Cable tray with reserved cable holes

Reserved or pre-punched holes in cable trays are used for drainage, cable entry/exit, and accessory attachment, with specific spacing and placement requirements depending on tray type and installation environment.

Purpose of Reserved Holes

Reserved holes in cable trays serve several key functions: Drainage: Solid-bottom trays can collect moisture; reserved holes allow water to drain, preventing corrosion and cable damage (recommended 1/4-inch weep holes every 3 feet along the tray bottom).

Cable Entry/

Exit: Holes facilitate routing of small-diameter instrumentation or control cables through the tray without cutting or damaging the tray structure. Accessory Attachment: Pre-punched holes on side rails or rungs allow easy installation of brackets, covers, or other accessories without additional drilling. Hole Placement and SpacingSolid-Bottom Trays: Holes should be located at the sides and middle of the tray bottom to ensure effective drainage, especially in outdoor or humid environments.

Ventilated or Ladder Trays: Ventilation holes or rungs may double as cable exit points; spacing is typically designed to support cable weight and maintain bend radius (rung spacing 6–9 inches for small instrumentation cables). Accessory Holes: Side rails often come with pre-punched holes for mounting accessories; these should align with manufacturer specifications to maintain structural integrity. Standards and ComplianceNEC 392: Cable trays must remain accessible, and metallic trays can serve as grounding conductors if compliant.

Reserved holes should not compromise tray strength or violate fill limits (40% for power cables, 50% for control cables). Material Considerations: Aluminum, steel, or FRP trays may have different hole size tolerances due to mechanical properties and corrosion resistance.

Practical Recommendations

Verify that reserved holes do not reduce tray load capacity or create sharp edges that could damage cables. Use manufacturer guidelines for hole size, typically 1/4 inch for drainage and larger for cable entry or accessory mounting. Ensure proper alignment of holes for modular tray systems to facilitate future expansion or maintenance.

By following these guidelines, reserved holes in cable trays can provide effective drainage, safe cable routing, and convenient accessory installation while maintaining compliance with NEC and manufacturer standards.