Electrical wire installers know how to pull cable. The basic approach to pulling fiber optic cable differs little from the techniques used to pull copper or aluminum. However, just as aluminum responds differently than copper when
pulled, fiber has its own idiosyncrasies.
The first step in pulling cable is to measure and cut the material. Inaccurate measurements are a disaster in fiber cable installation. Splices are much more critical with fiber than with metal cable because a minimum loss budget must be maintained and splices cause loss. Thus, assumptions and guess work are simply not allowed.
The physical characteristics of fiber cable must always be borne in mind during the installation process. The two characteristics that are particularly important during the installation process are tensile stress (pulling load) and bending radius.
The glass fiber within the cable is fragile, and although the cable has been designed to protect the fiber, it is more easily damaged than metal cables and requires greater care during the process of cable pulling. You simply cannot afford to break fiber cable during the pulling process.
Damage to cable can come in many forms. The most common form of damage, a broken fiber, is also the most difficult to detect. In addition to fracture, fiber can be cracked from too much tension. As a result, no gorillas should be allowed on the cable installation crew.
Although the optical cordage may outwardly resemble copper cordage, the two are significantly different. A failure of optical cordage may occur when improper methods of pulling and despooling are employed. Pulling the outer jacket will cause a compression of the optical fiber and cause significant attenuation increase. This condition once initiated is usually irreversible. One should also avoid cable twist when despooling fiber optic cable to prevent stressing the fibers.
Longitudinal force on the jacket can cause temporary elongation and subsequent fiber compression. Therefore, cable should be reeled off the spool, not spun over the edge of the spool. This will eliminate cable twist, which will make coiling much easier.
When unreeling the cordage, tension should be applied only to the strength member. The strength member and buffered fiber do not stretch. If the outer jacket is used to unreel the cordage from the spool, the resulting shock tension on the outer jacket will allow the jacket to stretch momentarily. The jacket will then return to its normal state. Therefore, the fiber and strength member may be compressed in the retraction of the outer jacket. This will cause macrobend attenuation in the cable.
The pulling force must be kept below a designated limit for the specific cable being installed. This is usually 600 pounds for outside plant (OSP) cable and 300 pounds or less for other cables. The pulling force must also be kept uniform.
Most fiber cable cannot handle high impact loads, so the cable should not be jerked. Included within the cable is a strength member, which is purposely placed there to facilitate installation. This member, not the glass fiber, must always be used when tension is to be placed on the cable.
When using power equipment to pull OSP cable, tension monitoring equipment or breakaway swivels must always be used. Power equipment must never be used on inside fiber because the allowable pulling force is so small.
In order to avoid quality problems after installation, as well as to eliminate disputes that could arise over responsibility for damaged cable, testing of cable prior to installation is recommended. Preinstallation testing becomes particularly important under certain circumstances, such as installation under especially difficult conditions, expensive cable being installed, or an unknown supplier or manufacturer of the cable.
Preinstallation testing need not be complex or time-consuming. If the cable shows no signs of damage, it can be tested with a continuity tracer. If all fibers
transmit light, it is highly likely to be good cable. If there is even a hint of possible damage to the cable, it must be tested or outright rejected.
Postinstallation testing of cable (preceding termination) is recommended if any abnormal circumstances were encountered during the installation process.
Examples of such abnormal circumstances might include exceeding the allowable pulling tension during the pull or sheath damage observed during or after the pull. Any time there is a possibility of damaged cable, the sooner it is detected and remedied the better.