Information Technology Reference
In-Depth Information
special channels for telephone and computer wiring that is separated from the AC
power wiring channels. Caution should be used when sharing the power wiring
channel with data cabling. Not only is there a potential safety concern from having
the LAN wire so close to power wire voltages, but there may be performance prob-
lems, particularly for Category 5e performance. Some guidelines specify a 2-in or
more separation from power wires, while others specify a greater distance. In addi-
tion, local and national installation codes generally prohibit low-voltage wiring
from being installed in the same conduit as power wires. Some local authorities may
consider the open wiring channels of modular furniture to be in fact a conduit and
therefore subject to this rule. Modular channels with a divider avoid this problem.
Horizontal wiring is specified according to performance categories defined in
TIA/EIA-568-C. Both cable and connecting hardware (jacks and plugs) must meet
performance guidelines appropriate for their use. Not all cable or components meet
the minimum standards required for LAN use.
One of the factors affecting performance in outlet jacks is the method of wire
termination. The station cable connects to the jack by means of either screw termi-
nals or some sort of insulation-displacement termination. Screw terminations were
acceptable in Category 3 installations, but are prohibited in Category 5e or 6 instal-
lations, because of performance constraints. Category 3 is adequate for 10- or 16-
MHz bandwidth networks, Category 4 for 20 MHz, and Category 5e for 100 MHz.
For the most part, no networks require Category 4 specifications, although it was
used if you desired a “high-grade” Category 3 installation. Some references suggest
Category 4 for Token-Ring networks, but the legacy standards required only
Category 3. Category 5e is now the minimum specification.
Insulation-displacement terminations use a split metal contact upon which the
insulated wire is forced, thereby cutting through the insulation and making metal-to-
metal contact with the copper wire. Several types of insulation-displacement connec-
tors (IDCs) exist, including modular snap-together IDC jacks, modular 110-type IDC
jacks, and older 66-type IDC jack plates. Except for the 66-type jacks, all are com-
monly available in models that are certified to Category 5e performance standards.
Category 5e 66-blocks do exist, but the installer may have difficulty maintain-
ing the required twist all the way to the termination point.
From the workstation outlet jack, the horizontal station cable is run to the des-
ignated wiring closet. This cable run is designed to be within (possibly well within)
the 90 m maximum specified by the standards. It may be routed with other individ-
ual station cables in wiring trays, through support rings over support beams or
frames, through firewalls, or even in conduit. If you have special performance crite-
ria, such as Category 5e or 6, you should take precautions to avoid fluorescent light
baluns (the transformer in each light fixture), electrical wiring, heavy equipment
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