Can holes be drilled at the bottom of cable trays

Yes, holes can be drilled at the bottom of a cable tray, but the purpose, location, and protective measures must be carefully considered.

Solid-

Bottom Cable Trays

For solid-bottom cable trays, drilling holes is commonly done to prevent water accumulation or to allow cables to exit the tray. When installed outdoors or in humid environments, it is recommended to drill ¼-inch weep holes at the sides and middle every 3 feet to limit moisture retention, unless EMI/RFI shielding is required, as holes would compromise shielding effectiveness (Eaton B-Line series guidance).

Cable Exit and Field Modifications

Holes may also be drilled to allow cables to exit the tray. In such cases, abrasion protection is important. Snap-in bushings or cable channel bushings should be used to protect cable jackets from sharp edges (Eaton B-Line series).

Field drilling for splice plates or dropouts is also standard practice, with care taken to remove burrs and apply rust-proofing or protective coatings to maintain tray integrity.

Guidelines and Safety Considerations

Hole size and spacing: Typically, ¼-inch holes for drainage or 5/16 to 7/16-inch for cable exit, depending on hardware and cable size. Avoid compromising structural integrity: Drill only where necessary and avoid weakening side rails or load-bearing sections. EMI/RFI shielding: Do not drill holes in trays that require electromagnetic shielding, as this will reduce effectiveness.

Compliance: Ensure that modifications comply with NEC Article 392, which governs cable tray installation and cable types.

Summary

Drilling holes at the bottom of a cable tray is permissible and often necessary for drainage or cable routing, especially in solid-bottom trays. Proper hole size, spacing, protective bushings, and adherence to code requirements are essential to maintain safety, structural integrity, and cable protection.