COMPUTER WIRING CAT PAGE
Ethernet CAT 5 UTP Cabling
Category 5 Unshielded Twisted PairEight-conductor data cable (CAT 5 UTP) contains 4 pairs of wires in an unshielded plastic sheath. Each pair consists of a solid color wire and a white and color striped wire. Each of the pairs are twisted together. To maintain reliability on Ethernet, you should not untwist them any more than necessary (1/2 inch maximum).
Wire thickness for CAT 5 UTP is 22 0r 24 AWG (Wire thickness is measured by gauge and represented by the unit AWG, for American Wire Gauge. The higher the gauge number, the thinner the wire.) CAT 5 UTP is capable of transmitting up to 1,000 Mbps (gigabit) when strictly installed to EIA/TIA 568 specifications (Electronics Industry Association/Telecommunications Industry Association). CAT 5 UTP is rated to 100 MHz.
Color Codes for RJ-45 Ethernet PlugThe pairs designated for 10BaseT Ethernet are orange and green. The other two pairs, brown and blue, are unused. The connections shown are specifically for an RJ45 plug. The wall jack may be wired in a different sequence because the wires may be crossed inside the jack. The jack should either come with a wiring diagram or at least designate pin numbers that you can match up to the color code below. A punch-down tool is generally used to install wire onto a wall jack.
There are two wiring standards for these cables, called T-568A and T-568B. They differ only in pin assignments, not in uses of the various colors. The illustration above shows both standards.
Differences Between StandardsWith the T-568B specification the orange and green pairs are located on pins 1, 2 and 3, 6 respectively. The T-568A specification reverses the orange and green connections, so that the blue and orange pairs are on the center 4 pins, which makes it more compatible with the telco voice connections.
T-568B is generally used as the standard CAT 5 pin-out.
Pin Number DesignationsHere are the pin number designations for both standards:
Note: Odd pin numbers are always the striped wires.
Straight-Through v. CrossoverIn general, the patch cords that you use with your Ethernet connections are "straight-through," which means that pin 1 of the plug on one end is connected to pin 1 of the plug on the other end (for either standard). The only time you cross connections in 10BaseT is when you connect two Ethernet devices directly together without a hub or connect two hubs together. Then you need a "Crossover" patch cable, which crosses the transmit and receive pairs. An easy way remember how to make a Crossover cable is to wire one end with the T-568A standard and the other with the T-568B standard. It is a good idea to use a distinctive cable color for crossover patch cords.
Step-By-Step Wiring Instructions
Note: A punch-down tool is generally used to install wire onto a wall jack. The wall jack is normally color-coded. Place un-stripped wire on the clip and press down with punch-down tool. The tool automatically puts wire in place and trims off the excess.
Common Installation MistakesStrict adherence to EIA/TIA 568 installation standards is essential to successful transmission at 100 Mbps over CAT 5 UTP. Because a less-than-perfect installation will probably transport 10 Mbps traffic without problem, noncompliant installations may not surface until upgrades to 100 Mbps network architectures are attempted. Among the most common installation mistakes are the following: