Twisted Pair Definition

Twisted pair refers to two independently insulated, thin diameter, copper wires that are twisted loosely around each other.

This configuration is used in order to reduce electromagnetic interference from other twisted pairs in the same cable and from other sources. It works by providing both wires with nearly equal exposure to any source electromagnetic or electrostatic interference.

Various types of twisted pair cable are available, differing with regard to the number of pairs within each cable, whether each wire is composed of a single conductor or many thin strands, the size (i.e., gauge) of the wire, and whether the cables have electromagnetic shielding (STP) or not (UTP).

The stranded wire, which is the most common, is very flexible and can be bent repeatedly without breaking. Solid wire cable has less attenuation (i.e., reduction in signal strength) and thus allows transmission over longer distances, but it is less flexible and cannot be bent repeatedly without breaking. Common cable sizes include two, three, four, 25, 50 and 100 pairs.

Twisted pair cable was invented by Alexander Graham Bell, who was granted a patent for it in 1881. It was originally used for telephones, but it has also become widespread for local area networks (LANs).

LANs originally used coaxial cable, which contains metal shielding surrounding the wires in the center of the cable. However, twisted pair cable offers the important advantages of lower cost, greater flexibility and greater ease of use.

Category 5 cable (commonly known as Cat 5), now the cable most commonly used in high speed LANs, contains four twisted pairs and is terminated with RJ-45 connectors.

Created September 28, 2005.
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