Requirements for cable trays in building low-voltage electrical shafts

Cable trays for low-voltage electrical shafts must be properly supported, grounded, fire-stopped, and installed according to IEC standards and manufacturer specifications to ensure safety, durability, and accessibility.

Structural Support and Load Capacity

Cable trays must be independently supported from the building structure. Each support, including fastenings, should be capable of carrying the present and future load multiplied by a safety factor of at least four or 200 lbs., whichever is greater. Expansion connectors are required where trays cross building expansion joints or in runs exceeding 90 feet to accommodate thermal expansion and structural movement.

Fire and Smoke Barrier Penetrations

When cable trays penetrate fire or smoke barriers such as walls, floors, or ceilings, firestopping must be installed after cables are placed. This ensures compliance with fire safety codes and prevents the spread of smoke or flames through the shaft.

Grounding and Electrical Continuity

Cable trays must be grounded and bonded to maintain continuous electrical conductivity. The tray itself can serve as an equipment ground conductor, but it should not be used as a ground for connected equipment unless specified. Proper grounding reduces the risk of electrical hazards.

Tray Types and Material SelectionLow-voltage applications often use ventilated, solid-bottom, or wire-mesh trays depending on cable type, heat generation, and electromagnetic interference considerations. Materials such as steel, stainless steel, or aluminum are selected based on mechanical strength, corrosion resistance, and environmental conditions. Wire-mesh trays are preferred for instrumentation and control cables due to flexibility and protection against interference.

Installation and Maintenance Considerations

Minimum bend radius must be maintained to prevent cable damage. Rung spacing of 6–9 inches is recommended for small instrumentation cables. Accessibility must be ensured for valves, junction boxes, hatches, and other operational components after installation.

Cable trays should not be used as walkways or ladders. Compliance with StandardsInstallation should follow IEC 61537 for metallic cable tray systems, which covers mechanical strength, corrosion resistance, fire performance, ventilation, fill ratio, and compatibility with fittings. Compliance ensures safety, durability, and interoperability across installations.

National standards and CE marking may also apply depending on location. By adhering to these requirements, low-voltage cable trays in electrical shafts will provide safe, reliable, and maintainable cable management for telecom, security, and A/V systems.