General Guidelines For Installing Fiber Optic Cable
Fiber
optic cable may be installed indoors or outdoors using several
different installation processes. Outdoor cable may be direct
buried, pulled or blown into conduit or innerduct, or installed
aerially between poles. Indoor cables can be installed in raceways,
cable trays above ceilings or under floors, placed in hangers, pulled
into conduit or innerduct or blown though special ducts with compressed
gas. The installation process will depend on the nature of the
installation and the type of cable being used.
Installation
methods for both wire and optical fiber communications cables are
similar. Fiber cable is designed to be pulled with much greater force
than copper wire if pulled correctly, but excess stress on the cable
may harm the fibers, potentially causing eventual failure. Particular
care should be taken during installation to prevent kinking the cable
which can harm the fibers.
Since there are so many types of
fiber optic cable and so many different applications, it is hard to
cover each application in detail. However there are some general rules
that should be followed:
Installation Guidelines
Follow
the cable manufacturer's recommendations. Fiber optic cable is often
custom-designed for the installation and the manufacturer may have
specific instructions on its installation.
Check the cable length
to make sure the cable being pulled is long enough for the run to
prevent having to splice fiber and provide special protection for the
splices.
Try to complete the installation in one pull. Prior
to any installation, assess the route carefully to determine the
methods of installation and obstacles likely to be encountered.
Pulling tension
Cable
manufacturers install special strength members, usually aramid
yarn (DuPont Kevlar), for pulling. Fiber optic cable should only be
pulled by these strength members unless the cable design allows pulling
by the jacket. Any other method may put stress on the fibers and harm
them.
Swivel pulling eyes should be used to attach the pulling rope or tape to the cable to prevent cable twisting during the pull.
Cables
should not be pulled by the jacket unless it is specifically approved
by the cable manufacturers and an approved cable grip is used. These
grips are usually tied to the strength members also.
Tight buffer
cable can be pulled by the jacket in premises applications if a large
(~40 cm, 8 in.) spool is used as a pulling mandrel. Wrap the
cable around the spool 5 times and hold gently when pulling.
Do not
exceed the maximum pulling tension rating. Consult the cable
manufacturer and suppliers of conduit, innerduct, and cable lubricants
for guidelines on tension ratings and lubricant use.
When pulling long lengths of cable in conduit or innerduct (up to approximately 3 miles or 5 kilometers in the outside plant,
hundreds of meters in premises cabling), use proper lubricants and make
sure they are compatible with the cable jacket. If possible, use an
automated puller with tension control and/or a breakaway pulling
eye. On very long OSP runs (farther than approximately 2.5 miles
or 4 kilometers), pull from the middle out to both ends or use an
automated fiber puller at intermediate point(s) for a continuous pull.
When laying loops of fiber on a surface during a pull, use “figure-8” loops to prevent twisting the cable.
Bend radius
Do
not exceed the cable bend radius. Fiber optic cable can be broken when
kinked or bent too tightly, especially during pulling.
If no
specific recommendations are available from the cable manufacturer, the
cable should not be pulled over a bend radius smaller than twenty (20)
times the cable diameter.
After completion of the pull, the cable should not have any bend radius smaller than ten (10) times the cable diameter.
Twisting cable
Do
not twist the cable. Twisting the cable can stress the fibers.
Tension on the cable and pulling ropes can cause twisting. Use a swivel
pulling eye to connect the pull rope to the cable to prevent pulling
tension causing twisting forces on the cable.
Roll the cable off
the spool instead of spinning it off the spool end to prevent
putting a twist in the cable for every turn on the spool.
When
laying cable out for a long pull, use a "figure-8" on the ground to
prevent twisting. The figure 8 puts a half twist in on one side of the
8 and takes it out on the other, preventing twists.
Vertical cable runs
Drop vertical cables down rather than pulling them up whenever possible.
Support
cables at frequent intervals to prevent excess stress on the jacket.
Support can be provided by cable ties (tightened snugly, not tightly
enough to deform the cable jacket) or Kellems grips.
Use service loops can to assist in gripping the cable for support and provide cable for future repairs or rerouting.
Use Of Cable Ties
Fiber
optic cables, like all communications cables, are sensitive to
compressive or crushing loads. Cable ties used with many cables,
especially when tightened with an installation tool, are harmful to
fiber optic cables, causing attenuation and potential fiber breakage.
When
used, cable ties should be hand tightened to be snug but loose enough
to be moved along the cable by hand. Then the excess length of the tie
should be cut off to prevent future tightening.
Hook-and-loop
fastener ties are preferred for fiber optic cables, as they cannot
apply crush loads sufficient to harm the cable.
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