What is the main function of the main earthing conductor in a MEN installation?

The main function of the main earthing conductor in a Multiple Earthed Neutral (MEN) installation is indeed to connect parts that need earthing to the mass of earth. This is crucial for electrical safety, as it helps to ensure that any fault or leakage current can safely dissipate into the ground, reducing the risk of electric shock or fire. Proper grounding facilitates the protection of electrical systems and personnel by providing a path for fault currents to flow, thereby enabling protective devices like circuit breakers to operate effectively and disconnect the supply in the event of a fault.

In this context, the other options do not accurately describe the purpose of the main earthing conductor. While ensuring safe operation under high voltage, providing power to auxiliary circuits, and regulating temperature may all involve electrical systems in some capacity, they do not pertain directly to the function of earthing. The main earthing conductor's primary role is focused on electrical safety through proper grounding and earthing practices, making option A the correct choice.