Ethernet cables use different categories to represent the quality of the cable. The original Ethernet standards used Category 3 cables, which were shared with traditional phone lines. Eventually, the Category 5 cable standard was established, which used eight wires. Since that time, newer cable categories have been added to allow for faster communications, with Category 5e and 6 being common, as of 2011. You can check an Ethernet cable with an Ethernet testing tool.
Connect one end of the Ethernet cable into one of the Ethernet ports on the Ethernet cable tester.
Connect the other end of the Ethernet cable into the other Ethernet port on the Ethernet cable tester.
View the diagnostic lights on the tester. Ethernet cables have four pairs of wires inside. There are four lights on the tester, each representing a pair of wires. All four lights should be turned on to signify that the cable is healthy. If any lights are not lit, it means that either the cable itself or one of the connectors at the end of the cable are faulty.
There are two types of Ethernet cable testers -- local and remote. A local tester is a single box with two Ethernet ports on it. A remote tester is two separate boxes, each with a single Ethernet port. The testing process is the same for both types of cable testers, but a remote tester allows you to test established cable runs in addition to regular individual cables.