Where you're installing GFCI receptacles or need more room for connectors and devices, use a 4S deep box. Finally, cover 4-square boxes with a mud-ring cover. This. Electrical enclosure sizes are not universal, but most manufacturers follow common size families. This guide explains typical wall-mount and floor-standing dimensions, how to read catalog sizes, and how to choose the right enclosure size for your layout. A distribution box, sometimes referred to as a panel board, distribution board, or breaker panel, is an.