For a proper fiber optic cable installation, it is important to obey some rules when installing fiber cables. The following tutorial lists the 7 most important factors to consider.
1. Minimum Bend Radius.
Optical fiber cable installation is as simple as, and in many cases much easier than, installing coaxial or UTP cable in the horizontal. The most important factor in optical fiber cable installation is maintaining the cable’s minimum bend radius.
Bending the fiber cable tighter than the minimum bend radius may result in increased attenuation and broken fibers. If the elements of the cable are not damaged, when the bend is relaxed, the attenuation should return to normal.
The following table shows the minimum bend radius for fiber optic cables under tension and for long term installation. This table is typically specified by cable manufacturers.
|Minimum Bend Radius|
2. Maximum Tensile Rating
The fiber cable’s maximum tensile rating must not be exceeded during installation. This value is specified by the cable manufacturer.
Tension on the cable should be monitored when a mechanical pulling device is used. Hand pulls do not require monitoring.
Circuitous pulls can be accomplished through the use of backfeeding or centerpull techniques. For indoor installations, pull boxes can be used to allow cable access for backfeeding at every third 90° bend.
The following table lists the typical maximum tensile load specified by fiber cable manufacturers.
|Maximum Tensile Load|
|Short Term||Long Term|
3. Maximum Vertical Rise
All optical fiber cables have a maximum vertical rise that is a function of the cable’s weight and tensile strength. This represents the maximum vertical distance the cable can be installed without intermediate support points.
Some guidelines for vertical installations include the following:
- All vertical cable must be secured at the top of the run. A split mesh grip is recommended to secure the cable.
- The attachment point should be carefully chosen to comply with the cable’s minimum bend radius while holding the cable securely.
- Long vertical cables should be secured when the maximum rise has been reached.
4. Cable Protection
If future cable pulls in the same duct or conduit are a possibility, the use of innerduct to sectionalize the available duct space is recommended. Without this sectionalization, additional cable pulls can entangle an operating cable and could cause an interruption in service.
care should be exercised to ensure the innerduct is installed as straight as possible, without twists that could increase the cable pulling tension.
When the cable is installed in raceways, cable trays, or secured to other cables, consideration should be given to movement of the existing cables. Although optical fiber cable can be moved while in service without affecting fiber performance, it may warrant protection with conduit in places exposed to physical damage.
5. Duct Utilization
When pulling long lengths of cable through duct or conduit, less than a 50% fill ratio by cross-sectional area is recommended. For example, one cable equates to a 0.71 inch outside diameter cable in a 1 inch inside diameter duct.
Multiple cables can be pulled at once as the tensile load is applied equally to all cable. Fill ratios may dictate higher fiber counts in anticipation of future needs. One sheath can be more densely packed with fiber than multiple cable sheaths.
In short, for customer premises applications, the cost of extra fibers is usually small when these extra fibers are not terminated until needed. For a difficult cable pull, extra fibers installed now but not terminated may be the most cost-effective provision for the future.
6. Preconnectorized Fiber Cable Assemblies
Of special consideration is the use of preconnectorized cables. Although the use of factory-terminated cross-connect and interconnect jumper assemblies is acceptable, the use of preconnectorized backbone and distribution cable presents special installation techniques.
These connectors must be protected when installing the connectorized end of these cables. Protective pulling grips are available to protect connectors, but the grip’s outside diameter may prevent installation in small innerducts or conduits. The size of the preconnectorized assembly and pulling grip should be considered before ordering factory connectorized cables.
There may also be additional installation requirements imposed on the grip by the manufacturer, in terms of minimum bend radius and tension, that would be the limiting parameters in an installation.
7. Fiber Optic Cable Slack
A small amount of slack cable (20-30 feet) can be useful in the event that cable repair or relocation is needed. If a cable is cut, the slack can be shifted to the damaged point, necessitating only one splice point in the permanent repair rather than two splices if an additional length of cable is added. This results in reduced labor and hardware costs and link loss budget saving.
Additional cable slack (approximately 30 feet) stored at planned future cable drop points will result in savings in labor and materials when the drop is finally needed. Relocation of terminals or cable plant can also take place without splicing if sufficient cable slack is available.