To help ensure the safety and longevity of your installed cables, here are some key cable mechanical properties to take note of for a successful installation.
• Cable Bending Radius
• Maximum Pulling Tension
• Sidewall Pressure
Cable Bending Radius
The cable bending radius is the minimum radius a cable can be bent to without damaging it. The smaller the bending radius, the greater the flexibility of the material. Knowing your cable's minimum bending radius will help prevent damage during installation. Should you need a reference table and an example of how it is calculated, please refer to our article here.
To prevent over bends in cables, we also have the following recommendation on how a cable could be fed during your setup process.
If you are planning to lay your cables overhead, onto a tray for instance, we recommend mounting cable drums on jacks or cable stands in the orientation so that the cable can be pulled from the top. This is the default recommended orientation for pulling cables rather than from the underside; to prevent the cable from potential damage due to over bending or friction against the ground, especially when there are possible sharp objects such as rocks or nails on site.
Setup for overhead
However, if you are installing the cable in a duct close to the ground, we recommend pulling the cable from the underside instead, taking care to place cable rollers to help support your installation and to prevent damage to your cable sheath.
Setup for duct close to floor
Setup for pulling around bends
For pulling around bends, use sheave assemblies that exceed the minimum bending radius. Pulleys must be positioned to ensure that the effective curvature is smooth rather than polygonal.
Maximum Pulling Tension
When installing larger cables, it is advised to use a cable pulling grip attached to the leading end of the cable’s metallic conductor.
Where pulling attachments are used on the cables, they should be covered with protective tape to prevent scoring of the cable trays, cable ladders, and installation pulleys.
Use a dynamometer to ensure that the cable’s maximum pulling tension based on the manufacturer's recommendation is not exceeded.
Table 1: Permissible Maximum Pulling Tension (Kgf)
*Tip: The cable should be pulled at a constant speed. Drums with a long length of cable should not be allowed to rotate too rapidly as the overrun can cause cable kinks and damage if the pulling is suddenly slowed or stopped.
Side Wall Pressure
Side wall pressure is the tension that the cable experiences as it is pulled through a curved section. This is determined by both the pulling tension exerted on the cable as well as the bending radius limitation of the cable. To prevent damage, it is important to keep the side wall pressure below the 500 Kgf/m maximum permissible side wall pressure.