Why is a protective earthing conductor necessary in a final subcircuit with an RCD?

A protective earthing conductor is essential in a final subcircuit containing a Residual Current Device (RCD) because it enables the proper operation of the RCD. The RCD is designed to detect and respond to imbalances between the live and neutral conductors, which indicates a leakage current possibly caused by a fault, such as a person coming into contact with a live wire. The protective earthing conductor provides a safe path for fault current to flow to the ground.

This direct earthing path ensures that if there is a fault condition, it can help facilitate a quick disconnection of the supply, thereby reducing the risk of electric shock. The proper functioning of the RCD relies on the effectiveness and integrity of the earthing system because it needs an accurate reference point to monitor leakage currents. In the absence of earthing, the RCD may not function correctly, leading to potential safety hazards.

In contrast, other factors mentioned, such as reducing electrical noise, enhancing the power factor, or preventing circuit overload, do not directly relate to the primary role of a protective earthing conductor in enhancing the safety and operational efficiency of an RCD-equipped circuit.