How to Make a T1 Crossover Cable
By Richard Asmus
T1 lines carry 1.544 Mbps signals for computer network connections in the immediate area, across town or across the country. T1 cables use four wires: two for the transmit signal and two for the receive. In some network applications, the equipment is so close together that a "crossover cable" just a few feet long makes the connection. The T1 signal transmitted from each of the two units "crosses over" to the receive signal of the other. Use crossover cables to connect T1 servers, private telephone switches (PBXs) or other T1 network devices together.
Cut the cable to the desired length. Strip the outer covering off to expose the eight pairs of wires at each end.
Place the wires into a RJ-45 connector at one end or the cable. Put the white with blue marks into pin 1 and the blue with white marks into pin 2. Place the white wire with orange marks into pin 4 and the orange with white into pin 5. Cut the other wires off at the end of the outer insulation. Some connectors require you to strip the insulation off the wires, but the most convenient make the connection when you make the crimp.
Place the connector in the crimping tool and squeeze the handles until they stop. Remove the connector from the tool.
Place wires into the connector at the other end of the cable. Place the white wire with orange marks into pin 1 and the orange with white marks into pin 2. Place the white wire with blue marks into pin 4 and the blue with white into pin 5. Cut the other wires off at the end of the outer insulation.
Place the connector in the crimping tool and squeeze the handles until they stop. Remove the connector from the tool. Your crossover cable is finished.
- You can buy pre-made T1 crossover cables from some computer dealers, and the price may be less than the cost of a compression tool.
- Cat-5 cable has four twisted pairs of wires using white along with blue, orange, green and brown for color coding. One wire in each pair is mostly white, designating it the "tip" (T) and the other is the "ring" (R). T1 terminology uses "T, R" to designate the transmit pair and "T1, R1" to designate the receive pair.
- Do not split the pairs. Make sure each wire for each direction uses the same color for T and R.
- Cat-5 cable comes with either stranded or solid conductors. Use RJ-45 plugs designated for the type of cable you use.
- Be aware that crossover cables for applications other than T1 also use Cat-5 cable and RJ-45 connectors, but the pin designations are different. Crossover cables for other applications will not work with T1.
Richard Asmus was a writer and producer of television commercials in Phoenix, Arizona, and now is retired in Peru. After founding a small telecommunications engineering corporation and visiting 37 countries, Asmus studied broadcasting at Arizona State University and earned his Master of Fine Arts at Brooklyn College in New York.