The grounding electrode conductor for an antenna mast must be _____ when subject to physical damage.

The correct choice is that the grounding electrode conductor for an antenna mast must be protected when it is subject to physical damage. This requirement is essential to ensure both the safety and functionality of the grounding system.

Grounding electrode conductors play a crucial role in providing a safe path for electrical faults, including lightning strikes, thereby protecting the antenna system and any associated electrical equipment. When these conductors are exposed to physical hazards—such as traffic, weather, or equipment movement—they can be damaged, compromising their effectiveness and potentially leading to safety issues.

By requiring that these conductors be protected, building and electrical codes help ensure that the grounding system remains intact and fully functional. This protection can take the form of physical barriers, conduits, or other methods that shield the conductor from external risks.

Other options, while applicable in certain contexts, do not specifically address the need to mitigate physical damage directly. Therefore, protection is the most relevant requirement in this scenario.