An RCD, or Residual Current Device, is a safety device used in electrical installations to prevent electric shock and reduce the risk of electrical fires. It works by monitoring the flow of electricity through a circuit and quickly disconnecting the power if it detects an imbalance, which may indicate a fault or leakage of current. RCDs are commonly used in homes and commercial buildings, often installed in circuit breakers or as standalone units. They are essential for protecting people and property, especially in areas where electrical equipment is used near water, such as bathrooms and kitchens.