Information Technology Reference
In-Depth Information
TABLE 5.4
Color Code for 4-Pair Cable Pairs
Primary Color
Secondary Color (Stripe)
Pair #
Ring
Tip
1
Blue
White
2
Orange
3
Green
4
Brown
erly. The color code for 4-pair LAN cables is shown in Table 5.4. Each pair of the
cable has complementary colors. For example, pair 1 wires are coded white-blue
and blue-white. The white-blue wire is a white wire with a blue stripe at intervals
along the insulation of the wire. (The stripe is sometimes called a tracer .)
Conversely, the blue-white wire is a blue wire with a white stripe. In a 4-pair cable,
white will be the common color of all the wires, and the white wire will always be
numbered (or punched down) first. Each pair of a 4-pair wire may be referred to by
its color that is unique from the other three pairs. Thus, the “blue” pair contains the
white-blue and the blue-white wires, while the “green” pair contains the white-
green and green-white wires.
Color-coding and proper termination of each wire color is very important in
LAN wiring because the signals are polarity sensitive; reversing a pair will cause a
failure. The polarity of each pair is often referred to as tip and ring , which stems
from the days of telephone plug-boards used to route calls. The switchboard plug
consisted of three contact areas, referred to as the tip, ring, and sleeve, much like a
modern stereo plug. The primary color was wired to the ring and the secondary to
the tip. The sleeve was used for grounding.
The 25-pair jumper cable is another common cable that may be found in some
LAN installations. The color code for 25-pair cables is shown in Table 5.5.
Although 25-pair and larger bulk pair cabling is often used in telephone wiring,
ordinary telephone cabling is not appropriate for today's very high-speed data rates.
It can function at Category 3 as a multi-pair jumper at short distances, such as
between a patch panel and a connectorized punchdown block (both with 50-pin
telco jacks). If 25-pair cable is used in a LAN application, it should have the proper
twists-per-foot as cable for Category 3. Some manufacturers offer 25-pair jumpers
that are said to meet Category 3 or Category 5e, but you should use caution if your
ultimate application will need to support 100 Mbps or higher data rates. Placing
multiple 100 Mbps circuits within the same 25-pair sheath may cause excessive
crosstalk, resulting in excessive error rates or even link failure. The TIA is working
 
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