Standard requirements for hole size in distribution boxes

Drainage or weep holes in distribution boxes for damp or wet locations must be between 3 mm (1/8 in.) and 6 mm (1/4 in.) in diameter and follow strict placement guidelines.Hole Size and QuantityDiameter: Holes must be no smaller than 3 mm (1/8 in.) and no larger than 6 mm (1/4 in.) for standard drainage openings in boxes or conduit bodies listed for damp or wet locations .Number of Holes: Typically, only a single hole is allowed per box unless the box has tightly fitted partitions, in which case one hole may be drilled in each section .Manufacturer Instructions: Larger openings may be permitted if approved by the manufacturer and installed according to their instructions .Placement GuidelinesLocation: Holes should be drilled only in the underside and at the lowest point of surface-mounted, pedestal-mounted, or pendant-mounted boxes .Prohibited Locations: Holes must not be drilled in flush-mounted boxes, hazardous (classified) locations, or where they could compromise the box's enclosure type rating .Edge Clearance: Holes should be at least 6 mm (1/4 in.) away from edges, corners, knockouts, formed conduit hubs, screw bosses, or raised areas inside the box .Raceways: Holes cannot be drilled in raceways .Installation ConsiderationsBefore Drilling: Ensure that no conductors or cables are installed in the box or raceway system prior to drilling .Approval: All drilled holes must be “approved” by the authority having jurisdiction, meaning they comply with local inspection and safety standards .Purpose: These holes are intended to prevent moisture accumulation due to condensation in damp or wet locations .SummaryTo comply with NEC and manufacturer guidelines, drainage holes in distribution boxes should be 3–6 mm in diameter, placed at the lowest point of surface-mounted boxes, and drilled only where allowed. Avoid drilling in flush-mounted boxes, hazardous locations, or near structural features that could compromise safety or enclosure ratings. Always follow manufacturer instructions and obtain approval from the local authority having jurisdiction.