Currently, my house only has one wall plate, which uses a cat5 cable that utilizes a wall plate with pre-installed wires (blue, green, white, black, red, yellow) that the cat5 wires also connect to. From it, I use a splitter to connect to my phone and modem. I am in the process of installing data ports at other locations within my house. I pulled the incoming cat5 wire from my upstairs kitchen to my basement where I have a switch. I am unclear on how to connect the incoming line to the switch and then to my modem and phone. Especially since both the phone and modem have female RJ11 ports.

  • 3
    The incoming line goes to your modem, not to your switch. Your modem converts from "phone line" to ethernet. Your switch only talks ethernet.
    – brhans
    Commented Sep 16, 2020 at 1:31
  • 4
    The wire you're describing has 6 wires, and sounds like it has all solid colors. Ethernet cable has 8 wires, 4 of which are a solid color, and the other 4 are striped with white. Essentially it sounds like the incoming wire is a phone line with 3 potential lines on it. This has nothing to do with ethernet, and can't be used for ethernet.
    – user30371
    Commented Sep 16, 2020 at 2:06
  • 1
    That's the jack (an RJ-12) being described, and the Cat5 (better called 4 pair in this context) is described as being "also connected to it" though obviously one of the 4 pairs has no place to go, and 3 of the 4 pairs are probably not connected to anything now, if they ever were.
    – Ecnerwal
    Commented Sep 16, 2020 at 2:11

1 Answer 1


Are you under the impression that you have an ethernet cable that just happens to supply phone service, but will also magically supply ethernet if you plug it into a switch?

You (appear) to have a 4 pair cable (if it's cat 5) which has probably (you're a bit unclear, but using the most likely scenario) got POTS (voice telephone, or plain old telephone service) and DSL using one pair - typically the blue pair - that's presently connected to a 3-line wall plate, but (probably) only using one line (typically the red/green pair in the center) since you mention using a splitter from that to your modem (presumably a DSL modem) and your Phone (presumably POTS.) The other 3 pairs are probably dead and doing nothing.

So, what you need wherever you relocate this cable to is to either reconnect it exactly as it was to the 3-line plate you had it terminated to before, and then to your phone (probably with a DSL filter in line there) and modem (without a DSL filter so it gets DSL), and then plug the other side of the modem into your router and your router into your switch, or if your modem is a router, plug the ethernet side of your modem/router into your switch.

The telephone side of this (POTS/DSL) has no connection to your ethernet switch.

If I'm guessing correctly, you only really need to connect the blue pair to an RJ-11 jack (Red/Green - center pair) and your splitter to your telephone and modem, or connect it to TWO RJ-11 jacks and have no splitter required. You can do that with POTS/DSL. You can't do that with Ethernet. Blue/White connects to Red, White/Blue to Green.

There are a variety of less-likely-these-days scenarios involving actually using two or three telephone lines, but they are very unlikely in the current era, and I'm having to assume a great deal, so I assume the unlikely things are not what's happening here.

Alternatively, put it back where it was, and run a cable from an Ethernet port on your Router or Modem/Router to the switch.

  • They could use the unused pairs of the RJ-45 for 100Base-TX, but that might confuse modern GigE gear that's trying to autonegotiate.... Commented Sep 16, 2020 at 2:03
  • I would strongly suggest NOT. Cable just isn't that expensive (run a whole new hunk with gig capabilities) and it makes it painful for the next poor schlub to figure out what in the name of Cthulhu you were even thinking...
    – Ecnerwal
    Commented Sep 16, 2020 at 2:07
  • @Ecnerwal you're right - cable(wire) is cheap. The hard work (time is money) is in getting it up and down walls in a way that looks undisturbed. If there's a wire in place that goes the right way, I can see the attraction of reusing that, somehow.
    – Criggie
    Commented Sep 16, 2020 at 4:36
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    @Criggie I'll let the Flying Spaghetti Monster and Cthulhu tear you apart (sharing is caring even when it's Elder Gods and Brand-Spanking New Gods sharing sacrifices, right?) if I come across this sort of abomination. Ewww.
    – Ecnerwal
    Commented Sep 16, 2020 at 15:45
  • @Ecnerwal see the image in Home Improvement Chat recently for an example of the fun inherent in running new cable. It worked though.
    – Criggie
    Commented Sep 17, 2020 at 3:34

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