by: Dean Novosat
There are two wiring standards for network cabling. T568A and T568B are the two standards for the RJ-45 or 8-position modular connector, permitted under the TIA/EIA-568-A wiring standards document. The only difference between T568A and T568B (also known as Weco, AT&T 258A) is that the orange and green wire pairs (pairs two and three) are interchanged. How to decide which wiring pattern to use:
1. Does the job specification call out a wiring pattern?
2. Does the customer/end user have a preference for T568A or T568B?
3. Have patch panels already been purchased for the job? If so, they will probably be either T568A or T568B. The jacks should be wired to the same pattern as the panels.
4. Are you adding on to an existing wiring plant? If so, your new wiring should match the existing wiring.
If none of the factors above apply, either T568A or T568B may be used. It is important to ensure that the workstation connectors and the patch panels are wired to the same pattern. T568B is commonly used in commercial installations, while T568A is prevalent in residential installations. For these reasons, we almost always use T568B for unspecified installations.
One bonus is that most networking equipment presently on the market have wiring diagrams for either T568A or T568B. Since the difference is only the switching of two pairs of wires, it is easy enough for manufacturers to print both standards on their hardware. For example, a patch panel that is labeled for T568A/T568B will usually have the color-coded wiring diagrams above and below the actual punchdown. One will typically be labeled T568A and the other T568B. This type of hardware is preferred by installers due to its flexibility.