I’m moving into a new house that looks to have Ethernet wired through it though it looks like it was being used for telephone?

I’m wondering if it will be usable for Internet and if so what changes I need to make/what exactly I need to do.

Also is there any way to tell if it’s all cat 5 or cat 5e?

I don’t know much about this so step by step on how to make it work for Internet would be greatly appreciated. So far my guess is that I need to pull all the wiring out of that current punch panel and add RJ45 connectors to each separate wire? At that point I just need a way to connect them to my router?

Thanks a lot!

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  • 1
    the blue cable could be LAN cable ... the rest are probably not ... check the printing on the cables
    – jsotola
    Commented Jan 31, 2021 at 11:40
  • 6
    None of that stuff looks like Cat 5, 5e, or 6. None of those cable have the suggested number-of-twists-per-inch for Cat 5 and higher cabling. It's possible its Cat3 or 4, but more likely it's just POTS (plain old telephone system).
    – SteveSh
    Commented Jan 31, 2021 at 15:22
  • 2
    Most of the wires that you can easily see the twist rate on are clearly cut from a 25-pair cable (based on the colors), and that's almost certainly POTS or Cat3 at best. Telephone folks often untwist pairs, as can be seen on some of the hanging splices. Until you read the cable jackets, you won't know.
    – Ecnerwal
    Commented Jan 31, 2021 at 16:16
  • 3
    Does this answer your question? Repurpose telephone line to ethernet Commented Jan 31, 2021 at 22:18
  • 11
    Don't assume anything, and read the wire labelling - electricians are notoriously lazy and will carry as few different types of wire as possible. So they only need one pair for a phone cable, but are carrying cat5e UTP in the hand/van? No way they'll order special wire, they'll use what's in hand and bill the customer. cat5e and cat6 are made/sold/used in such volumes that its often cheaper than 2pair phone wire anyway.
    – Criggie
    Commented Feb 1, 2021 at 0:25

6 Answers 6


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Read the jacket - I think I can see, but not make out, faint red printing on at least two of the gray cables in your picture. But there's no guarantee that all the gray cables are the same, if this system grew organically over time rather than having been all installed at once.

Even if it's CAT3, it will run ethernet (slowly by modern standards.) That will be fine for a printer that plugs into ethernet, and other uses that are not too demanding, but won't suit your faster goals - in which case you might examine how it's installed, and whether you can use the current cables to help you get new cables into the places you actually need faster connections.

Your best bet at this end would be to install a patch panel, rather than "plugs on cables" - plugs on fixed cables are iffy (they tend to fail,) while a patch panel is quite reliable, (and also easier to connect to) and helps to organize the mess.

You'll also need a switch, to get the signal from a cable leading to your router to all the other cables (or all the other cables you are actually using.)

Beware that as phone wiring, there's no guarantee that the wiring completely respects a "star" configuration (each cable here leads only one place) - some legs of the apparent star may be "daisy-chained" to more than one outlet, and that does not fly with Ethernet like it does with telephones.

  • 6
    This answer is correct. That's a phone line terminal. Phone lines don't need star network configuration, so don't expect that ethernet will just work over lines wired for phone. Also, CAT5/e/6 are just fine to run phone signals over, that's what basically everyone does these days. You can pull apart a normal Cat5 cable and get 4 phone pairs. Commented Feb 1, 2021 at 15:25
  • Depending on where you live cat3 might still outdo your internet speed (to the router) by a good margin, 10mbps is still sufficient for any casual use imho
    – Hobbamok
    Commented Feb 2, 2021 at 13:55

This was clearly being used as telephone wiring. Even if some of the cables are ethernet cables they have been cut and spliced for phone use and there may be splices hidden in the walls similar to what you see here. That's ok for phones. Even if some of them "work" for ethernet they may work slowly. You will not know, you'll just blame your ISP.

My suggestion is don't use any of this for internet. Buy good Cat6 or better cables. Don't buy the cheapest ones on Amazon, but good ones with good reviews. Run cables to a few critical spots in your home from a central location. Buy and install a mesh network with wired backhaul (so the mesh nodes all use your new cables) and buy a small switch if needed to connect it all together.

All this will cost a few hundred dollars and is worth the investment in your new home.

