Summary

26 IT Essentials: PC Harware and Software Companion GuideFigure 8-16Twisted-Pair CablingWhen electricity flows through a copper wire, a magnetic field is created around the wire.A circuit has two wires, and in a circuit, the two wires have oppositely-charged magneticfields. When the two wires of the circuit are next to each other, the magnetic fields canceleach other out. This is called the cancellation effect. Without the cancellation effect, yournetwork communications become slow because of the interference caused by the magneticfields.The two basic types of twisted-pair cables are as follows:■■Unshielded twisted pair (UTP) is cable that has two or four pairs of wires. This type ofcable relies solely on the cancellation effect produced by the twisted-wire pairs thatlimits signal degradation caused by electromagnetic interface (EMI) and radio frequencyinterference (RFI). UTP is the most commonly used cabling in networks. UTPcables have a range of 328 feet (100 m).With shielded twisted pair (STP), each pair of wires is wrapped in metallic foil to bettershield the wires from noise. Four pairs of wires are then wrapped in an overallmetallic braid or foil. STP reduces electrical noise from within the cable. It alsoreduces EMI and RFI from outside the cable.Although STP prevents interference better than UTP, STP is more expensive because ofextra shielding. It also is more difficult to install because of the thickness. In addition, themetallic shielding must be grounded at both ends. If it’s improperly grounded, the shieldacts like an antenna, picking up unwanted signals. STP is primarily used outside NorthAmerica. STP cables also have a range of 328 feet (100 m).