LAN Wiring

There are typically three types of wiring used in LAN systems: twisted pair, coaxial cable (coax), and fiber. Of these, twisted pair is dominant for several reasons: ease of installation, availability, cost, and speed as a function of relative cost.

Twisted pair comes in a variety of “categories” and is either shielded twisted pair (STP) or unshielded twisted pair (UTP). UTP is the less expensive and the most widely used. STP has an outer copper or foil conductor located just beneath the out sheath of the wire. In areas where there is a significant incidence of electromagnetic interference (EMI), such as around factory floor machinery or hospital radiological and medical imaging equipment, STP is used.

Twisted pair wire is classified by categories that relate to the data transmission speed at which the wire is capable of passing data. For each category there are manufacturing specifications such as wire quality, insulation characteristics, and number of twists per inch. Generally, the higher the number of twists, the higher the data transmission rate can be.

Routinely LAN cable is four-pair (eight conductors) even though most data communication systems (such as Ethernet) only require 2 pairs (transmit and receive pairs). It is installed with all conductors terminated on each end into patch fields, hub equipment, or office wall plates (jack fields). From the office wall jack the typical PC or peripheral device is connected to the LAN via a wall cord that is also four-pair terminated in RJ-45 modular connectors. Most offices are wired for multiple network connections and in many cases the voice and data wiring is installed together and to the same cable specification (e.g., category 3 and above).