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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Even though backward compatible with both one-pair and two-pair USOC wiring schemes, T568A has been largely superseded by the more up-to-date T568B.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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by PowerReviews

(based on 5 reviews)

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(7 of 15 customers found this review helpful)


Cabling Schemes: Continuity - Not Color

By Mart

from Altoona, PA

About Me Casual User

Verified Reviewer



    • Easily Misunderstood

    Best Uses

      "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."
      ===If the wiring is identical on the CAT cable ends then it will work, yes. And yes the RJ45 wiring scheme must be identical or the signals won't transfer.

      One can make up any color scheme provided "both ends are an identical color match". Example, having all stripes on the left and solid colors on the right in the same color order will still perform identical to either standard.

      Listed standards really don't matter, electricity & signals follow electrical pathways not color schemes.
      Any cable tester will verify if the wiring is functioning as a standard straight through cable.

      • Primary use:
      • Personal

      (4 of 6 customers found this review helpful)


      No real difference at all.

      By Jimbo

      from Australia

      About Me Enthusiast

      Verified Reviewer



          Best Uses

            There is no Transmission differences between the two cabling schemes. The North american preference for T568B is a local preference and in the wider world, T568A is the preferred option. But as long as both ends match it makes no difference to the transmission characteristics of data.

            • Primary use:
            • Business
            • Was this a gift?:
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            (17 of 24 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".

            (16 of 21 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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                • Business

                (8 of 18 customers found this review helpful)


                dont judge a book by its cover

                By electrition

                from chester nj

                About Me Power User


                • Easy To Set Up
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                • Quality Construction


                  Best Uses

                  • Replacement

                  it is a great product
                  I would ask for people to try it

                  • Primary use:
                  • Business
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                  • Yes

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