification of low-voltage electrical systems. Section 722 contains specific requirements for supplies to electric vehicles.
EN 62955
EN 62955 is the UK-relevant BS EN IEC standard for Residual Direct Current Detecting Devices used in Mode 3 EV charging equipment. It is commonly associated with 6 mA DC residual current detection and how EV chargers interact with upstream RCD protection.