Under what conditions can lightning and telephone grounding be grounded to the same water pipe?

The correct answer is grounded to the same water pipe when the water pipe is electrically continuous. This is important because for grounding to be effective, it must provide a low-resistance path to dissipate electrical surges safely into the earth. An electrically continuous water pipe ensures that there is a reliable connection that can effectively conduct any lightning or electrical surge safely away from the building and its occupants.

Ensuring that both lightning and telephone grounding systems share the same grounding electrode—such as an electrically continuous water pipe—can also help to maintain consistent reference points for the electrical systems. This minimizes the risk of voltage differences that could lead to dangerous surges or electrical shock events.

Proper grounding practices, including the use of continuous water pipes, help in maintaining safety standards and protecting the electrical systems and devices within a structure from lightning strikes and other electrical anomalies.