Residual Current Device
The RCD working principle is based on this one fact the same current flowing in the live wire will always return through the neutral wire, as long as there is no leakage to earth. If there is a leakage the current will take an alternative route to earth through our body
A residual current device (RCD) is a safety device that switches off electricity automatically if there is a fault. RCDs are far more sensitive than normal fuses and circuit-breakers and provide additional protection against electric shock.
Additional protection by means of an RCD can be a lifesaver. An RCD constantly monitors the electric current flowing along a circuit. If it detects electricity flowing down an unintended path, such as through a person who has touched a live part, it will switch the circuit off very quickly, thereby significantly reducing the risk of death or serious injury.
Using electricity whilst wet significantly increases the risk of electric shock. If you are wet and in contact with the ground, it makes it easier for the electricity to flow through you. RCDs can help protect you from electric shock in areas, such as in bathrooms and gardens, where you may be wet.