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FIBER OPTIC CABLE INSTALLATION

When installing fiber optic cable, there are some important factors that need to be taken into consideration. Below are the top 7 we recommend for safe and effective fiber optic installation.


MINIMUM BEND RADIUS

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 table to the left shows the minimum bend radius for fiber optic cables under tension and for long term installation.


MAXIMUM TENSILE RATING

The fiber cable's maximum tensile rating must not be exceeded during installation and kept to the value specified.

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 back-feeding or center-pull techniques. For indoor installations, pull boxes can be used to allow cable access for back-feeding at every third 90° bend.


The table above shows typical maximum tensile load ratings.


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 the 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.

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.

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.


FIBER OPTIC CABLE SLACK

A small amount of slack cable (20-30 feet / 8 mtrs) 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 / 8 mtrs) 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.

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