Ethernet RJ45 Wiring Reference

The TIA/EIA 568-A standard which was ratified in 1995, was replaced by the TIA/EIA 568-B standard in 2002 and has been updated since. Both standards define the T-568A and T-568B pin-outs for using Unshielded Twisted Pair cable and RJ-45 connectors for Ethernet connectivity.

TWISTED PAIR ETHERNET WITH RJ-45 CONNECTOR

If you hold the RJ-45 connector facing you (as if you were going to plug it into your mouth) with the lock tab behind, then the pins are numbered 1 to 8 from left to right. The pin usage is as follows:

       Pin Number              Assignment
       ----------              ----------
       1                       Output Data (+)
       2                       Output Data (-)
       3                       Input Data (+)
       4                       Reserved for Telephone use
       5                       Reserved for Telephone use
       6                       Input Data (-)
       7                       Reserved for Telephone use
       8                       Reserved for Telephone use

CLIP FACING DOWN - This is how I wire the connector on twisted pair ethernet: Three (3) and six (6) must be a twisted pair.

 T568B RJ 45 Std                     Cross Over Cable        T568A RJ 45 (less common)
 ---------------                     ---------------         ---------------
 1. White Orange                     1. White Green          1. White Green
 2. Orange                           2. Green                2. Green
 3. White Green    (twisted pair)    3. White Orange         3. White Orange    (twisted pair)
 4. Blue                             4. White Brown          4. Blue
 5. White Blue                       5. Brown                5. White Blue
 6. Green          (twisted pair)    6. Orange               6. Orange          (twisted pair)
 7. White Brown                      7. Blue                 7. White Brown
 8. Brown                            8. White Blue           8. Brown

• A Standard T568A or T568B cable are identical on both ends.
• Standard T568A or T568B cables are often used as "patch cords."
• A crossover cable is used to connect two network devices in the absence of a network hub.
• The crossover cable basically switches the orange and green wire sets.
• Never untwist more than ½ of the tiny wires to reduce any occurrence of crosstalk.
• Kinks in the network cable, or running the cable near devices that produce RF noise may negatively impact network performance.
• The blue and brown wire pairs on pins 4, 5, 7, and 8 are not used in either standard.
• Do not exceed 330ft in a single cable run for 100BaseTX fast Ethernet.
• Do not exceed 980ft in a single cable run for 10baseT Ethernet.

Ironically, the wires on pins 4, 5, 7, and 8 could be cut and completely omitted from the connectors. They are not used in 10BaseT or 100Base-TX.

Now days many telcos are using twisted pair ethernet, Cat 5 and above, for all telephone wiring in home and office. See our Telephone RJ11 Wiring Reference.

For the T568B standard, which is the most common used in the United States, be sure to observe which way you are holding the cable in your hand when you line up the colored pairs. Some people inadvertently cross wire (not cross-over) their network cable not because they didn't have the colors in the correct order, but because they were holding one end facing upward, and the other facing downward. See illustration below:

Always hold the cable upward with the lock tab facing behind and cable facing up. Slide the RJ45 connector down onto the colored pairs carefully so they are not misaligned both in color and evenness of cut length on top where they will rest against the inside slots of the RJ45 connector.