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What's the Difference Between T568A and T568B?



When it comes to wiring RJ45 data jacks and plugs, ANSI, TIA and EIA agree on two wiring standards: T568A and T568B. While these standards are very similar and can oftentimes be chosen according to nothing more than the installer’s preference, there are a few significant differences between the two, and it’s very important to know about these before you begin to build – or expand – your network.


How are T568A and T568B similar?
The main similarity between T568A and T568B is that they both provide wiring schemes for terminating twisted-pair copper network cable (CAT cables) to 8-position RJ45 jacks and connectors. “8 position” refers to the fact that RJ45 data transmission requires 8 conductors, which are provided by the 4 twisted wire pairs found in the copper-based network cable we just mentioned. The pairs in this type of cable are based on four colors (blue, orange, green and brown), with each of pair consisting of solid-colored wire twisted together with another wire that’s of the same color, but striped with white. When untwisted, the 4 pairs result in 8 individual wires: one for each pin of the jack or plug.


What do the T568A and T568B wiring schemes look like?

diagram of the T-568B standard
diagram of T-568A standard


What makes them different?
If you look closely at the two wiring diagrams shown above, you’ll see that the only difference (to the eye, at least) between T568A and T568B is that the pin positions for the green and orange pairs have been switched. But aside from the color reversals, there are a couple of compatibility factors that can affect your choice of an RJ45 wiring scheme.

Even though backward compatible with both one-pair and two-pair USOC wiring schemes, T568A has been largely superseded by the more up-to-date T568B. T568B and has become – overall – the most widely chosen wiring schematic because it matches AT&T’s old 258A color code, but at the same time accommodates for current and future needs. In addition, T568B offers backward compatibility with USOC, though for only one pair.


Can T568A and T568B be combined or interchanged? How do I know which one to use?
As a general rule, T568A and T568B should not be combined or interchanged. Keeping in mind that T568B is the preferred format for new networks in the United States, you’re (technically) free to choose either wiring scheme for cases in which a new network is being built from the ground up. But when an existing network infrastructure is being expanded upon, it’s vital that you find out (through either records or cable testing) which wiring schematic was originally used, and continue on within that standard.

Why is it so important that cabling updates and additions be made in accordance with the network’s original wiring standard? Continuity. It’s simple, really… if the wires don’t match up color-to-color and stripe-to-stripe when plugs and jacks are connected, data signals just won’t transfer.

There are rare instances when T568A-wired components need to be connected to T568B-wired components, and in these cases, a crossover cable (a patch cord that has an A-configured plug at one end, and a B-configured plug at the other) is used to smoothly transition between standards without compromising data.


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(based on 5 reviews)

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        (3 of 5 customers found this review helpful)


        T568B Preferred?

        By The Professor

        from Tampa, FL

        Looking in the latest TIA-568C.1 it stats that T568B is "optional" not prefered. If you want true backward compatibility with the old USOC wiring scheme then T568A is the wiring scheme "preferred".

        If you look in all of the TIA FIPS standards, T568A is the only wiring scheme mentioned.
        If you look in the TIA-570 Residential standard. T568A is the only wiring scheme mentioned.
        Even AT&T engineers are specing T568A these days.

        As far as which wiring scheme is more "popular", as a Tech and instructor who has traveled to almost all 50 states. I can tell you that the "popular" wiring scheme is "regional".

        (8 of 10 customers found this review helpful)



        By Bob M.

        from Dallas, TX

        About Me Power User



          • Confusing

          Best Uses

            It is a shame this article's Google rank is higher than the Wikipedia article, which has a much better explanation.

            If the author's use of "Continuity" refers to the wiring plan, there may be a slight amount of validity. If it refers to ELECTRICAL continuity, the author is incorrect. See the provided picture (note that cables are not connected in this manner, but this is conceptually how a signal travels thru a twisted pair network.)

            YOU CAN USE EITHER TYPE INTERCHANGEABLY, but T568B is the currently accepted standard.

            Matching up color to color and stripe to stripe DOES NOT MATTER, only that the pairs are arraigned it the order shown.

            If you are not convinced, pretend you are color blind and verify graphically or with a multimeter.

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            (4 of 6 customers found this review helpful)


            Good Explanation of Scheme and Crossover

            By wizbang_fl

            from Fort Lauderdale, FL

            About Me Enthusiast

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            • Concise
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              • Repair

              Well written information about wiring scenes and when a crossover cable is appropriate to use. Another reviewer referenced that it didn't matter how a cable is wired so long as the pairs on each end match which may or may not be true because part of the reason for the twisting is the inherent insulating properties of having different wires with other wires.

              What is true is that if not properly wired anyone who follows your work will know you didn't have a clue what you were doing.

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              (7 of 19 customers found this review helpful)


              Slightly Confused

              By Eddie the Techie

              from Astoria, OR

              About Me Power User


              • Well Explained


              • Lacking Accuracy

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                I am in training to be a computer technician and have learned a thing or three about Ethernet. As long as the wiring scheme for a single section of a network is the same, you are fine. I could wire a whole network T568A and then decide that I want the last connection to be WB,O,WO,WBl,B,G,WG,Bl and as long as both ends of that segment match, the network will still work just fine.

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                (3 of 6 customers found this review helpful)


                dont judge a book by its cover

                By electrition

                from chester nj

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                • Easy To Set Up
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                  it is a great product
                  I would ask for people to try it

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