Copyright Goodheart-Willcox Co., Inc. 79 Chapter 2 Network Media—Copper-Core Cable Ground A ground occurs when a conductor connects to the earth through a continuous path. Grounds typically occur where the conductor’s insulating jacket is torn and the copper conductor makes contact with conduit or any other metal surface that is grounded. When a ground occurs in a network cable, all data is prevented from reaching its destination. Reversed, Crossed, and Split Pairs Reversed, crossed, and split pairs commonly occur when technicians install connec- tors on twisted-pair cables in the fi eld. It is very easy to misconnect individual wires when installing an RJ-45 connector or when terminating a twisted-pair cable in a punch down block. Th e misconnection may go unnoticed until after the network sys- tem is installed and a computer has a problem accessing the network. Study the examples in Figure 2-37 of reversed, crossed, and split pairs. A reversed pair occurs when two pairs of a cable assembly have reversed two con- nections, Figure 2-37B. For example, a blue pair has reversed pin connections with a green pair. A crossed pair occurs when one of each of the two cable pairs has be- come part of the other pair’s connection. In Figure 2-37C, one conductor of the blue pair is connected as one conductor of the green pair. One conductor of the green pair is connected as one conductor of the blue pair. A split pair occurs when two pairs of conductors are reversed in connection with another pair. In Figure 37D, a complete pair of blue conductors has been reversed with connections intended for the green pair, and the green pair has taken the position intended for the blue pair. Electronic cable testers are designed for testing a cable for the possibility of opens, crossed pairs, split pairs, and reversed pairs. You will use a cable tester often in the fi eld when troubleshooting network communication problems. Figure 2-38 shows a cable tester. Tech Tip Remember, a short occurs between two conductors, a ground occurs between a conductor and the earth. The connection to the earth is usually provided by a metallic enclosure, such as the metal pipe used to carry network ca- bles, or exposed metal building parts, such as I-beams or drop ceiling channels. 5.3 NET + – Open Splice point Switch Lamp Power source Figure 2-36 In this circuit, there is a break in the wiring at the splice point. When the switch is closed, the lamp does light. This condition is called an open. Goodheart-Willcox Publisher