  • 5
    You will not know, you'll just blame your ISP. "Gosh, I get 877 Mb/sec when I plug into the router directly, but only 8 Mbit when I plug into the cable in the pink bedroom. Must be my ISPs fault" ....riiight.
    – Ecnerwal
    Commented Jan 31, 2021 at 16:09
  • 7
    @Ecnerwal although I was being slightly facetious with that comment I maintain that most people, probably including OP, either could not or would not perform such diagnostics.
    – jay613
    Commented Jan 31, 2021 at 16:41
  • 6
    "Cat6 or better" feels like future-proofing in the wrong place. 5e is all you'll ever need for home GE, Cat6 will do as well if the price difference is negligible. Buying anything like Cat7 is likely a pure waste of money. If you want to future-proof, run conduit instead of Cat7 so that you can go fiber if you ever need to. It's fairly unlikely metallic 10GE will ever become a thing in the consumer world, with more and more devices now being mobile/IoT.
    – TooTea
    Commented Feb 1, 2021 at 9:54
  • @TooTea I agree in theory but 1) I'm suggesting 2 to 5 premade patch cables of 50 to 150 feet. Cost difference is negligible. Cat5E cables on Amazon, especially cheap ones, are frequently garbage. Decent Cat6 cable is an extra $6. 2) Installing conduit for future fiber is ambitious given OP circumstances (just moved in) and knowledge, I think running a few premade patch cords and setting up a Mesh network should be his first step. And 3) Given improvement in Wifi and 5G, what future application do you envision for in-home fiber? I'd like to know!
    – jay613
    Commented Feb 1, 2021 at 14:10
  • 2
    @jay613 I don't see any applications at the moment and I can't see into the future. But that's exactly my point. I don't think OP will ever need 10GE, but I think it's way more unlikely that they will need one particular kind of metallic 10GE (or 5GE, …) that requires Cat6a/7/+ twisted pair. Anyone who really wants to invest into future-proofing their home network should do it the conduit way, precisely because it's hard to pick a particular future networking technology at this point.
    – TooTea
    Commented Feb 1, 2021 at 14:24

The grey stuff is often non-twisted pair, or unshielded twisted pair. As others have said, read the label.

The blue stuff could be cat 3 or cat 5, but unless you have access to both ends, it's a crap shoot whether it has a continuous run. You may be able to figure some out by temporarily unhooking wires, and seeing where you have dial tones.

You have some decisions to make:

  • Do you need wired LAN throughout your house. If you do lots of internet file sharing, or run a home server, then the answer is yes, at least between the server and your internet access device. If you stream TV at anything above default resolution you will want a wired link between the internet access point and the TV device.

  • You may also want it if you have several people who want to use high bandwidth applications at the same time. SOHO operations that use cloud SaaS may need this.

  • Wifi works pretty well. But the closer you are to the wifi access point, the faster it is. You may want LAN between your internet access point and your wifi units at various places in the house.

In its simplest form all your house wires come to a patch panel. There a short patch cable runs from the panel to your switch.

Wire for stuffing in walls isn't stranded. This gives it less electrical resistance, but also makes it stiffer. It has less tolerance for being bent. Patch cables are either stranded, or are made from softer copper.

  • 3
    "Wifi works pretty well." - that really depends on where you live. If your walls act as Faraday cage (many places in Europe) or you live in dense city (so there is lot of interference) you might run into problems. Commented Feb 2, 2021 at 3:36
  • @MaciejPiechotka exactly my thought lol. In my parents house we didn't have wifi through a single wall with the sole exception of those my parents had put in during renovations. We ended up wiring almost the entire house because it was just the worst
    – Hobbamok
    Commented Feb 2, 2021 at 13:57

The wiring workmanship shown here, no matter what the cable type is, cannot be relied on to yield satisfactory ethernet operation. The way twisted pairs are untwisted for several inches, with the individual wires crossing other wiring in an uncontrolled fashion... stubs of old parallel connections just left dangling... if it works, it is still likely to cause and/or be sensitive to RF interference. The reason the wires are twisted in a twisted pair cable is NOT mechanical and NOT a stylistic or manufacturing choice.

If the actual intent is running a DSL line to a router, it could work - unlike ethernet, DSL is DESIGNED to work around imperfectly done wiring. However, even DSL cannot always deal with a so called bridge-tap situation that might be present here (multiple lines wired as parallel circuits, even if there is nothing connected at the end of the circuit - all these communications technologies work with RF electricity; the concept that a circuit with no load connected does not matter is NOT true with RF).

