How to construct underground cable trays

Underground cable trays are installed by carefully planning the route, preparing a trench with protective bedding, laying the trays and cables, and covering them with protective layers to ensure safety and durability.

Planning and Route Preparation

Before any excavation, plan the cable tray route according to your site layout, electrical design, and load requirements. Consider clearance, future maintenance access, and separation from other utilities. Mark the route clearly to avoid obstacles and ensure proper alignment of the trays .

Trench Excavation and Bedding

• Excavate a trench typically 1.5 meters deep and 0.45–0.5 meters wide, depending on cable size and number of trays .
• Lay a 10 cm layer of fine sand at the bottom of the trench to act as a cushion and prevent moisture from damaging the cables .
• For multiple cables, maintain horizontal or vertical spacing of at least 30 cm to reduce mutual heating and prevent damage in case of faults .

Installing Cable Trays

• Place cable trays or troughs (made of cement, stoneware, or metal) along the trench .
• Ensure trays are aligned, level, and securely supported. Use appropriate clamps and brackets if trays are suspended or mounted on supports .
• For long runs, consider using cable tray rollers to facilitate smooth cable laying and prevent kinks .

Laying Cables

• Lay the cables carefully on the sand bed inside the trays, ensuring no sharp bends or tension.
• Cover the cables with another 10 cm layer of sand to protect against mechanical damage .
• For additional protection, place bricks or protective covers over the sand layer before backfilling with soil .
• Cables should have bituminized paper and hessian tape to prevent corrosion and electrolysis .

Protective Measures and Compliance

• Apply a warning tape above the cable layer to alert future excavators .
• Ensure compliance with National Electrical Code (NEC) or local standards for minimum cover depth and conduit protection .
• For high-risk areas, consider PVC or metal conduits to provide extra mechanical protection and facilitate future cable replacement .

Final Steps

• Backfill the trench carefully, compacting soil without damaging the trays or cables.
• Test the cables for continuity, insulation resistance, and proper grounding before energizing the system .
• Maintain clear documentation of the cable route for future maintenance or upgrades. By following these steps, underground cable trays can be installed safely, efficiently, and in a way that ensures long-term reliability and compliance with electrical standards .