Network Building: Twisted-Pair Cable Pinouts

A pinout is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions. Each pair of wires in a twisted-pair cable is one of four colors: orange, green, blue, or brown. The two wires that make up each pair are complementary:

One is a solid color, the other is white with a stripe of the corresponding color. For example, the orange pair has an orange wire and a white wire with an orange stripe. Likewise, the blue pair has a blue wire and a white wire with a blue stripe.

When you attach a twisted-pair cable to a modular connector or jack, you must match up the right wires to the right pins. You can use several different standards to wire the connectors. To confuse matters, you can use one of the two popular standard ways of hooking up the wires. One is known as EIA/TIA 568A; the other is EIA/TIA 568B, also known as AT&T 258A.

It doesn’t matter which of these wiring schemes you use, but pick one and stick with it. If you use one wiring standard on one end of a cable and the other standard on the other end, the cable won’t work.

Pin Connections for Twisted-Pair Cable
Pin Number Function EIA/TIA 568A EIA/TIA 568B
AT&T 258A
Pin 1 Transmit + White/green White/orange
Pin 2 Transmit – Green Orange
Pin 3 Receive + White/orange White/green
Pin 4 Unused Blue Blue
Pin 5 Unused White/blue White/blue
Pin 6 Receive – Orange Green
Pin 7 Unused White/brown White/brown
Pin 8 Unused Brown Brown

10BaseT and 100BaseT actually use only two of the four pairs, connected to pins 1, 2, 3, and 6. One pair is used to transmit data, and the other is used to receive data. The only difference between the two wiring standards is which pair is used to transmit data and which pair is used to receive data.

In the EIA/TIA 568A standard, the green pair is used to transmit and the orange pair is used to receive. In the EIA/TIA 568B and AT&T 258A standards, the orange pair is used to transmit and the green pair to receive.

If you want, you can get away with connecting only pins 1, 2, 3, and 6. However, you should connect all four pairs as indicated above.