Hack Your House: Run Both Ethernet and Phone Over Existing Cat-5 Cable




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The new fad when building a house is to run Cat-5 cable to every wall jack. These jacks can then be used for either ethernet or phone. When we got our new house built, we chose to get four of these jacks, and we intended to use them for phone service. Unfortunately, the wifi is a bit flaky in places (even with two access points.) This got annoying up until the point where three of the four wall jacks were being used for ethernet, leaving just one for phone. This was a problem.

The solution is to run both ethernet and phone over the same existing cat-5 cable. Every wall jack becomes two jacks, one RJ-11 for phone and one RJ-45 for ethernet. This neat hack could save you a lot of money, as you only have to buy new wall plates and jacks rather than wall plates, jacks, and hundreds of feet of wire.

See how this works in the next step.

Disclaimer: I'm not sure if this is legal. The telephone company won't be pleased if you short your telephone wires together. However, if you do everything right, they won't care. Don't blame me if you shock yourself (unlikely), damage Ethernet devices (also unlikely), damage phones (not as unlikely), damage your house wiring (not too unlikely), or damage your fingers with knives (rather likely).

Step 1: Theory

This is made possible because of the wasteful (some may say "spare") wires in cat-5 cable.

Cat 5 cable and RJ-45 jacks have eight wires.
Ethernet uses two pairs (four wires), one for send and one for receive.
Telephones use two wires.

Therefore, you can run both ethernet and telephone over the same wire, and still have two wires left over.

In fact, you could run two Ethernet jacks from a single cat-5 cable, or four telephone lines (though I don't know why you would run multiple phone lines.)

This Instructable will focus on changing wall plates from one RJ-45 (Ethernet) jack into one RJ-45 and one RJ-11 (phone) jack.

Note that I have not done extensive testing with cross-talk between phone and ethernet, though I have seen no degradation in the quality of either when both are in use.

Also note that this procedure will not work with PoE (Power over Ethernet) devices. Nothing bad will happen, it just won't transmit power. See step 13 for a possibly unsafe way to keep your PoE and add phone service. Also, it will not work with gigabit ethernet-- gigabit ethernet uses all four pairs. It will work fine at 10/100 Mbps which is sufficient for most people.

Step 2: Parts

1. A house wired with Cat 5 cable and RJ-45 jacks
  • To see if you are eligible, see check the three things shown in the picture. Your system also needs to converge at a central box where you can place an Ethernet switch or router.

2. An existing modular jack system.
  • Our house used Leviton QuickPort plates and jacks from Home Depot. This is not strictly necessary, but if you don't you will have to spend extra money on more jacks. This Instructable will assume you are augmenting your existing modular jack system.

3. Wall plates with an additional hole, one for each plate to be replaced
  • In my house, one two-port plate could be reused, but a three-port plate and many more two-port plates had to be purchased.

4. RJ-11 jacks, one for each plate to be replaced
  • If your house did not have modular RJ-45 jacks you will need to purchase those too.

5. Half of a 6-ft or longer phone cord, one cord per two jacks.

5. Either a multitool, or a screwdriver, pliers, wire cutters, wire strippers, and knife (razor helps.)

6. Soldering iron and decent soldering skills. "Helping hands" suggested.

In total, to rewire five jacks, I spent about $28. This cost does not go up linearly, as you can purchase items in bulk.

Step 3: Disassemble Existing Plate

Unscrew your plate from the wall. Pop out the RJ-45 port, and pull the wire out from the wall as far as you can.

Step 4: Remove a Pair

Ethernet does not use the brown or blue pair in Cat-5. I chose to use the brown pair. You may use either.
  • Be warned that if you use the blue pair, your RJ-45 jack will no longer be able to carry phone service. However, you will hopefully have a separate phone jack soon, so this will not be a problem in the long run.

Using a knife or small screwdriver, break both of the brown wires as close to the jack as possible. Avoid all the other wires. If you break any of the other wires, you may have to redo the entire jack.

Using a knife, cut out a small section of the cable jacket about three inches from the jack.

Using a knife, screwdriver, or pliers, lift up the brown twisted pair and remove them so they stick out this hole.
  • I do not recommend using a knife to do this, as you may damage other wires.

Step 5: Crimp Phone Jack and Reassemble

At this point, you need to establish a standard way of wiring the phone jack. It is a completely arbitrary choice.

Here is how I did it:
Brown Striped Cat 5 -> Red Telephone
Brown Solid Cat 5 -> Green Telephone

Follow the instructions on your phone jack to crimp the brown pair into the red and green wire slots on the jack. This must be done in the same order on every connection (see above.) Use a knife to trim the extra.

Once this is done, reassemble the jacks using a faceplate with one additional hole.

This end of the connection is now done.

