RJ11 Phone to RJ45 Jack

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Cat5, Cat5e, Cat6 cable is frequently used for wiring telephone jacks. You can send up to 4 telephone lines on one 4 pair cable that terminates at a RJ45 (8P8C) jack. The problem is most phones, even multi-line phones, don't directly plug into an RJ45 jack. We'll discuss some options for connecting phones with RJ11 connectors to an RJ45 port.

Jack Configuration

Before we get into separating the phone lines, lets understand what's going on in the jack. Nobody uses the old quad (green, red, black, yellow) phone cable anymore in new wiring. It's mainly Cat3 or better cable which consists of 4 twisted pairs of wire in blue, orange, green and brown along with their white wire that has a colored stripe (white-blue, white-orange, white-green, white-brown). Since a standard telephone only needs one pair of wires per line, we can send up to 4 lines on each cable. This offers a lot of flexibility and saves time and labor running phone cables in a multi-line system. Even if you're only going to be running a single phone line, you have room for expansion.

For consistency, the ability to utilize all 4 lines and to save space in the wall jack, phone installations are typically terminated in an 8P8C (8 pin 8 conductor) jack. This is the same jack used for your ethernet cable. This is a bigger jack than you might normally expect for a phone which is typically a smaller 6P6C or similar (RJ11, RJ12, etc). 6P6C supports up to 3 lines, 6P4C 2 lines and 6P2C is a single line jack but they all use the same plug. Only difference is the number of wires in the cable.

There are three standard ways of wiring a phone jack. T568A, T568B and USOC. The difference is what colors are connected to what pins on the jack.

T568A is the preferred method for wiring telephone and ethernet jacks and the only method suggested in the residential TIA-570-B specification. Somehow T568B became popular in U.S. commercial installations but T568A is used more outside the U.S. and the Federal Government specifies T568A for their installations. To all the naysayers... See sometimes the government can do things better than the private sector. :) USOC isn't commonly used anymore but is the type of wiring scheme telephones use. 

It would make sense to wire ports following the USOC specification but by using T568A a cable can later be easily switched from voice to data or vice versa in the future. You'll notice that Line 1 and Line 2 on both T568A and USOC are identical. If you have a two line phone, you can plug it directly into a T568A wired jack and both lines will work. The smaller RJ11/12 plugs will fit directly inside an RJ45 jack. It's not preferred since you might damage the other pins but it is designed to work that way.

Unless you need to match a currently installed pinout plan, try to always use T568A. Either way, it's important to know how your jacks are actually wired.

Telephone Jack

Compare the above jacks with old style 2-line phone jacks that used to be used on walls and are still used in phones. They look like this.

The above is a standard 6P4C telephone jack that supports 2 phone lines. Line 1 is on the center pins line 2 is on the next set of outer pins. If twisted pair wiring is used the colors would be white-blue for green, blue for red, white-orange for black and orange for yellow.

If you hook up a single line phone it will only make a connection with pins 2 and 3 (line 1). With a two line phone you'll use all 4 pins.

Connecting Standard 4-Line Phone to RJ45 Jack

The Jack supports 4 lines, the phone supports 4 lines this should be easy right? Nope, not usually. The problem is that most standard 4-line phones don't have a single 4 line RJ45 jack, instead they usually have 2 6P4C (RJ11) jacks that support 2 lines each.

There are a few ways to handle this correctly but let's first talk about how not to do it. You may think that it would make life easy if you just split the pairs of cables behind the wall plate and use 2 RJ11 keystone jacks. This will theoretically work and considering it's just phone there will be minimal issues with interference having a bunch of exposed pairs but it can lead to problems. You will obviously increase the chances of having interference, the wires will be easier to damage, you're going to be taking up extra space in the wall plate and you lose the ability to easily change that port to a network port in the future. It's also prohibited in the spec.

RJ45 4-line to 2 RJ11 2-Line Adapter

There are a number of different splitters (usually named 400E) like this Suttle 400E Cat5 Splitter that plug into the RJ45 Jack and have 2 RJ11 jacks each with 2 lines. These are fairly easy to find but just make sure you're not getting a regular telephone splitter (1 RJ11 to 2 RJ11). It needs to have a male RJ45 on one side and 2 female RJ11's on the other.