  • 2
    Yes, it's rather obviously currently telephone wiring, so there's no reason to expect it to "yield satisfactory ethernet operation" in it's current form. That's also not the question.
    – Ecnerwal
    Commented Feb 1, 2021 at 2:00
  • >cannot be relied on to yield satisfactory ethernet operation. | yeah, but just redoing the plugs at both ends is a twenty minute task costing a few bucks VS redoing the cabeling which will run you days and a good bit of cash
    – Hobbamok
    Commented Feb 2, 2021 at 13:58
  • @Hobbamok Putting plugs on the ends of crap wires only wastes plugs and "20 minutes". (Chances are anyone asking this question to begin with has zero to very little experience putting ends on Ethernet cable, so 20 minutes is pretty generous estimate.) Even by some freak chance it works, it won't work well or reliably. It's better to cut the crap out and do it correctly...Both to ensure future compatibility and also to avoid fighting with it.
    – gnicko
    Commented Feb 5, 2021 at 19:49

Technically, yes. When my roommate and I got our first cable modem some 20 years ago, a friend of his ran Cat3 into my room (he had lots of the stuff) and wired it up and it worked well enough for the 2 years we lived there.

I say technically because he simply provided the minimum Ethernet needs. Ethernet uses only 4 wires to work on the data end, so his friend crimped RJ45 jacks on using only pins 1, 2, 3, and 6. There's two major caveats here

  1. Cat3 isn't designed for shielding at all. Shielding is somewhat important to Ethernet. In my case, the wire was stuffed under the baseboard down a hallway (where there's virtually no interference). It was also a 10MB network, not the 1000MB you commonly find today.
  2. You can't run any Power over Ethernet (PoE), since pins 4, 5, 7, and 8 are all missing.

So you can try and it might be passable for a home network, but it isn't the right tool for the job and it may not be forward compatible.

  • 5
    Sheilding is not important to ethernet. I run thousands of feet of Cat5e unsheilded and it runs gigabit just fine. UTP (unsheilded twisted pair) is normal and standard. FTP or STP (foil or shielded, respectively) are abnormal. It's the twisting and how the signals are run that makes it work, mostly. Also, only 10 Mb and 100 Mb ethernet "only use 4 pins" - Gigabit uses all 8. The cables shown are 4-pair cables (and some irrelevant to this discussion 25-pair cable from its telephone job.)
    – Ecnerwal
    Commented Feb 1, 2021 at 15:18
  • Standard PoE (IEEE 802.3af) can work on the same pairs as Ethernet if the PSE (the device which provides the power) uses Mode A (usually switches rather than injectors). Mode A uses the "phantom power" technique.
    – jcaron
    Commented Feb 2, 2021 at 13:53
  • PoE is still an upcoming feature, so while it IS something to keep in mind, it would (for me) not be a reason to redo the cables. [IF the stuff OP has is indeed cat3]
    – Hobbamok
    Commented Feb 2, 2021 at 14:01
  • Shielding isn't. But clean twist geometry with as little disturbances as possible and correct wire pairing IS. The twist actually provides shielding by a very clever trick (making sure any interference on the cable is at the same time applied in reverse, thus cancelling out). Commented Feb 19, 2021 at 21:06

Is this part of a SOHO (small office, home office ) DIGITAL phone system? the 2 large cables (trunk lines I think is the term) are a clue it's attached to a KSU. Also, the connectors shown are typically used on phone lines. The smaller cables should have printed on them the type of cable. The blue ones look like cat 5, the grey ones look like cat 3 (not suitable for ethernet). Repurposing some of might be possible. But, and here's the big BUT if the phone lines are not all "home runs" and are daisy chained (common for POTS phone wiring), you can't re-use them. They're also probably cat-3, again, not suitable for ethernet.

All you can do is start tracing circuits. Get some testing equipment at go at it.

  • 1
    Thanks a lot this was helpful. Previous owner had a law firm so I think it’s safe to assume this was part of their home office. If the cables are anything less than 5e I won’t bother with it regardless as cat 5 would be slower than wifi in my case
    – Mark
    Commented Jan 31, 2021 at 12:18
  • 3
    Jacket color is not an indication of CAT level - read the (often faint) printing. Blue jacket is (usually) plenum, gray jacket is (usually) riser, and could be Cat3, Cat5, Cat5e...
    – Ecnerwal
    Commented Jan 31, 2021 at 13:32
  • 4
    @Ecnerwal Back when I used to do a lot more cabling of offices, I would get 2 or 3 different colors of the same type of cable just to make identification easier when pulling multiple cables to the same location. Commented Jan 31, 2021 at 14:51
  • @Mark what's your usecase that you're scoffing at low-latency 10mbps ?
    – Hobbamok
    Commented Feb 2, 2021 at 14:02
  • It's also important to note that much of the CAT5 that was made actually passes the specs for CAT5e without changes, other than "well that standard didn't exist when I was made so it's not printed on me" - always worth a shot to see if you get Gigabit or only 100Megabit from a particular chunk of Cat5, no "e" (as an end-user - as an installer we're often in the position of having to rip out stuff that might work fine to satisfy work-order specs/consistency.)
    – Ecnerwal
    Commented Feb 3, 2021 at 16:11

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