What size of sphere cannot pass through openings in doors to be exempt from hazardous location regulations?

The correct answer is 3 inch. According to hazardous location regulations, particularly related to the protection of electrical equipment and ensuring safety in potentially hazardous environments, equipment must be designed to prevent the entry of foreign materials, including spheres of a specified size.

In this context, a sphere with a diameter greater than 3 inches is considered too large to pass through openings typically found in doorways, thereby becoming subject to additional hazardous location regulations. This is intentional; allowing only smaller spheres to pass through openings minimizes risk, ensuring that larger objects—which could represent potential hazards—are restricted from entering spaces that require stringent safety measures.

By contrast, spheres measuring 2 inches or smaller are usually exempt from such regulations because they can easily pass through these openings without posing an increased risk. The 4 inch and 5-inch spheres exceed the threshold, thus necessitating compliance with the regulations to ensure safety in those environments. The 3-inch sphere serves as the pivotal size, marking the transition point where items become regulated under hazardous location guidelines.