Taking a close look at the wiring diagram it appears to follow T568B on the RJ45 side. You can still use it with T568A pinouts but line 2 and 3 will be swapped. If your phone jacks pinouts follow USOC this adapter won't work.

Break Out Cable

If you can't find the splitter above, you can make a breakout cable from twisted pair cable.

On one end you'll crimp an RJ45 jack following the pinout used in your wall jack. On the other you'll crimp 1 or more RJ11 jacks. If you just want to pull one line out for a single phone, pick the pair of wires for the line you want and insert them in the center pins of the RJ11. You can also do 2 2-line RJ11 plugs, 4 1-line RJ11 plugs, whatever works for you.

Break Out Box

Manufacturers of structured wiring systems also have premade break out boxes that will allow you to access the 4 lines in different ways. The Leviton 47609-4x4 4x4 Breakout Module is one example.

Since the Leviton systems are geared towards residential installations the Leviton 47609-4x4 is wired according to the T568A pinout unlike the splitter above which is T568B.

DIY RJ45 to RJ11 Break Out Box

If you can't find the break out box above or have special needs you can make your own break out box.

You can make one anyway you'd like but to give you an example let's make a a 4 port box that takes an incoming cable and splits it up to L1&2, L2&1, L3&4, L4&3 similar to the Leviton.

We'll need:
For tools we'll need:
  • Punch down tool with 110 cutting and non cutting blade
  • Modular Plug crimper
  • Screwdriver
We're going to daisy chain 2 pairs on 2 ports for Lines 1 & 2 and then do the same on 2 other ports for lines 3 &4 so we'll have 4 jacks wired like this:

With this configuration we can connect:
  • 4 separate 1-line phones to one RJ45 jack to access all 4 lines.
  • 4 2-line phones 
  • 2 2-line phones
  • or some other variations like one 4-line phone a fax machine and a single line phone.
It's snowing and I don't have any phone jacks handy so I'll be wiring it up using standard 8 wire Cat5e jacks. Same principle but I'm punching down the wires on different pins than I mention in the instructions.

Step 1: Strip cable

Strip the outer jacket of the cable fairly long (maybe 8-10") so you have plenty of wire to work with.

Step 2: L2&1 Jack

We're going to start with one of the center jacks (Lines 2 & 1) and work our way out on either side.  Untwist the orange pair of wires near the base (don't untwist the pair completely) and punch them down to pins 3 & 4 (orange and white-orange) using a non-cutting 110 blade. I'm using the plastic punch down tool that comes with the jacks. Repeat for the blue pair on pins 2 and 5 (white-blue and blue).

Step 3: L1&2 Jack

Next we'll do the Lines 1 & 2 Jack using the same blue and orange pairs except we'll punch them down on the opposite pins as before. 3 and 4 for blue and 2 and 5 for orange. This time when we punch down the wires we'll use the cutting 110 blade to trim off any excess wire.

Have a look at the jack and visualize how you want it to appear in the surface mount box. For me, I'm going to want to punch down the next jack to the right of the first one. Your jacks may be different so stop and check. Remember the pins will be on the top when mounted in the box.

Also, position the next jack far enough away so you have ample wires to position the jacks in the ports on the surface mount box. 

Step 4: L3&4 Jack

Now on the other side of the L2&1 jack we're going to add a jack for Lines 3&4 using the green and brown pairs on pins 3&4 and 2&5 respectively as shown in the previous diagram. 

Use the non-cutting blade and leave enough wire to be able to position the jack in the surface mount box.

Step 5: L4&3 Jack

The last jack is the lines 4 and 3 jack. We'll punch the green pair to pins 2&5 and the brown pair to pins 3&4 using the cutting 110 punch down blade.

Step 6: Insert Jacks In Surface Mount Box

Put the dust covers on the jacks if supplied then install the jacks into the ports on the surface mount box. Mark the surface mount box above the jack so you know it's function (L1&2, L2&1, L3&4, L4&3 or whichever configuration you chose.)

Step 7: Crimp RJ45 Connector

On the other end of the of the wire crimp on an RJ45 connector using the appropriate pinout for your wall jack. Either T568A, T568B or USOC.


