Can control cable trays be buried underground

Tray cables can only be buried underground if they are specifically rated for direct burial; otherwise, they must be installed in a protective conduit or raceway.Direct Burial Requirements

Not all tray cables are suitable for underground installation. Only cables explicitly marked as “Direct Burial” (DB) are designed to withstand soil conditions, moisture, chemical exposure, and physical stresses such as crushing or impact from rocks and earth pressure without additional protection . These cables typically use specialized insulation and jacketing materials like abrasion-resistant PVC, polyethylene, or cross-linked polyethylene (XLPE) to ensure durability underground .

Protective Measures for Non-Direct Burial Cables

If a tray cable is not rated for direct burial, it cannot be placed directly in the ground. In such cases, the cable must be installed inside an approved raceway or conduit, such as rigid metal conduit (RMC) or Schedule 40/80 PVC, to protect it from mechanical damage, soil chemicals, and shifting earth . The type of conduit used also affects the required burial depth; for example, non-metallic PVC conduit typically requires a minimum cover of 18 inches, while rigid metal conduit may allow shallower burial, such as 6 inches .

Regulatory and Safety Considerations

Compliance with standards is essential. In the U.S., the National Electrical Code (NEC) governs underground cable installations, specifying minimum burial depths, protective measures, and cable types suitable for direct burial . In the U.K., BS 7671 provides guidance on buried cable installation, including reference methods for protection, backfilling, and mechanical stress mitigation . Proper backfill, such as sand or fine aggregate, is recommended to cushion the cable and prevent damage from sharp objects or heavy loads .

Summary

• Direct burial tray cables: Can be installed directly in the ground without additional conduit if marked for DB use .
• Non-direct burial tray cables: Must be installed in a protective conduit or raceway to comply with safety standards and prevent premature failure .
• Protective measures: Include proper conduit selection, minimum burial depth, and suitable backfill to prevent mechanical damage and moisture ingress . Always verify the cable's manufacturer ratings and local electrical codes before burying any tray cable underground to ensure safety and compliance.