When investigating high-neutral voltage or lightning vulnerability, what is the first step that should be taken?

The first step when investigating high-neutral voltage or lightning vulnerability is to measure the ground resistance with a clamp-on tester. This is crucial because understanding the ground resistance gives insights into the effectiveness of the grounding system, which is vital in preventing equipment damage during voltage spikes such as those from lightning strikes. A low ground resistance indicates that the grounding system is functioning properly and can safely dissipate excess voltage into the earth.

This initial measurement establishes a baseline for the grounding system's capability to handle transient events. If ground resistance is high, it could lead to ineffective grounding, increasing the risk of equipment damage or failures during electrical disturbances.

The other choices, while they may contribute to a comprehensive assessment, do not serve as the critical first step in the investigation. For example, measuring voltage levels with a multimeter evaluates the current electrical situation but does not assess the grounding system's performance. Inspecting switchgear for damage or checking for physical obstructions can follow once the grounding system's effectiveness is determined, but they rely on having established a proper grounding resistance first.