for a standard four-pair copper cable. The wires are relatively thin (between 22
and 24 gauge). The cables are twisted into a pair to reduce crosstalk (“cou-
pling” of the pairs or interference from an adjoining cable) as well as interfer-
ence from electrical and mechanical sources. Each pair has a different number
of twists relative to the other pairs in the cable to further reduce crosstalk. This
construction is usually referred to as unshielded twisted pair.
The twisted pairs can also be “shielded,” creating shielded twisted-pair
cable. While the use of shielded twisted pair is popular in some countries
and has some technical advantages, it is more labor intensive during installa-
tion because of the grounding required and is typically not used in a structured
cable infrastructure.
Unshielded twisted-pair cables are relatively inexpensive and there are a
large number of technicians qualified to install the cable. The cable standards
guarantee performance of the cable over 90 meters (295 feet). Categories of
unshielded twisted pairs are based on the bandwidth, or information-carrying
capacity, of the cable.
The most recent categories of unshielded twisted-pair are Category 5e and
Category 6. Category 5e cable is specified up to a bandwidth of 100 MHz
(Hz is a unit of frequency equal to one cycle per second). The Category 6
Figure 2.4 Twisted pair copper cable.
14 Smart Building Systems for Architects, Owners, and Builders