CAT5 vs CAT6 Cable: Twists Per Inch Comparison

[Firefox123]

Does anyone know what the number of twists per inch is for CAT5 and CAT6 cable?

 

[berkeman]

You should be able to find the datasheets at Belden's website:
http://www.belden.com

Sorry, I don't have much time at the moment to look for them.

But, I did find some interesting papers comparing category 5 and 6 cables:
http://www.belden.com/pdfs/Techpprs/Cat6vsCat5eforVoIPDiscussionPaper.pdf
http://www.belden.com/pdfs/techpprs/What_is_Category_6_Q&A.pdf

 

[berkeman]

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...

 

[berkeman]

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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[Firefox123]

Hi berkeman...

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

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.

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

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...

Cool...thanks.

I could swear I thought it was close to 3 twists per inch...but I am not sure...

 

[berkeman]

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?

 

[Firefox123]

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?

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...

 

[berkeman]

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...

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.

 

[Firefox123]

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.

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...

 

[berkeman]

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...

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!

 

[Firefox123]

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!

I will...

I think I'm going to 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.