Which of the following does not require an equipment grounding conductor?

The correct answer is a double insulated hand tool because such tools are specifically designed with an insulation system that provides a high level of protection against electrical shock. These tools eliminate the need for a separate equipment grounding conductor as the design reduces the risk of exposure to live parts.

Double insulation means that there are two layers of insulation between the electrical components and the exterior of the tool, creating a fail-safe mechanism; if one insulation layer were to fail, the second layer would still protect the user. Therefore, these types of hand tools do not require an equipment grounding conductor to ensure user safety.

On the other hand, metallic hand tools, electrical appliances with exposed parts, and three-pronged plug devices inherently rely on a grounding system for safety. Metallic hand tools can conduct electricity if there is a fault, and thus need grounding to protect the user from electric shock. Similarly, electrical appliances with exposed parts are at risk of becoming energized, and a grounding conductor provides a path for fault current to prevent electric shock. Three-pronged plugs are designed to connect to a grounded outlet, ensuring additional safety measures are in place during operation.