Avatar of cebu1014
 asked on

Cat5 to rj11 plug

Blue and white/blue pair is used for line 1  I am assuming. Only need one line anyway. Where do I connect on a 4 post modular jack? Can I also  just punch the wires directly from cable to rj11 plug? If so what pins?
ComponentsNetworking Hardware-Other

Avatar of undefined
Last Comment
Steven Carnahan

8/22/2022 - Mon

You don't have to punch the cables yet...why not use alligator clips and butt set to test what cables you need?
Steven Carnahan

Usual configuration is:

Blue - pin 3
Blue/White - pin 4

Orange/white - pin 2
Orange - pin 5

At least that is the configuration that we use.
Michael Dyer

Typically, telephone jacks are wired from the inside pair out.  So for a 4 pin setup, the first pair would be on pins 2 and 3, and the second pair would be on pins 1 and 4.  Exactly which wires go to which pin on the 4 pin jack does not matter as long as they are all done exactly the same.
I started with Experts Exchange in 2004 and it's been a mainstay of my professional computing life since. It helped me launch a career as a programmer / Oracle data analyst
William Peck
Steven Carnahan

@Equitrac_Michael:  Thank you, I am trying to do to many things at once today and was a bit to hasty in my answer above.  

We actually use RJ45's for all our jacks since an RJ11 plug will go into an RJ45 jack. We just color code or lable the jacks that are used for voice/fax vs. data. And since the cable runs to a patch panel in the back room you can punch down the Catx cable the same regardless.

OK thanks. What i have is modular jack for fax machine in office. I was planning on using the blue wires  from a cat5 run and wire them to the modular jack of fax where already existing wires are attached  in jack . The other end of run is about 175 feet to a register in building that has credit card machine. The extended fax line via cat5 will be rollover for authorizations in case DSL goes down.  Fax is rarely used anyhow. This sound OK?

I dont go to the store often so I was planning ahead on what I needed to do.
Steven Carnahan

Something that you could do (I don't necessarily recommend this approach however because of the additional points of failure) is to buy an RJ11 splitter, a short standard phone line, an RJ45 coupler and the existing ethernet (CAT5) cable.

1. Plug one end of the ethernet cable into the coupler and the other into the device you are connecting
2. Plug one end of the standard phone line into the other end of the coupler and the other into the splitter
3. Unplug the fax phone line from the wall jack and plug it into the other jack of the splitter
4. Plug the splitter into the wall jack


Get an unlimited membership to EE for less than $4 a week.
Unlimited question asking, solutions, articles and more.

I will see about it . Thanks.  Question(and curious):
If both ends of cat5 are attached already to say a modular rj11 phone jack , could I run a standard phone line from the modular jack(the fax) to the nearest modular jack attached to the cat5 cable?? The other end of cat 5 cable in other location would serve as end to attach device...

 In other words no coupler from your example, just a modular jack.
Steven Carnahan

Log in or sign up to see answer
Become an EE member today7-DAY FREE TRIAL
Members can start a 7-Day Free trial then enjoy unlimited access to the platform
Sign up - Free for 7 days
Learn why we charge membership fees
We get it - no one likes a content blocker. Take one extra minute and find out why we block content.
Not exactly the question you had in mind?
Sign up for an EE membership and get your own personalized solution. With an EE membership, you can ask unlimited troubleshooting, research, or opinion questions.
ask a question