Can you get two pairs of 10/100 connections out of a four-pair Cat 5 cable?

1545 pts.
Tags:
Cabling
CAT 5
IEEE
IEEE 802 standard
Network hardware
Networking Equipment
On a Cat 5 cable with four pairs I know that you can get 10/100 TX out of one pair which is the IEEE 802 standard. But can you also utilize the other two pairs for an additional 10/100 TX network drop? Will this work? Where is it stated that you cannot do this if it does work and someone is saying it's not the IEEE standard?

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It requires two pair for 100 TX. You can technically “split pairs;” however, the standards tell you not to split them behind the faceplate and that all four pairs should be terminated into a four-position jack. (This will not be an IEEE standard, but rather TIA or ISO — whichever you follow). You can buy a splitter that is in front of the faceplate that will allow you two 10/100 connections.

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  • petkoa
    Hi, I have tried this and it works. However, if you plan to move to gigabit, you'll need all 4 pairs... BR, Petko
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  • Coss
    Yes it does work, but I would only use it in an extreme case, and not for a permanent install. You can get cross talk on it. If you are doing it as part of a wiring job for a client, I would not do it. Coss
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  • Chippy088
    Also, it will not work if the device is to work in full duplex mode. all 4 pairs are needed for this to work. I am wondering why this question was posed, and what devices it is intended for? For this to work, the end of the cable will have to have a longer length of pairs exposed at each end to connect the 4 devices. 2 devices connected into 1 (router/switch etc) will not work. I agree with the other warnings, and would not do it, whatever the reason.
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  • petkoa
    My, my, two-years-old question is revamped! Some comments: It's intended for 100Mb ethernet, on existing cabling where neither additional cabling nor wireless is an option. Pro: Price of new cabling in an old office. Security of wired vs. wireless link. Poor quality of wireless signal in an old, thick-walled, thick-floored, weird geometry building. Full-duplex 10/100Mb works OK - it needs only 2 pairs. There is no significant cross-talk - at least not detrimental for 100Mb link (as long the pairs are really twisted :o)). Splitting could be made on patch panels and double wall jacks - no cuts, no loose ends. If no pairs are wrongly wired at the patch panel/wall jack, no problems with the switches. Contra: It doesn't work for 1Gb - this one needs all 4 pairs; since nowadays every MB comes with Gb ethernet on it, soon customers would expect working at this speed with the files on fileserver: no way on a split cabling. So warn them good, if they insist on splitting. PS: I really used it at a customer site and they have no complains for already full 4 years.
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