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Quick and Inexpensive way to double your network wires

luc_roySystem Admin
 One of the main issues with network wires is that you never have enough.  You run plenty and plan for the worst case but you still end up needing more.  What many people do not realize is with 10BaseT and 100BaseT (but not 1000BaseT) networks you can double your network size by splitting the network wires.

  No matter what standard you are using (A or B) on 10/100 networks only pins 1, 2, 3 and 6 are used.  The most used standard is B so this means that only orange/white (PIN 1), orange (pin 2), green/white (pin 3) and green (pin 6) are used.  This leaves you with 4 extra wires.  Now this is only true if you are not using Power Over Ethernet (POE).  POE uses the other wires to provide a low voltage power to end user devices such as phones, wireless access points and cameras.  This however can also be overcome as discussed later in this article.

  The simplest way to do this is to purchase a CAT 5 splitter.  These are readily available on the internet. The best part is that are inexpensive now and they are plug and play.  Most companies label them with letters or to identify what you have connected on each end.  The only downside is you end up with this ugly box hanging on the outside of your wall.  The up sides are speed and the ugly box lets you know it has been split.  You can find these from most major cable manufacturers for anywhere from $8-15 dollars.

  If you are a handyman you can make this yourself and save a bit of money and time.  I like to make them myself in building installs because you can finish them off with a nice face plate and it looks professional.   The biggest thing to remember is the colors you used for the second connection.   My recommendation is to line brown up with orange and blue with green because they are similar and easy to remember.  In doing this your jacks will always be wired using the following wiring plan

Port A:
pin 1- orange/white
pin 2 - orange
pin 3 - green/white
pin 6 - green

Port B:
pin 1- Brown/white
pin 2 - Brown
pin 3 - Blue/white
pin 6 - Blue

  Our last hurdle is the use of POE.  By removing the 4 wires used for POE we now cannot push POE on our network wires.  This problem is easily resolved by using a Power Over Ethernet Injector.  On the end user side of the computer we can install a POE Injector to push power into the required device.  When the user connects their cable into the injector it will be an 8 wire cable.  The data will simply pass through the injector and the 4 new wires (Pins 4,5,7,8) will have power applied to them by the injector.

  Remember because you are not pushing POE there is no need to connect these to POE ports.  If your switch is only POE then consult the manufacturer instructions on how to turn the POE feature off on these ports.  This will conserve power and allow for its use on other devices.

  The ability to split wires is extremely useful in home applications.  Most new homes come with CAT5 or 6 ran for phone lines.  By splitting them you can still maintain a phone jack but now have a network jack in each location.  This allows you a lot of flexibility in termination of your wiring.
luc_roySystem Admin

Comments (4)

luc_roySystem Admin


added that it only works for 10 and 100 networks.
Author of the Year 2011
Top Expert 2006

A nice informative Article.
Thank you for putting it together.

"Yes" vote above.
Roger CraneNetwork Engineer

WOW! I can't believe that this actually got posted on EE!

I worked at a medical clinic, where the IT guy had done this to connect an extra PC in 4 different offices. I was totally shocked, when I saw this. I thought that it was the dumbest thing that I had ever seen! The craziest part about it. It actually worked, or so it seemed. It worked just like running a 375' cat 5e cable between two buildings to provide Internet access for two PCs.

My understanding of the electrical nature of this connection is that the two unused pairs help with eliminating or reducing noise on the data pairs. If you add another communication signal, then you are effectively adding noise into the circuit. Not on just one data communication link, but two.

There is already the possibility of crosstalk between the positive and negative pairs. Think NEXT and FEXT! Near End Cross Talk and Far End Cross Talk for those unfamiliar with the terms.

The addition of another communication signal just exacerbates the problem. Not only do you have to worry about NEXT and FEXT, but the noise (EMI) generated by the additional current flow.

Sure it may work, though the throughput may not be ideal. Due to the addition of noise and EMI the signal and therefore the data is bound to become corrupted. This will result in retransmission of packets by TCP.

So where is the benefit? Just run another cat 5e cable. Do it right!!!
Brian BEE Topic Advisor, Independent Technology Professional

Glad you clarified about the fact it only works on 10 or 100. I would put this in a big bold disclaimer at the beginning because most equipment nowadays is gigabit and the type of end-user who might try something like this probably wouldn't know the difference. I would never split wires in this way for the reasons already explained above. Interference could cause all sorts of unknown problems that an end-user would have trouble identifying. Either run another cable, or use wireless before splitting cables.

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