We are buying a new house, and I was curious about this junction box. It has several lines of coax and cat5e in it.

Each room has a blank plate, and behind it is a coax and a cat5e drop.

I was assuming that when we get Comcast,I could put the modem in this closet, with a router and switch, put ends on each Ethernet cable, and have wired connection in most rooms.

But then I looked closer and realized that 6 of the Ethernet cables are wired to 2 other Ethernet cords, using only 2 wires from each cable. Any ideas as to what this setup is?

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  • Your builder can't tell you? Seems like the kind of knowledge you're paying for.
    – isherwood
    Jul 24, 2020 at 19:28
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    But they're probably phone lines.
    – isherwood
    Jul 24, 2020 at 19:29
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    @isherwood that'd be ideal yea, but he's not been very helpful. House was built in November, and we're just buying it from a bank now. And there are no phone jacks in the house anywhere, so I don't think they are for phones. Jul 24, 2020 at 19:30
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    @brhans if it's shared phone line, then I should be able to terminate that. Tuck those 2 (presumably going to the street) off to the side, and use the other 6 lines for Ethernet Jul 24, 2020 at 20:28
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    @DickieScoob, yeah, you have basically two options: 1) leave the blue pairs as-is for phones, and use the other pairs for 100Mbps ethernet, or 2) ditch the phone lines, and use all four pairs of each cable for gigabit ethernet. Personally, I haven't used a landline in over a decade, so I'd go with option 2, but ymmv.
    – Nate S.
    Jul 24, 2020 at 21:07

1 Answer 1


Summarizing what has been said in the comments:

Having the blue pair paralleled between all the cables strongly suggests the builders intent was that they be used for phones. Cat5e cable is often used for phone wiring as it's more interference resistant than regular phone wire and the blue pair is the conventional "first pair" for phone wiring.

As for your options, there are two main ways forward.

Option 1, ditch the phone wiring cut off the builders mess and terminate the cables individually as network cables with all four pairs. This will let you run gigabit networking.

Option 2, leave the phone wiring as it is and use the green and orange pairs of each cable for Ethernet, this will limit you to 100 megabits per second.

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