How to pull the cable tray at bends

Proper cable pulling at tray bends requires controlling tension, maintaining minimum bend radii, and using sheaves or rollers to prevent damage and ensure long-term reliability.

Key Considerations

Bend Radius: Cables must be pulled around bends without exceeding their minimum bend radius, which is typically specified by the manufacturer. Exceeding this radius can deform conductors, damage insulation, and reduce electrical performance ( ). Pulling Tension: The maximum pulling tension depends on cable construction and weight. While bends in cable trays do not multiply tension like conduit bends if sheaves are used, the force required to bend the cable around the sheave must still be considered ( ). For heavier cables, tension calculations should include sidewall bearing pressure (SWBP), which is the force exerted on the cable by the bend ( ). Sheaves and Rollers: Using well-maintained sheaves or rollers at bends reduces friction and prevents tension multiplication. If sheaves are poorly maintained, the bend can increase pulling force, potentially damaging the cable ( ). Lubricants compatible with the cable jacket can further reduce friction during the pull. Sidewall Bearing Pressure (SWBP): SWBP is critical when pulling multiconductor cables through bends. It is influenced by the bend radius, cable weight, and pulling tension. Larger bend radii reduce SWBP, minimizing the risk of crushing or insulation damage ( ). Planning and Pathway Design: Effective cable pulling requires planning around pathway geometry, friction points, and support spacing. Properly supported cable trays and adherence to NEC or local codes ensure safe installation and long-term reliability ( ).

Best Practices

• Always follow manufacturer specifications for maximum pulling tension and minimum bend radius.
• Use rollers or sheaves at bends to reduce friction and prevent tension multiplication.
• Apply compatible lubricants if necessary, especially for long or heavy cable runs.
• Calculate SWBP for multiconductor cables to ensure the bend does not exceed safe limits.
• Plan the pull route carefully, considering horizontal and vertical bends, cable weight, and tray support spacing.
• Avoid using cable trays as walkways or supports for personnel, as this can damage cables and compromise safety ( ). By following these guidelines, cable installers can ensure that cables are pulled safely through tray bends, maintaining both mechanical integrity and electrical performance.