Step 6: Locate Head-end of Cable

You will need to find the origin of the chosen cable. Mine were conveniently labeled and came with a paper showing where each one goes. If this is not the case for you, you may have to trace them using a cable tracer. You can borrow this from your local networking guru.

My cables were terminated with RJ-45 plugs. If you have jacks or loose wires, your job is easier.

Once you have located the other end of your cable, remove it from the panel. If possible, bring it to a flat surface you can work on.

Step 7: Remove a Pair Again

Using a knife, remove a small section of cable jacket as close to the RJ-45 plug as possible.
  • Now is not the time to damage wires-- if you do, you will have to crimp on a new RJ-45 plug, which means more money for parts and a second trip to your local networking guru for a crimper. However, if this happens, you can simply not crimp in the brown pair and not have to remove it afterwards. It's still not worth it to re-crimp the ends.

Using side cutters, clip the brown pair close to the plug.

Remove a small section of cable jacket a few inches from the RJ-45 plug, as you did in step 4.

Again, using a small screwdriver, pliers, or a knife if necessary, extract the brown pair so it sticks out from the cable two or three inches from the plug.

Step 8: Mutilate Phone Cable

Take a phone cable and cut it in half. You only need half of a cable per jack.

Inside you should find two wires surrounded by a jacket, similar to Cat 5 cable. Carefully cut and peel back the jacket, leaving an inch or two of wire sticking out. Trim the excess jacket.

Step 9: Select Proper Wires

You need to figure out which wire in the phone cable is red and which is green. Mine were both physically colored black. To figure this out, you can find a phone cable that does have colored wires and use it for reference (you can see the colors sticking into the clear jacks.) You can also search online or use the picture provided here.

Step 10: Solder Phone and Cat 5 Together

Strip and solder the red phone wire to the striped brown Cat 5 wire, and the green phone wire to the sold brown Cat 5 wire.
  • I found it helpful to only strip the two wires I was going to solder together, to avoid mix-ups.

Tape the two wires separately to avoid shorting them together. Neither you nor the phone company would appreciate this. Tape the entire custom connection to the Cat 5 cable so that it appears nice and neat.

Step 11: Test

Plug the RJ-45 plug into a router or switch, and your computer into the RJ-45 jack. Test this connection.

Plug the RJ-11 plug (the one on ex-telephone cord) into the phone junction panel.

Plug a phone into the RJ-11 jack. Listen for a dial tone.

Step 12: Troubleshooting

If both connections work, congratulations! You can get pretty fast at the process and do each jack in half an hour or less.

If the ethernet connection does not work, you need to find the problem in the wires. You may have accidentally cut an important wire trying to remove the brown pair from the jack. You may have also done this where you tried to remove the cable jacket.

In most cases, the only good way to fix this is to re-crimp the terminator onto the cable. Other fixes such as soldering will greatly degrade the quality of your connection. Remember that twisted-pairs in an ethernet cable can only be untwisted for half an inch on each end of the cable, or else crosstalk will occur.

If the phone connection has problems, first examine the physical wires. Most likely the bending or cutting of these wires has caused a break in them. If you find a break, it is acceptable to solder it to fix it-- phone is not as high-quality as ethernet. A multimeter may be helpful here.

Afterwards, check that your wires are attached to the proper place on the jack. One wire should go to the red terminal, and one to the green terminal. Do not confuse the green terminal with the solid green Cat 5 wire.

Finally, check that your wires are the same on both ends-- that is, brown striped to red, solid to green. Most likely it is a different problem, as long as you were diligent enough to double-check all the orientations.

Step 13: A Few Words on PoE

Power over Ethernet is a technology that allows ethernet devices such as access points to operate without the need for wall power. It is not used widely except in businesses.

It sends power by placing a potential between both brown wires (-) and both blue wires (+). Since you disconnect one of these pairs using this method, PoE will simply stop working (it is not dangerous to use PoE devices, the wires are simply disconnected.)

If you desperately need to use a low-power PoE device, you may get around this by only using one wire from each pair for phone. One example of this would be the striped brown wire and the striped blue wire. Then, the solid brown wire and solid blue wire would continue to work for PoE. However, this halves the maximum current that the cable can handle and may present a fire hazard when using large power-hungry devices. I do not recommend this, but it is a possibility.



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147 Discussions


2 months ago

Also please note that if you do this POE (Power over Ethernet) is NOT supported


11 months ago

Does this work in the UK as well or just USA?


11 months ago

Does this work in the UK as well for phones or just USA?


3 years ago

what else you can do with cat5 free wires
1. phone+ethernet(100MB)
2.ethernet 1G
3. poe(power over ethernet) active/passive
4. AC(for advanced users)
5. dorbell
6. etc

on first photo phone and ethernet via cat5
on second photo 10 ethernet,2phone lines,1 1gb, and 220vAC (for power routers, switch,2home server)


2 replies

Reply 1 year ago

Gigabit requires Cat5e. Cat5 (100MHz) doesn't have the bandwidth to sustain the gigabit signaling rate (135MHz).


