What Is an RCD and Why Does Your London Home Need One?
RCDs protect against electrocution and electrical fires. Modern consumer units in London require them — here is how they work and what types exist.
The RCD (Residual Current Device) is one of the most important safety inventions in domestic electrical engineering. Yet many London homes, particularly those that have not been updated since the 1980s, still lack adequate RCD protection. Understanding what they do and why they matter can be the difference between a near-miss and a fatality.
How an RCD Works
An RCD continuously monitors the current flowing out through the live conductor and returning through the neutral conductor. In a healthy circuit these are equal. If someone touches a live wire — or if insulation breaks down and current leaks to earth — the balance changes. The RCD detects this imbalance (typically as little as 30 milliamps) and disconnects the circuit in under 40 milliseconds. That is fast enough to prevent cardiac fibrillation in most cases.
Types of RCD
Split-Load Consumer Unit
The most common arrangement in homes upgraded since the early 2000s. Circuits are split into two groups, each protected by an RCD alongside the main switch. The advantage is that a trip on one group does not affect the other. The disadvantage is that a fault on a lighting circuit, for example, will knock out all circuits on the same RCD.
High-Integrity Consumer Unit with RCBOs
An RCBO (Residual Current Breaker with Overcurrent protection) combines the functions of an MCB and an RCD in a single device. Each circuit has its own RCBO, so a fault on one circuit affects only that circuit. This is the current best-practice standard and what reputable electricians now install as default.
Portable RCD Adaptors
Socket-mounted RCD adaptors provide individual socket protection and are useful when using power tools outdoors or in wet areas where the fixed installation lacks an RCD. They are not a substitute for a properly protected consumer unit but are a legitimate additional safeguard.
RCD Socket Outlets
These incorporate RCD protection directly into the socket faceplate. They are commonly used in bathrooms for shaver sockets and in kitchens for circuits near water where a dedicated RCBO is impractical.
What the Regulations Say
BS 7671:2018 (the 18th Edition Wiring Regulations) requires RCD protection for virtually all socket outlets up to 32A in domestic premises, all circuits in bathrooms, circuits supplying equipment outdoors, and cables buried in walls at less than 50mm depth. In practice this means any compliant modern consumer unit will have comprehensive RCD or RCBO protection across all circuits.
An older consumer unit without RCDs will receive C2 (potentially dangerous) findings on any EICR, making it effectively non-compliant.
Testing Your RCDs
Every RCD has a test button. The IET recommends pressing it quarterly to confirm the device operates. The circuit should trip immediately. If it does not, the RCD has failed and must be replaced — a failed RCD provides no protection whatsoever. Reset by pushing the switch back to the on position after testing.
Why London Properties Lag Behind
London has a disproportionate number of older properties — particularly Victorian and Edwardian conversions — where the electrical installation has been partially updated over decades rather than rewired in full. It is common to find a modern consumer unit with RCDs installed as recently as 2010 feeding circuits that are still running on original 1960s wiring. The RCD will offer protection, but the degraded wiring behind it remains a risk. A full EICR is the only way to assess the complete picture.