Unshielded Twisted Pair (UTP)
has been designed for use in voice applications and local area networks.
Because of the comparatively low cost, this cable is widely used and is
available in several different performance categories (Categories 3, 4, 5
and 6). Over 99% of our copper installations are UTP versus shielded twisted
pair (STP), which is rarely used.
Electromagnetic interference is present in all types of cabling to some
degree. There are two basic types of electromagnetic interference (EMI) that
cable engineers worry about-electromagnetic emissions and electromagnetic
immunity. Emissions refer to energy that is radiated by the cable, and
immunity is the ability of the cable to reject outside signals. In local
area networks (LANs), failure to properly manage EMI can have an adverse
effect on the integrity of the signal being transmitted.
In an unshielded cable, careful design of the cable and the associated
electronic equipment results in a "balance" of the currents in the two
conductors of a pair. That is, the currents in the two conductors are equal
in magnitude but flowing in opposite directions. Proper installation and
termination of the cable is also critical to maintaining this balance. In a
balanced system, there is very little radiation of EMI since the external
field from one conductor is effectively canceled by the external field from
the other conductor of the pair.
Generally, the more twists per foot of cable, the better the cable is
electrically balanced. Category 5 cable has more twists per foot than
Category 3 or 4 cables and, therefore, offers better protection from EMI
problems.