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Use of "spare" wires in CAt5e cabling?

Last response: in Networking
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April 14, 2006 10:54:40 AM

Please bear with me in this question as Im no a network specialist!

I have a problem with a house Im building at the moment. The builders have omitted the telephone cabling and its going to be tricky to fit now that the internal plasterboard is complete. They have correctly installed CAT5e network cable throughout though, and my understanding was that only 2 of the 4 twisted pairs are actually utilised for 100BaseT network.

I wondered if it was possible to breakout the 2 spare twisted pair wires and use them for telephone distribution. I have a few specific queries with this :-

1) Are these wires actually spare or do all 4 twisted pairs have to be connected
2) Are there any existing or emerging networking technologies which need them
3) If we get as far as this, could interference be an issue (Im UK based if the type of telephone is a regional issue)

Any help much appreciated (before we start busting down walls!)
April 18, 2006 11:37:04 PM

100BaseT uses 2 pairs, 1000BaseT (gigabit) uses all 4 pairs. If you want to be able to go to gigabit you will need all of the wires. Otherwise I see no reason why you couldn't send data and phone through the same cable.
Phone lines should be low enough voltage to not pose much of an interference problem.
April 19, 2006 9:50:48 AM

Thanks for your help. I think to future proof my system I'll insist on additional wires being pulled.
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April 19, 2006 11:02:52 AM

I am not so sure about that. A couple of time when rewiring the tel network at home I’ve got a nasty shock (Happens when someone calls). Don’t really know if that can interfere with the network signals though……………
April 20, 2006 12:17:52 PM

Yes you can, I have done it in my house. However, it appears that if you ever go 1000BaseT you might be in trouble with the phone in that room.
April 25, 2006 3:01:27 AM

Yes it can be done as posted but also as posted you will have limited yourself when futur proofing your speeds and also as posted the line surges to well over 110 volts but that is not the issue. There, without being redundant is no issue except for the fact of current. When the line surges during ringing the line also surges to about 1 ma (milli-amp). Just make sure you are using a shielded pair of cables (I don't think they sell anything but that now) and that everything they pulled through the house has not bad spots in it. You might experience line noise when the phone rings but nothing that should knock your network connection off and another issue is your home insurance. They will not let BellSouth, here in Alabama, do what you suggest or shall I say my insurance company because I tried to get them to do it. They explained to me in some Southern slang that the insurance would not cover it under fire regulations or somethign to that effect.

Good Luck.

Ranger
April 27, 2006 9:55:31 PM

Obviously, as people have said, it does not help with future-proofing. Shielded cables make no difference to the inteference running telephones down the cable would create, as the shield is on the outside of the pairs, and are not shielded individually, but as a group af 4 pairs, so that is wasting money.

I am a network engineer/telecomms engineer, and would never run telephone down a cat5 cable which is being ran as a data link too. For one thing you will have a nightmare trying to terminate one cable into 2 jacks, and 2 patch panel ports.

There will be significant intererence on network and telephone line, and it is certainly not in any standard from the IEEE/TIA.

You could however, buy an IP phone, and unplug your computer, plug in your phone, and repatch when you want to use your phone, then reverse this when you want to use the computer, this will be akward I know, but the other alternative is, get more cables ran in.

Hope this has helped. :D 
!