How deep must the threads be engaged when using the drilling and tapping method for an air terminal?

The correct answer is that the threads must be engaged at least five-eighths of an inch when using the drilling and tapping method for air terminals. This depth ensures that there is sufficient mechanical engagement between the air terminal and the grounding system, providing a reliable and stable electrical connection. The depth is critical in maintaining the integrity of the lightning protection system, as it affects the conductivity and physical stability of the connection. A deeper engagement helps to resist loosening due to environmental factors and ensures that the air terminal can effectively channel lightning strikes to the ground without failure.

It's important to follow established standards and practices in lightning protection, as insufficient engagement can lead to increased resistance, which may compromise the system's effectiveness during a lightning event. This consideration is crucial for ensuring safety and performance for any structure equipped with a lightning protection system.