The cable tray removal coefficient is effectively the coefficient of friction between the cable and the tray, which can vary from near zero with well-lubricated rollers to 0.1–1.0 for unlubricated pulls.

Definition and Importance

The cable tray removal coefficient is essentially the coefficient of friction (COF) used to calculate the pulling force required to remove or install cables in a tray system. It represents the ratio of the force needed to move the cable horizontally over the tray to the normal force pressing the cable against the tray surface ( ). This coefficient is critical for estimating pulling tensions and ensuring safe cable handling.

Factors Affecting the Coefficient

1. Tray and Cable Materials: The type of cable jacket (PVC, XLPE, or armoured) and tray material (steel, aluminum, or coated surfaces) significantly influence friction ( ).
2. Bends and Sheaves: In cable trays with bends, well-maintained sheaves or rollers allow the cable to turn freely, effectively reducing the friction coefficient to near zero. Poorly maintained sheaves can multiply the pulling force, similar to conduit bends ( ).
3. Lubrication: Applying compatible pulling lubricants can lower the COF, especially for heavier cables. Pre-lubrication of the tray or cable is recommended ( ).
4. Temperature: High ambient or cable temperatures can increase the COF for non-metallic jackets, while cold conditions may stiffen the cable and increase resistance ( ).
5. Dynamic vs. Static Friction: The dynamic friction coefficient (for moving cables) is lower than the static friction coefficient (for starting motion). Pulls should avoid stopping and restarting to prevent higher static friction forces ( ).

Typical Values

• Well-lubricated cable on rollers or sheaves: COF ≈ 0
• Standard horizontal tray with minimal lubrication: COF ≈ 0.1–0.3
• Unlubricated or rough surfaces: COF can exceed 1.0 ( )

Practical Application

When calculating the pulling force for cable removal, the COF is used in the tension equations along with cable weight, tray slope, and bend effects. For heavier cables or multiple cables in a tray, the total pulling force must account for cumulative friction and bending around sheaves ( ). Using the effective COF, which considers all field conditions, provides a realistic estimate for planning and safe execution ( ). In summary, the cable tray removal coefficient is not a fixed number but a dynamic, context-dependent value influenced by cable type, tray design, lubrication, temperature, and the condition of rollers or sheaves. Proper assessment ensures safe and efficient cable removal.