Question: Can I Use Cat 5 Cable for Networking and Telephone at the Same Time?

I have been checking the wiring at my house and found out the phone wire is Cat5e. I popped a few face plates to check it out and noticed that a few of the twisted pairs were not connected. My question is two fold; why was it not connected and if I decide to connect the wires (to run lan) will the cable still work for phone (for resale value)?

-Drew H.

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Bridgette Farley says:

We added a large addition over our basement garage. Our original phone lines coming into the house were small and old. They had been spliced into in several areas. Many have been disconnected except for one in our bedroom that is used to connect our Uverse modem, which also gives us connection issues with speed. Now is the perfect time to wire new lines for phone, data and coax since there isn’t sheet-rock up yet. We have combed the internet trying to understand how to do the installation from start to finish and there isnt anything real clear on the complete process, or its confusing. We’re planning on running CAT6 cable throughout our house. The way I’m understanding things is that each cable has to run independently from the wall back to a designated area (closet, source box, switch, patch panel) We found that the most neutral place to pull all these cables back to in our basement area where it can be managed and out of the way.Is this right? ie: If 3 cable boxes are installed in our living room the 3 cable wires need to go into our designated basement utility area and into a switch? and repeat with each room running it back from that room to the basement area. How do you tie this to your outside telephone interface box? Do you run a Cat6 from it into the basement utility area where all the feeds come in?

Mike C says:

Dont follow his advice. Never put Rj11 into Rj45 port. He doesnt know what he is doing. Instead wire you cat5e and rj45 for telephone service. How are you going to plug an rj11 jack inside a bigger rj45 keystone and make it work.

You Don't Say? says:

You can also split cat5 cable into two jacks for two separate data connections by utilizing all 4 pairs of wire. Probably increases more dropped packets but in my own personal experience there’s no discernible problems with it.

KalishAlexander says:

Using one cat-5 cable for both data and telephone at the same time is what we often do in Russia an Ukraine (we’re all hardcore, you know:D) and it works well. You can actually use one cat-5 cable for 1 data and 2 telephone connections at the same time, but it will have a downside – the speed for data connection will be limited to 100MBits and you will not be able to use PoE. It’s possible because a 100MBit standard only uses two of four cat-5 cable’s pairs – the yellow(yellow + white&yellow) and the green(green + white&green) ones, so the brown and blue pairs can be used as telephone pairs. You just need to replace a single wall socket with double rj-45 + rj-11 socket, connect the wires properly on both sides and it will work, if only 100Mbit is enough for you.

Drew H says:

Thanks for the info Eli,
Thankfully we got a great company to wire our house when it was built, so all the phone lines go into a switch. Now if only the same could be said of the company who  build the roof…

Drew H

ShizoUn1 says:


flukeman022 says:

I bought this Ethernet splitter from Amazon to connect my BT Hub (router) to the internet and telephone but one of the two RJ45 female is faulty so i asked for my money back but because i wanted it for phone and internet the seller refused to give my money back saying I’m using it wrong it is for LAN not WAN.  However even when I listen to what he said it is designed for LAN I connected my laptop to my PC and I got the same result one of the female RJ45 is faulty. So my question is the seller telling me lies and can CAT5 be used to connect to the internet? or is the seller correct?

68908-GB Pinout 2 x CAT5 Ethernet 1 x RJ45 Plug to 2 x RJ45 Jack

Product Description
Other Characteristics:
Cable length: 0.15 m
Cable standard: Cat5
Colour of product: Grey
Ethernet LAN (RJ-45) ports: 3
Gender: Male/female
RJ-45 input ports: 1
RJ-45 outputports: 2
Wall mountable: Y

Manufacturer’s Description
Pinout 2 x CAT 5 Ethernet 1 x RJ45 plug to 2 x RJ 45 jack
CAT T-Adapter 2x 10/100 BaseT

Usable as port doubler for Cat 5 connections
suitable for 10/100Mbit network connections

RJ45 plug RJ45
jack1 RJ45jack21 1
2 2
3 3
6 6
4 1
5 2
7 3
8 6
lenght 15 cm
laenge 15 cm

Any advice will be much appreciated

qoaa says:

I have cat5e running from NID outside back of house to a single phone jack (my apartment has just a single jack)
on that jack I have bonded vdsl2 50 megabit down 10 megabit up, plus a normal landline as well all off the single cat5e from NID outside to my one jack.

I didnt realize it could do both bonded vdsl2 with 2 lines at 25/5 combined to make 50/10 while still having a landline with all the extras like caller ID, 3 way, etc

Rhys Edwards says:

You can split the cable for data and calls but it won’t support 1 gigabit any longer

Derek Blockcolski says:

If I were to utilize my cat5 that’s being used for my internet which is only on white/blue pair, how could I use 2 of the other color pairs to use Ethernet somewhere else in the house? Where would they need to be punched down on the jack?

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