  1. Thanks for the great info. I am just setting up an OOMA (VOIP device) in my study and wanted to send the phone back down the line to the distribution box for the rest of the house. This will allow me to send the phone line back down on either l3 or l4.
    Appreciate all the information which is very clear.


  2. Hi! Hope anyone could enlighten me with this.. I'm trying to make an adapter from Female RJ10 4P4C to Male Audio/Mic, but I am not sure if this is possible.. I would like to know if the cabling or pinning will still be like
    I am actually trying to use my headset with RJ10 PLUG, that's why i'm thinking of making the adapter myself since I have all the equipment needed.. Also I'm opting to use the cable of my old headset with microphone and volume control for the Audio/Mic plug, but I'm having a hard time searching if where to specifically attach the cable from RJ10 to the small-motherboard of my old headset cable. Please enlighten me folks.. Thanks ahead of time...

  3. Your color coding is wrong. If you check Wikipedia, you'll see that T568A and T568B has the brown wire as pin 8 - you have it as pin 7.
    Basically you have the brown pair incorrect on your pinout diagram. The two wires in the brown pair need to be swapped around for your diagram to be correct.

    1. Yikes! Thanks for the heads up. Fixed it.

  4. Can you show how to make an rj11 male plug on one end to an rj45 male or female plug on the other end.... i'd like to make this kind of cabling for internet connection... so that one of my internet connection will come from an adsl rj11 splitter going directly to another modem or computer. I've seen a cable adapter like this but it is'nt sold in our country. The idea behind this, is that i'd like to have my connection direct from the internet drop off box and not passing through the main modem which serves as the distributor. The problem with the modem set up is, when the modem is turned off, all internet connections are also cut off and sometimes we need to wait for the main office to open before we can use the internet because that is where the main modem is. Thanks in advance if you can show my request....

  5. Your comment about the line numbers for T568B is incorrect. T568A and T568B are ELECTRICALLY IDENTICAL. Pins 4/5 are line 1 in both T568A and T568B. Pins 3/6 are Line 2 in both T568A and T568B. That's why a 2C phone cord uses 4/5 pair, and a 2-line cord uses the next two wires on either side of 4/5, i.e., pins 3/6.

    Imagine your diagram of T568B, with the green and brown pairs physically removed. Now plug in a 4C phone cord, and you will have only Line 1 working. That is because Line 1 is pair 4/5, and Line 2 is pair 3/6, REGARDLESS of being green or orange pairs. Electrons are color blind!

    The ONLY difference between T568A and T568B is the COLORS of the pairs. They are still electrically wired identically.

  6. How do i extend and use the main wire to an existing electrical outlet so that i can run the single wire thorough the house to other electrical boxes keeping a single wire run to extend each box to another box? I need to be able to tap off each box on the single run wire. What is the best method so i do not have to have a gang of wires for my rj45 cat5 wiring?

  7. I turned the end of a cat5 cable into two RJ11 connectors (w/o w/bl bl o) and (w/br w/g g br). I got way too clever and tried to punch the other ends down to a 66 block. I am stuck and in a hole because I've done this six times throughout the home. At the 66 block, I tried 568b order (not A because that's what we always use) and got nothing really. I tried blues, oranges, greens, browns-common order and got nothing also. Can you save me here and tell me the order the wires should be on the 66 block? Again the two rj11 ends are w/o w/bl bl o and w/br w/g g br Sincerely stuck and desperate

  8. Your diagram with the cables being split into line 1 and 2 then line 3 and 4, this goes from the inside out. On the sutter connector, this isn't the case on the right hand side of their diagram. I followed your tutorials and had to remake all my ends to match their connector. Just an FYI. Minor gripe but truly I am so grateful and thankful for your tutorials

  9. Where is the plug wiring shown?

    1. The pug end is just going to be a standard 8p8c modular plug and the order of the wires is going to depend on the wiring standard used for your structured wiring. How the wall jack was wired. For TIA568A it will be white green, green, white orange, blue, white blue, orange, white brown, brown. If you're using TIA568B it will be white orange, orange, white green, blue, white blue, green, white brown, brown.