Standard explained
RCD Protection Explained
An RCD (residual current device) rapidly disconnects the supply when it detects earth leakage, providing vital additional protection against electric shock and fire.
A residual current device (RCD) is a protective device that constantly compares the current flowing out on the line conductor with the current returning on the neutral. If it detects an imbalance — meaning current is leaking to earth, potentially through a person — it disconnects the supply within milliseconds.
Why RCDs matter
RCDs provide additional protection against electric shock, particularly where other measures might fail or where cables could be damaged. A 30 mA RCD is the common rating for personal protection.
Where RCD protection is required
BS 7671 requires RCD protection for a broad range of circuits, including:
- socket-outlets for general use;
- cables concealed in walls at a depth where they could be damaged; and
- circuits in locations with increased risk.
On an EICR
Missing RCD protection where it is now required is one of the most common observations. Depending on the circuit and risk, it is typically coded C2 or C3. Upgrading often means fitting RCBOs or an RCD-protected consumer unit — see RCBO protection and distribution boards.
Frequently asked questions
Do all circuits now need RCD protection?
BS 7671 requires RCD protection for a wide range of circuits — including socket outlets and cables concealed in walls — with limited exceptions. Older installations without it are commonly coded C2 or C3 on an EICR depending on the circumstances.
Related service
RCD, RCBO & SPD Upgrades
Improved protection through residual-current, overcurrent and surge protective devices.
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BS 7671 — the IET Wiring Regulations — is the national standard for the safety of electrical installations in the UK, currently the 18th Edition.
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Cable selection under BS 7671 balances current-carrying capacity, installation method, grouping, ambient temperature and voltage drop so conductors run safely.
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Distribution Boards and Consumer Units Explained
Distribution boards (and domestic consumer units) house the protective devices that control and protect each circuit — their condition is central to any EICR.
Learn moreThis article provides general guidance and distinguishes legislation, British Standards and good practice. It is not legal advice. Always confirm the specific duties applying to your property and tenure.