Cable trays laid on the ground

Cable trays can be installed along the ground, but proper grounding, bonding, and adherence to NEC standards are essential for safety and reliability.

Installation Considerations

Cable trays laid along the ground are commonly used in industrial and commercial facilities where overhead installation is impractical. They must remain accessible for maintenance and should not be placed in areas prone to severe physical damage or flooding. Only conductors rated for open-air environments, such as Tray Rated (Type TC) or Metal-Clad (Type MC) cables, should be used in these trays, and fill limits must be observed—typically 40% for power cables and 50% for control cables to prevent overheating.

Grounding and Bonding

Grounding is critical for cable trays on the ground. Metallic trays can serve as the Equipment Grounding Conductor (EGC) if they meet NEC requirements, or a separate grounding conductor can be installed along the tray. Each tray section should be bonded to the next using clamps, bolts, or splice plates to ensure electrical continuity.

For installations with multiple cables, the EGC in the cables should also be bonded to the tray sections to prevent displacement under fault conditions. Material considerations: Avoid placing bare copper conductors in aluminum trays in moist environments to prevent electrolytic corrosion; insulated conductors with exposed bonding points are preferred. Grounding resistance: The grounding system should ideally have a resistance of 4 ohms or less to ensure effective fault current dissipation.

Bonding jumpers: These should be sized according to the minimum requirements for equipment grounding conductors and connect all tray sections, conduit, or cable drops back to the power source.

Safety and Compliance

Cable trays on the ground must comply with NEC Article 392, which prohibits installation in hoistways or enclosed spaces and requires proper separation of high-power and low-power cables to minimize electromagnetic interference (EMI),. Grounding protects personnel from electric shock, prevents equipment damage, and reduces fire hazards caused by fault currents or lightning strikes.

Environmental and Mechanical Considerations

Corrosion resistance: Use galvanized steel, stainless steel, or copper for grounding wires depending on environmental conditions. Mechanical protection: Ground-level trays should be protected from physical damage, moisture, and corrosive substances. Consider using covers or elevated supports if necessary.

Thermal expansion: If trays are exposed to sunlight or temperature variations, expansion splice plates may be required to accommodate movement. By following these guidelines, cable trays laid along the ground can provide a safe, reliable, and code-compliant solution for routing electrical conductors in industrial and commercial installations.