When is it necessary for screw threads to make contact with bare metal?

The necessity for screw threads to make contact with bare metal is critical when a ground screw is required. This ensures proper grounding of the electrical system, which is essential for safety and functionality. Grounding provides a path for electrical current to safely dissipate into the earth in the event of a fault or surge, minimizing the risk of shock, fire, or damage to equipment.

In the context of using a ground screw, the bare metal contact allows for reliable electrical conductivity. If the screw threaded connection does not touch bare metal, it could create resistance in the grounding path, potentially leading to inadequate grounding and safety hazards.

The other scenarios mentioned, such as installing fuses, connecting wires to a circuit, or using insulated tools, do not necessitate bare metal contact through screw threads for proper function or safety in the same way. These situations may involve different requirements, such as using proper terminals or maintaining insulation, which do not rely on the same principle of grounding.