Put together your own ethernet cables

Friday, February 11th, 2011 by William Gannon (See all posts by William Gannon)

If you work as a computer networking professional, you should know how to make an ethernet cable.  Creating your own cables can help reduce cable clutter by making cables that are only as long as they need to be.  Sometimes you only need a very short cable; other times, you need an extra long cable.  You may find yourself in a situation where you need to apply a new RJ45 connector to a broken cable end.  This article will show you how to put together a standard ethernet cable.

Before you get started, you’re going to need a few supplies.  At the very least, you will need an RJ45 crimper, something to cut cable, a length of ethernet cable, and an RJ45 connector.  The crimper punches the contact points of the RJ45 connector into the individual wires of the cable and sometimes has extra features like the ability to cut a cable or remove a cable’s outer jacket.  An RJ45 connector is the kind of connector you will find on a standard CAT5 or CAT6 ethernet cable.

RJ45 connector

First, you need to decide how long your cable is going to be.  You should compensate for the fact that you’ll be cutting at least several inches off both ends; six inches to a foot extra on both ends is safe for longer cables.  Finishing a cable only to find out it is a bit short of what you need can be very annoying.  Also consider any kind of possible obstacles in the pathway of the cable and any planned cable management to be used on the cable when deciding on the length.  Cut the cable when you have determined the length.

Next, you need to remove the outer jacket of the cable to access the individual wires inside the cable.  Most crimper tools have a part with blades for the purpose of cutting into only the jacket and removing it; you need to be careful using this method because it is easy to cut too deeply and damage the contact wires.  I prefer to take a small pair of scissors and cut a line into the outer jacket from the end of the cable to several inches inward. 

Once you have removed the outer jacket, you should see four pairs of twisted wires and possibly a central spine and a string; the spine keeps the pairs of wires separated, and the string can be used to cut a line into the jacket by pulling on it.  Inspect the individual wires to make sure that you have not damaged or nicked them at all.  A damaged cable can seem to work at first, but may cause problems later on.

Cut off any excess parts of the outer jacket, the central spine, and the string.  Untwist the pairs of wires; wires inside the cable are twisted to prevent cross-talk between wires.  Straighten the wires as much as possible using your fingers to firmly pinch and run over the wire.

Align the individual wires next to each other in the proper order.  The most common wiring scheme for CAT5 and CAT6 cables is called 568-B wiring; the other common wiring scheme is called 568-A.  To create a standard, straight-through cable, used for connecting computer network interfaces to a switch, router or modem, make both sides of the cable 568-B or make both sides of the cable 568-A.  If you are making a crossover cable, for say connecting two computer network interfaces to each other directly, make one side 568-B and the other side 568-A.  The RJ45 connector has eight pins.  The pins would be ordered one through eight if you had the pins face up.

568-B wiring order: White-Orange, Orange, White-Green, Blue, White-Blue, Green, White-Brown, Brown

568-A wiring order: White-Green, Green, White-Orange, Blue, White-Blue, Orange, White-Brown, Brown

568-B wiring diagram

Make the individual wires as straight as possible; cut a straight line across the ends of the wires.

Next, place the individual wires into the RJ45 connector keeping them aligned, straight, and in order.  If possible, try to get a bit of the cable that still has the outer jacket into the connector.  I have the kind of RJ45 connectors that allow you to push the wires into it and through the other side; I can cut off excess length after pushing the wires through.  Some connectors come with an insert to make it easier to align the wires inside of the connector; if you don’t have an insert, it may take some practice to get the cable to properly go through the other end of the connector, but it’s possible.  The best method is to hold the wires while together while slowly pushing them along the bottom of the connector towards the openings on the other side.  If you have the kind of RJ45 connector that is closed on the other end, you’ll need to cut the lengths of the wires to about the length of the RJ45 connector.  Any straigthened length of wires can be susceptible to interference and cross-talk.  You might consider putting boots onto the ends of the cable before putting the connector on; an RJ45 cable boot can protect exposed wires and keep things from getting caught on the release tab of the RJ45 connector, but they are ultimately optional.  If you are going to use boots, make sure you put them on the cable before putting on the RJ45 connectors.  I put boots on my cable, but I didn’t slide them into place until I was finished.

RJ45 cable boot

Double check to make sure the wires are still in the proper order.  When you have verified that they are, it is time to crimp the cable.  Place the end of the cable into the RJ45 opening on the crimper tool; make sure the end goes all the way in so that the contacts will be pushed into the cable.  Once the cable is in the crimper, squeeze the handles of the crimper tool together.  Make sure that you have used adequate force so that the contacts of the connector go all the way through the wires.  The contacts of the connector should be pushed up into each individual wire.  If you notice that a contact is only part way through, put the cable into the crimper again.  Once the cable has been crimped, you just need to get rid of the excess length of the wires on the other side.  I have a crimper tool that cuts off the excess while crimping the cable.  If your crimper doesn’t do that, you can twist every individual wire until they come off.

You should now have a finished cable.  Making cables requires practice, so don’t get discouraged if your first attempt doesn’t turn out how you had hoped it would.