A grounded circuit conductor shall be permitted to ground noncurrent-carrying metal parts of equipment on the ___ or within the enclosure of the AC service-disconnecting means.

The correct choice pertains to the grounding of noncurrent-carrying metal parts of equipment. Grounding these metal parts is essential for safety, as it helps prevent electric shock and equipment damage.

In this scenario, the phrase "supply side" refers to the side of the electrical service where electricity enters the building or facility. Grounding noncurrent-carrying metal parts on the supply side or within the enclosure of the AC service disconnecting means ensures that these parts are properly connected to the grounding system, which is crucial for maintaining safety standards.

This grounding approach helps to establish a clear fault path in the event of an electrical fault, reducing the risk of electric shock to individuals or damage to equipment. Thus, grounding on the supply side plays a vital role in the overall electrical safety strategy within installations.