What does the primary conductor in a counterpoise system connect?

In a counterpoise system, the primary conductor serves a critical function in providing an effective pathway for lightning energy to be safely directed and dissipated into the ground. The correct answer reflects this role accurately, as the primary conductor connects all down conductors at or below grade.

This is essential for ensuring that lightning strikes can be effectively channeled through the grounding system. By linking all down conductors, it establishes a unified system that facilitates the safe transfer of electrical energy from air terminals – which are the points where the lightning strikes – to the grounding system, allowing it to disperse safely into the earth.

The other choices, while related to different aspects of lightning protection systems, do not correctly describe the primary function of the primary conductor in a counterpoise configuration. They mention connections to air terminals, fasteners, or bonding points but do not specifically address the role of connecting down conductors, which is fundamental for ensuring the efficacy of the lightning protection system.