ANSI/TIA -568-C Wiring Schemes T568A and T568B ANSI/TIA-568-C does not sanction the use of the USOC scheme. Instead, two wiring schemes are specified, both of which are suitable for either voice or high-speed LAN operation. These are designated as T568A and T568B wiring schemes.
Both T568A and T568B are universal in that all LAN systems and most voice systems can utilize either wiring sequence without system errors. After all, the electrical signal doesn’t care if it is running on pair 2 or pair 3, as long as a wire is connected to the pin it needs to use.
The TIA/ EIA standard specifies eight-position, eight-contact jacks and plugs and four-pair cables, fully terminated, to facilitate this universality. The T568B wiring configuration was at one time the most commonly used scheme, especially for commercial installations.
The TIA/EIA adopted the T568B wiring scheme from the AT&T 258A wiring scheme.
The T568A scheme is well suited to upgrades and new installations in residences because the wire-termination pattern for pairs 1 and 2 is the same as for USOC. Unless a waiver is granted, the U.S. government requires all government cabling installations to use the T568A wiring pattern.
The current recommendation according to the standard is for all new installations to be wired with the T568A scheme.
Keep the following points in mind when terminating UTP connectors. When connecting to jacks and plugs, do not untwist UTP more than 0.5″ for Category 5e or more than 0.375″ for Category 6.
Always use connectors, wall plates, and patch panels that are compatible (same rating or higher) with the grade of cable used. To “future-proof” your installation, terminate all four pairs, even if the application requires only two of the pairs.
Remember that the T568A wiring scheme is compatible with USOC wiring schemes that use pairs 1 and 2. When terminating ScTP cables, always terminate the drain wire on both ends of the connection.