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CAT6 versus CAT5

  1. Jul 24, 2008 #1
    Does anyone know what the number of twists per inch is for CAT5 and CAT6 cable?
     
  2. jcsd
  3. Jul 24, 2008 #2

    berkeman

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  4. Jul 24, 2008 #3

    berkeman

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    BTW, remember that when there are multiple twisted pairs in the same sheath, they all use different lay lengths (distance per twist). This is to cut down magnetic cross-talk between the pairs. So what you are asking for is what is the allowed range of lay lengths for cat-5 and cat-6 cable...
     
  5. Jul 24, 2008 #4

    berkeman

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    Man, this is turning out to be hard! The vendor cable specs all talk about the multiple pairs having different lay lengths, but don't say what they are. I even did a directed google search on the EIA spec, but they are copyrighted documents (like Cat-6 is TIA/EIA 568B.2-1), which you have to purchase.

    I think an engineer that I work with purchased either the Cat-5 or -6 spec last year. He's gone for the day, but I'll check with him tomorrow morning. In the mean time, you can estimate it from a picture....

    http://www.germes-online.com/direct...at_5e__and_Cat_6_Cable__Solid___Stranded_.jpg


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  6. Jul 25, 2008 #5
    Hi berkeman...

    Thanks for the replies...sorry I didnt get a chance to check back until this morning...

    Thats exactly what I found yesterday before I posted...I thought maybe there was some document with the information that I was just overlooking...


    Cool....thanks.

    I could swear I thought it was close to 3 twists per inch...but Im not sure....
     
  7. Jul 25, 2008 #6

    berkeman

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    Okay, a little progress.

    From TIA-EIA-568-B.2 TIA Final.pdf, section 4.3.3.3 on color codes for 100 Ohm Cat-5/6 twisted pair, they say this:

    "For cables with tightly twisted-pairs (all pairs less than 38mm [1.5 in.] per twist), the mate conductor may serve as the marking for the white conductor."

    In section 4.3.3.2, "Pair Assembly", all they say is the "pair twist lengths shall be chosen to ensure compliance with the transmission requirements of this standard."

    In section 6.3 on Mechanical Cross-Connect Jumpers, where it talks about connecting cables together with jumpers, it says, "Twisted-pair conductor lay lengths for 24AWG or larger stranded conductors shall not exceed 15mm (0.6 in)."

    So I wasn't able to find an explicit specification on the range of allowed lay lengths, but those numbers do give an upper bound of 1.5 inches per twist (which is pretty loose -- most cables seem more tightly twisted than that).

    Hope that helps some. What is your application where you need to figure this out?
     
  8. Jul 28, 2008 #7
    Hey thanks for the information berkeman! I appreciate it...

    We are making some very short ethernet cable pairs for a government application. I recommended that we just go with 3 twists per inch...I believe this will be sufficient to reduce any induced voltages/currents....
     
  9. Jul 28, 2008 #8

    berkeman

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    If it's just one pair, that sounds reasonable. Be sure to meet the Zo requirement. If it's a couple of pairs, do the different-lay-lengths trick to cut down on cross-talk.
     
  10. Jul 29, 2008 #9
    I know what you mean....we had a discussion about this actually.

    I'm going to ask the cable techs if they can do that, but I'm not sure if they will...

    They might just look at the drawings and do all of them the same :(

    There are probably 1-2 dozen pairs so hopefully I can convince them to do a few different twists per inch....
     
  11. Jul 29, 2008 #10

    berkeman

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    If they have the same lay length in the same sheath, you most likely will not be able to meet NEXT specs, and the cable could be rejected. Tell that to the techs!
     
  12. Jul 31, 2008 #11
    I will....

    I think I'm gonna suggest the wrap them by hand and just use 1-3 twists per inch instead of 3 for each. I'll explain why and tell them to just do each one slightly differently....hopefully that will reduce any potential NEXT.
     
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