How does a Residual Current Device (RCD) protect against electric shocks?

A Residual Current Device (RCD) protects against electric shocks by rapidly disconnecting the electricity supply when a fault is detected.

An RCD is a life-saving device that is designed to prevent you from getting a fatal electric shock if you touch something live, such as a bare wire. It provides a level of protection that ordinary fuses and circuit breakers cannot offer.

The RCD monitors the electric current flowing through one or more circuits it is protecting. It works by constantly comparing the current flowing into an electrical device with the current flowing out. In a healthy circuit, these two currents are equal. However, if there is a fault (for example, if a person touches a live part and provides a path to earth), the electrical current will take a different path and the balance of the current will be disturbed.

When the RCD detects this imbalance, it switches off the electricity supply to the circuit within a fraction of a second, fast enough to turn off the electricity before it can cause harm. The speed of the reaction is crucial, as the faster the electricity is cut off, the less severe the electric shock.

RCDs are designed to disconnect the circuit if the leakage current (the difference between the current going in and coming out) exceeds a certain level, typically around 30 milliamperes. This level of current is enough to cause cardiac arrest if it passes through the chest area, so the RCD acts to prevent this from happening.

In summary, an RCD is a vital safety device that protects against electric shocks by constantly monitoring the electric current and rapidly disconnecting the supply if a fault is detected. It is a crucial component in any electrical installation and can save lives.