Installation considerations for fiber-optic cable

Installing optical fiber in horizontal cable runs is simple and, in many cases, much easier than installing unshielded twisted-pair cable. The most important factor in such installations is maintaining the cable`s minimum bend radius. Bending the cable more tightly than recommended may result in increased attenuation or broken fibers.

Arlyn S. Powell, Jr.

Installing optical fiber in horizontal cable runs is simple and, in many cases, much easier than installing unshielded twisted-pair cable. The most important factor in such installations is maintaining the cable`s minimum bend radius. Bending the cable more tightly than recommended may result in increased attenuation or broken fibers.

Attenuation is the loss of signal strength as the light pulse travels down the fiber. It is generally caused by stresses on the fiber--either by stretching, bending, or compressing it. These stresses can result from many factors, including careless handling during installation and changes in the fiber`s environment once installed--for instance, expansion and contraction of the cable because of temperature changes.

Therefore, a requirement of fiber-optic cable design is to minimize the loss that may result from cabling and installation. If, for example, the buffer tube and sheath are not damaged during installation, the attenuation in the fiber should return to an acceptable value when a bend in the cable is relaxed. This is why cable manufacturers specify a minimum bend radius for cables under tension, such as when they are being pulled, as well as for long-term installations.

In addition, the cable`s maximum tensile rating must not be exceeded during installation. This value is specified by the cable manufacturer and should be monitored when a mechanical pulling device is used. Hand pulls do not require monitoring the tension on the cable. Long or circuitous pulls can be eased by using backfeeding or center-pull techniques to reduce the tension. For indoor installations, using pull boxes at every third 90o bend allows access to cable for backfeeding.

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