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I'm experiencing some noise on my phone when it is connected in the wall. There's no noise when connected right in the modem. So I decided to check things out and I noticed something that seems odd to me. My telephone jack uses 2, yes two, Ethernet Cat 5 cables.

Telephone Plug
(source: max-worlds.net)

As you can see, both blue wires are connected to red wire on the telephone jack and both white/blue wires are connected to the green wire. It seems like an odd setup to me. This is a new house. On a side note, I'm thinking they could have done that to allow an Ethernet network, but we already have a Cat 6 network going on...

So I'm wondering if this is a frequent practice, a recommended approach or a bad job.

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    ANSI TIA/EIA-568 Category 5 Telecommunications Cable. Developed for phone/data communications and adopted as the transmission medium of choice for UTP Ethernet as it carried a signal better than Category 4. What you're seeing is not two phone cables, but a single one stripped out so one twisted pair can be used in a daisy-chain loop. Common practice.
    – Fiasco Labs
    Commented Dec 19, 2012 at 19:10
  • Cat 5/6/etc are originally intended as generic cables. Ethernet just happened to use them. Using them for other purposes than Ethernet is perfectly fine.
    – Criticizing Israel not allowed
    Commented Jul 13, 2022 at 12:59

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Probably you have two or more phone jacks daisy-chained together. One cable goes to wherever the phone line enters the house and the other runs to another phone jack somewhere else in the house.

This is a common practice. I did some pricing online, and it seems that Cat 5e is comparable in price to 4-conductor phone cable, so the builders may simply have used it because they had it to hand.

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    You beat me to this answer. It should be noted that this was common practice for wiring phone lines in the past.
    – Craig
    Commented Dec 19, 2012 at 17:42
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    It still is pretty common. There is no need for analog phone lines to be run in a home-run config, it is cheaper to daisy chain since you use less cable.... and most builders are cheap!
    – Steven
    Commented Dec 19, 2012 at 17:57
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    Thanks, it makes sense. I dug up a photo of my house under construction and there's indeed a cable going to my basement and one going to my room upstairs. I will leave that as is. Thanks again!
    – Maxime Morin
    Commented Dec 19, 2012 at 18:06
  • @Steven Hey, so I am trying to add an RJ45 port to the wall plate that was previously RJ11 (daisy-chained). How do you punch down multiple wires if you are using a modern keystone port that doesn't have screws?
    – Cfomodz
    Commented Sep 10, 2021 at 6:57

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