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Appendix D: Making a Correct UTP Cable
Appendix D. Making a Correct UTP Cable
Twisted-Pair Cables: Unshielded twisted-pair cable is used for
BASE-T applications because it is inexpensive, easy to use, and
has excellent noise-canceling capabilities. A minimum of two
pairs of twisted-pair wire are required for each computer that
connects to the local area network:
• One pair of twisted-pair wire to transmit data.
• One pair of twisted-pair wire to receive data.
There are exceptions. 100BASE-T devices (called “T4”) require
four pairs of wires. Also, Gigabit devices (1000 Mbps) require
four pairs. In both cases, two pairs are used for transmit and two
for receive.
As mentioned above, twisted-pair cable has separate pairs of
wires twisted together to minimize crosstalk. If a wiring error is
made and one pair of wire is “split” with another (“split pairs”),
the excess crosstalk will most likely keep the link from operating
properly.
To make a proper cable, first choose a twisted-pair cable that
is adequate for your application. For instance, CAT5e cable for
100-Mbps and 1000-Mbps applications. Use solid-core wire
when pulling inside a wall. Use stranded cable (“patch cable”)
for jumpers.
• Remove the outer jacket of the twisted-pair cable, exposing
about a 6 feet of wire on each end of the cable.
• Each pair of wire must be twisted together (after crimping, the
wire should be twisted right up to the connector).
• Do not make the number one wiring mistake: “Split pairs” (a
wire from one pair is swapped with a wire from another pair).
• To minimize mistakes, use a standard color code throughout
your project. See the following page for the correct connector
pin numbers associated with each BASE-T pair.