Which of these precautions should be taken when installing devices for lightning protection in a coaxial cable feedline?

When installing devices for lightning protection in a coaxial cable feedline, grounding all of the protectors to a common plate connected to an external ground is crucial for effective protection. This method ensures that any surge caused by a lightning strike can be safely dissipated into the ground, minimizing the risk of damage to the equipment and providing a path for the electrical surge to follow away from sensitive components.

A common grounding point helps ensure that there is no significant voltage difference between different grounds that could arise if they were all connected separately. This is important because if there are multiple ground points connected separately, a potential difference could lead to a lightning strike traveling through the system, causing damage rather than being properly grounded.

The other options, while they may have their own purposes in certain contexts, do not address the primary need for a cohesive, common ground system that effectively mitigates lightning-related surges. Therefore, grounding all protectors to a common plate allows for the safest and most reliable operation of the lightning protection system.