Markets: Cable Management
Installing cables may look like a simple procedure, but there are several factors that installers are considering behind the scenes. Bend radius, tensile rating, cable slack, cable protection and conduit fill utilization are just a few of these considerations.
A cable’s bend radius may be the most important aspect to keep in mind. Copper cable consists of conductors that are twisted together, so excessive bending or twisting can disrupt the careful geometry of those twists. Bending, twisting or stretching is also damaging to a fiber cable, but for different reasons. The fiber cable will instead be damaged by micro cracks that result in broken fibers or attenuation (the loss of signal strength throughout the cable). Cable manufacturers always provide a minimum bend radius for cables under tension. When you’re pulling cables, following the minimum bend radius will ensure no damage is done to the cables and prevent the need for a reinstallation.
Another factor to keep in mind while pulling cables is tensile rating. Like bend radius, tensile rating is specified by the manufacturer and refers to how much tension is allowed to be placed on the cable. Installers using mechanical pulling devices should monitor the tensile rating during installation and ensure the number specified by the manufacturer is not exceeded; otherwise, the cables may be damaged. Long pulls can use certain pull techniques such as backfeeding or center-pull to ease the tension on the cable.
It’s recommended that installers leave some (20-30 feet) slack cable to reduce labor and hardware costs. If a cable repair or relocation is needed, the slack can be shifted to the damaged point. This slack cable can be stored at planned future cable drop points to allow relocation of terminals to take place without splicing. This small consideration during installation can save a significant amount of time in the future.
Installers should consider the integrity of the cables not only during installation but also after. Depending on where a cable is being installed, outside protection may be necessary to keep cables safe, and installers should consider whether a conduit or duct is necessary based on the installation circumstances. Underground installations, for example, almost always require a conduit when cables are installed. One cable per conduit is the standard, except with a product such as Vis™ Divide, which is a rigid segmented conduit that allows for up to three cables inside one conduit. If future cable pulls are a possibility, Vis Divide also provides an available pathway if all segments are not utilized. Regardless of the application, protecting the cables from physical harm after installation is a must.
Proper conduit fill is imperative for efficient space utilization during cable installations. Conduit fill refers to the amount of a conduit’s cross-sectional area that is occupied by cable(s) and is based on the cable’s outside diameter (OD) and the conduit’s inside diameter (ID). Most conduits require a fill ratio of less than 50 percent and only permit one cable to be pulled per conduit. Vis Divide, however, allows a fill ratio up to 70 percent and can hold up to three cables per conduit. Utilizing all the conduit space and choosing the correct conduit size should always be a consideration, especially when capacity is a factor.
Something as seemingly simple as a cable pull is only successful when special consideration is given before, during and after installation. To dig deeper into conduit installation tips, read this post on Vis Divide installation methods.