What Is an RCD?
An RCD (Residual Current Device) is a safety device that monitors the current flowing through a circuit and instantly cuts the power if it detects current leaking to earth — for example, through a person receiving an electric shock. It's a different kind of protection to a fuse or circuit breaker, which guards against overload and short circuits rather than personal injury.
How does an RCD work?
An RCD constantly compares the current flowing through the live and neutral wires. Under normal conditions, these should be equal — whatever current flows out through live should flow back through neutral. If some of that current escapes to earth instead, perhaps because someone has touched a live part, the RCD detects the imbalance and disconnects the circuit within milliseconds, well before a dangerous shock can occur.
What's the difference between an RCD and a fuse or MCB?
A fuse or miniature circuit breaker (MCB) protects the wiring and connected equipment from overload or short-circuit faults — too much current flowing through the circuit. An RCD is specifically designed to protect people from electric shock, and operates independently of how much current is actually flowing, focusing instead on whether it's flowing where it should be.
What is an RCBO?
An RCBO combines the functions of an RCD and an MCB into a single device, providing both types of protection for one specific circuit. This is generally considered a more precise form of protection than a single RCD covering multiple circuits, since a single fault only trips the RCBO for that one circuit rather than affecting others sharing the same RCD.
Do all UK homes have RCD protection?
Current UK wiring regulations require RCD protection for most socket circuits and specific other circuits in domestic properties. Older installations may not have this protection throughout, particularly if the consumer unit hasn't been updated in some time. If you're unsure whether your home has adequate RCD protection, a qualified electrician can check your consumer unit and advise.
Frequently Asked Questions
What is an RCD?
An RCD is a safety device that detects current leaking to earth and disconnects the circuit within milliseconds, protecting against electric shock.
What's the difference between an RCD and a circuit breaker?
A circuit breaker (MCB) protects against overload and short circuits. An RCD protects against electric shock by detecting current leaking to earth. They serve different purposes and are often used together.
What is an RCBO?
An RCBO combines RCD and MCB protection into a single device for one circuit, offering more precise protection than a single RCD shared across multiple circuits.
Does my home need RCD protection?
Current UK regulations require RCD protection for most socket circuits in domestic properties. If your consumer unit hasn't been updated recently, it's worth having a qualified electrician check your level of protection.