Where metallic plugs or plates are used with non-metallic enclosures, they shall be recessed ______.

The requirement for metallic plugs or plates used with non-metallic enclosures to be recessed is established to ensure safe and effective installation, minimizing any potential hazards. When metallic components are employed, they can create points of electrical contact that, if not properly recessed, could lead to potential shock hazards, grounding issues, or even arcing.

The specific measurement of 1/4" is mandated in the regulations to maintain a safe distance between the surface of the non-metallic enclosure and the metallic parts. This distance helps prevent accidental contact with the metallic surfaces while also providing enough space to avoid any mechanical interference or damage during installation.

Using a smaller recess measurement, such as 1/4", balances safety with practicality, ensuring that the components fit correctly and function as intended without unnecessary complications or risks.