Information Technology Reference
In-Depth Information
Prewire and Postwire Methods.
Prewiring may be accomplished with actual cable
runs or with a combination of pull strings and late-stage cable runs. If the actual
cable is used for the prewire, it must be installed at the stage between wall support
installation and wall sheathing attachment. This is often referred to as the
rough-in
stage
. With the wall supports in place, the cable is run from each wiring closet to
each served station outlet box or ring and either coiled inside the box or secured to
the ring. After the wall sheathing is in place, and usually after the wall has been fin-
ish-painted or papered, each cable is trimmed to working length and terminated in
the jack. The assembled outlet is then mounted in the box or ring.
Using the actual cable in the rough-in stage can present some problems if you
are planning a full Category 5e or Category 6+ installation.
The cable is left exposed and subject to damage by others during the construc-
tion. In addition, you must coil up the wire very carefully to avoid the sharp bends
and kinks that can disturb cable performance at this category of operation.
Another technique is to leave a pull string in the wall during the rough-in
stage—placed in a hollow wall or inside a riser that connects to the outlet box.
Outlet boxes may have vertical risers (conduit) that run from the top of the box,
through the wall's top plate, and half a foot or so into the plenum space above the
ceiling grid. A pull string may be run through the conduit to assist in cable installa-
tion. If a mounting ring is used for the outlet, a pull string is particularly conven-
ient. The opposite end of the string should be secured to anything above the top
plate, where it will be visible to the cable installer. After the wall construction is fin-
ished, and preferably before the ceiling tiles are in place, the cables are run from the
wiring closet to each outlet's pull string, attached, and pulled into the outlet, where
they may be terminated.
Pull strings and conduit are effective ways to run cable into difficult outlet
locations, such as below windows or in columns. Cable may also be coiled and
secured above a planned outlet location for later pulling into an outlet box or ring.
Again, if you are planning a Category 5e/6 installation, be careful not to put sharp
bends or kinks into the cable.
Tie wraps may be used sparingly, but should not be overly tightened.
You should take care when running your cable into an outlet box so that you
do not slice through the cable jacket. Metallic boxes often have sharp edges as a
result of the way they are manufactured. These sharp places can cut into the cable
and short some of the wires. Mounting rings may present other hazards to cable,
such as the sharp screws that are used to secure some of the rings to the wall
sheathing.