Reply 1 year ago

gigabit works fine on "china" aluminium cables.... bat with lost of cable distance.
also i nptised that 1g works on uncat cables (diametr of wire from .32 till .52mm)

frequency 135 is ideal conditions in datasheet.


7 years ago on Introduction

Rather than hack apart your wires in the wall, you can buy or build what's known as a "splitter." You put one on each end of the wire. They're easily available to split the cable into two ethernet channels, or four phone channels. Making a custom one is as easy as doing what you did here with a short piece of cable and putting a plug on the end of it. Keep the wires as close to their original configuration as possible to minimise the amount of interference you pick up. (Read don't untwist the wires any more than absolutely necessary, and have them fork off from each other at the last possible moment.)

The advantage to doing it this way is that it's not permanent so you can reconfigure your panel any which way you want in the future.

I can probably be convinced to post an instructable about making splitters if anybody's interested.

3 replies

Reply 3 years ago

is it possible with Gigabit cabling? there are RJ45+RJ45 and RJ45+RJ11 splitters available in market so suitable cable RJ45 to RJ11 also.


1 year ago

I'm also going to get exceedingly pedantic here.

When you see the letters "RJ" in front of a number, like "RJ11" and "RJ45", that does NOT refer to the actual connector. RJ stands for "Registered Jack" and is defined in the Uniform Service Ordering Code, and refers to a specific type of circuit provisioning - so when the phone company dispatched a tech to the field to install a circuit, they would specify an RJ code, which told the tech a few things:
• What type of connector was required (typically a "modular connector" that we're all familiar with)
• The pinout of that connector (and how many contacts the modular connector needed)
• What type of circuit it was

RJ11 defines a single telephone line on the two center pins of a 6-position/2-contact (6P2C) modular jack. An analog telephone requires RJ11 configuration, and as such has a 6P2C modular plug on the end of its cord.

RJ14 is a similar spec for either a dual analog line (line 1 on the middle 2 pins, line 2 on the outer 2 pins), this time on a 6P4C jack/plug. This was also used for digital PBX handsets that required separate pairs for power and signal.

RJ25 a three-pair phone specification on a 6P6C jack/plug.

all the 6P connectors are interchangeable.

The handset connection on most phones is a 4P4C plug but is not used by any RJ definition.

RJ45 was a single-pair data circuit specification on an 8P8C connector with the data on the center two pins, and a resistor between pins 7 and 8 (where the brown pair goes on TIA/EIA 568).

There are about a dozen other RJ specs that use the 8P8C modular connector (RJ31X being very common for alarm panel connections (in fact, your connection block above shows that as "line seizure). Since 8P8C with TIA-568A/B was also commonly used for Ethernet, the connector itself over time began to be referred to (incorrectly) as RJ45.

TIA-568A is wired to be compatible with RJ11 and RJ14 (as shown above, you can put a 6P modular connector in an 8P modular jack).

From a terminology standpoint, RJXX is equivalent to TIA-568A/B in that it defines the specific XPXC wiring scheme rather than the connector itself (although by defining the wiring scheme, it specifies a particular connector)


3 years ago

How to Know whether it is Gigabit or ordinary cabling? cannot we use RJ45 +RJ11 female adopters at both wall points to run phone off course with filter.

2 replies

Reply 1 year ago

Gigabit is determined by the equipment on the end, but gigabit requires all four pairs.


Tip 1 year ago on Introduction

It's not really an issue of being *legal* - the phone company's responsibility ends at their Network Interface Device (NID), commonly known as a "Demarc" (short for "Demarcation point"), which is the gray box on the side of your house. Anything on the customer side is not their problem. They will, however, get annoyed if your inside wiring causes problems to their network. Not likely to happen because the telephone network is engineered to be exceedingly resilient.


1 year ago

This works for 100Mb network but if you ever plan to or are running a Gigabit 1000Mb network don't do this as Gigabit will use all 8 wires.


2 years ago

It's called 10Base-T wiring (Jacks) when you wire the jacks that way it's been around the Universities in Canada since the 1990's


2 years ago

Hi. This is the first time i try anything like this so i am to say the least stupid when it comes to this. So we live in an old house and out on the country. We already have a century link connecrion but wanted to add a second one. I ran a cat 6 from the phone line only connecting the blue and white and blue wire. I then connected it to a cat 6 jack. I proceeded to conect my new century link router to it and got nothing. I dont understand what im doing wrong?


6 years ago on Introduction

Hey nice post!

Lots of good information in the comments too ;)

One question: Given that the phone line is 'live' is there any problem soldering it? with an iron that is earthed?

I have 3 Irons, one is an ESD safe station, second a Goot 12watt and a el cheapo 25watt, all three have an earth pin on their wall plugs?

I guess earthing the live wire is not ideal?