RJ45 socket, minimal untwisted, both ends the same, A or B etc -

Discussion in 'Chit-Chat' started by toastie, Nov 15, 2018.

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  1. toastie

    toastie Young grasshopper

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    -does it matter? I suspect when wiring up a RJ45 socket, you keep the untwisted wires short, consistent using the same scheme both ends, choose A or B so as not confuse any other person modifying your installation in the future. Even then some eBay sourced RJ45 modular sockets I bought don't follow the green pair/orange pair arrangement that I see on youtube.

    It's life Jim, but not as we know it.
     
  2. fenderman

    fenderman Staff Member

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    It does make a difference. You must use A or B. Use B as it has become the default. You cannot simply match the colors to each side. They are twisted to prevent crosstalk. If you didnt use A or B, you must recrimp the ends.
     
  3. toastie

    toastie Young grasshopper

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    I assumed the twisted pairs would end up adjacent to each other at the socket
     
  4. tigerwillow1

    tigerwillow1 Getting comfortable

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    Your assumption is perfectly logical, but not correct. It all started with telephone wiring. The primary telephone line was assigned to the center 2 pins of the RJ-11 connector, and a second line was assigned the outer 2 pins. This allowed a one line phone to work in a socket wired for 2 lines. (Yes, they could have kept the pairs adjacent, but they chose not to). When the 4-wire RJ-11 was expanded to the 8-wire RJ-45, the assignments for the center 4 pins were carried over from the RJ-11, and each of the two new pairs was assigned the adjacent new pins on either side of the original 4 pins.
     
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  5. toastie

    toastie Young grasshopper

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    Thanks tigerwillow1.
    I accept the history and that a standard was agreed, then along came RJ-45 A or B configuration, which you can choose which to follow. I ask this because the modular RJ-45 sockets I bought on eBay, the orange/green pairs don't match with what I see on a popular youtube clip on this subject.
     
  6. fenderman

    fenderman Staff Member

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    Doubt it...you are just misunderstanding how it's connected
     
  7. toastie

    toastie Young grasshopper

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    I could post images to show the difference between the eBay product I bought and the youtube clip, trust me.
     
  8. tigerwillow1

    tigerwillow1 Getting comfortable

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    That would be interesting to see the pictures if it's not too much hassle. The difference between "A" and "B" is that the green and orange pairs are swapped in their positions. The blue pair is always in the middle, and the brown pair is always on the end. As long as a cable is wired with a pair in the middle and on the two ends, and the last pair straddling the middle pair, it should work ok even though a nonstandard scheme would confuse the heck out of anybody looking at it.

    I'm modifying a system that has a ~150 foot cat5e run between 2 buildings. It has an attic splice using red scotchloks. If somebody asked my advice on doing this I'd say the cable wouldn't work. Yet it has been working reliably for years.
     
  9. TonyR

    TonyR IPCT Contributor

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    • Note that the only difference between T-568A and T-568B is as @tigerwillow1 stated and shown below.
    • And in the U.S., most folks use B on both ends as @fenderman stated.
    • For the record, crossover cables (A on one end, B on the other) are no longer needed for some time now, since about late '98 with the coming of Auto MDI-X. Auto MDI-X ports allow a PC to communicate directly with an IP camera; no crossover cable, no switch or hub needed.
    ieb4637_2.jpg
     
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  10. tangent

    tangent IPCT Contributor

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    RJ-45 punch down blocks and patch panels don't necessarily have colors labeled in the same order as the T-568A and T-568B standards. Most of these labels also have numbers for each position and if you look at the label in sequential order it should match T-568A and T-568B. Most punch down blocks give both color codes.

    Basically what I'm saying is there isn't a standard for how the circuit board is laid out between the jack and the block. What matters is that the block is properly labeled such that the rj-45 jack is connected correctly to the right wires. As an example, look at the images of the jacks below.

    [​IMG]
    [​IMG]
     
    Last edited: Nov 16, 2018
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  11. TonyR

    TonyR IPCT Contributor

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    Very true. I like the ones like in your first example with the deep channels for the punchdown tool. But flip the jack over, get under a dark desk on your knees, I need some help so I don't want to even see the "A' side and I black it out with a Sharpie, like below.

    That's because I terminate mostly male RJ-45's and have the color code memorized directionally and based on the locking tab orientation; I don't do many female jacks and have to pay attention to where that specific manufacturer wants that color. If I think long and hard I can associate the pin #1 with the color but, again, I want it quick and correct when I'm doing a wall jack under not-the-best-conditions for an old fart with 2 herniated disks and dim eyeballs. :facepalm:

    iu.jpg
    Which prompts this question: why the heck are so many people that pull in CAT cable (but are NOT the ones terminating it) so @#$%^ stingy with a few feet of slack? Are they going to increase their profit margin by about $.15 by keeping that 3 feet on the @#$% roll? C'mon, man....I think it's because they aren't the ones that are going to be terminating it. I always leave enough to make my job (or someone else's) easier.

    I learned long ago (and the hard way) you can make a cable shorter easily and quickly but NOT SO when it comes to making it longer.:headbang:
     
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  12. looney2ns

    looney2ns IPCT Contributor

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    I like the Levitons.
    [​IMG]


    I have also been known to sport one of these in situations such as @TonyR describes.
    [​IMG]
     
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