Cat-5 cable, sometimes called Ethernet cable, is short for Category 5 cable, a current industry standard for network and telephone wiring. This type of cable is unshielded wire containing four pairs of 24-gauge twisted copper pairs, terminating in an RJ-45 jack. If a wire is certified as Cat-5 and not just a twisted pair wire, it will have this designation printed on the outside.
The outer sheath of this type of cable can come in many colors, with bright blue being quite common. Inside, the twisted pairs are also sheathed in plastic with a standard color scheme: solid orange, blue, green and brown wires twisted around mates that are white and striped with a solid color. The twisted pairs reduce interference and crosstalk, and they should be left twisted except at the termination point. Some experts recommend untwisting only 0.5 inch (12.7 mm) of the pairs to strip and make connections. Cat-5 cable can be purchased off a spool in varying lengths, or bought pre-cut to standard lengths with RJ-45 jacks already attached.
Cat-5 replaces Cat-3 cable, which could only carry data at speeds up to 10 megabits per second (mbps), while the newer standard cable supports data speeds of 100 mbps or more. It can also reach 300 feet (100 meters), and aside from networks and telephones, it can be used for many other purposes. Cat-5e is enhanced cable that supports 1,000 mbps or gigabit Ethernet, or it can be used with 100 Base-T networks for long-distance runs of 1,150 feet (350 meters). This type of cable meets a specific standard referred to as "EIA/TIA 568A-5," which should be stamped on the outer sheath.
Among Cat-5 cables, there are three different configurations for pinouts, or wiring of the RJ-45 connectors. Various network devices use one of the three, which are referred to as straight through, crossover and roll-over.
The cable that runs from a computer to a switch will be a straight through cable, for example. If two PCs or two switches are connected, a crossover cable would be used. A roll-over cable will connect a PC to a router. More recent devices, however, can detect the type of cable being used and route signals accordingly.
