What protective device must be installed on all underground, exposed power conductors that lead underground?

The installation of properly grounded lightning arrestors on all underground, exposed power conductors that lead underground is essential for safeguarding the electrical infrastructure, especially in mining operations where exposure to electrical hazards is a significant concern. Lightning arrestors serve to divert excess voltage from lightning strikes or surges away from the power conductors, mitigating the risk of equipment damage and ensuring the safety of mine personnel.

In the context of underground mining, where conditions can be unpredictable and equipment is often subject to moisture and other environmental factors, having grounded lightning arrestors provides a critical layer of protection against electrical failures and hazards. This is particularly relevant in mountainous terrains, such as that found in West Virginia, where sudden weather changes can lead to electrical surges.

Other options, while they play roles in electrical safety and management, do not specifically address the immediate need to protect power conductors from lightning or similar surge instances. The focus on grounding in the correct choice emphasizes both the necessity for operational safety and the prevention of costly electrical issues in an underground setting.