Sunday, August 7, 2011

How to Wire Cat5 Ethernet Cable for 100Base-TX

I'll answer your first question first: why not 1000Base-T? Well, the simple answer is that 100Base-TX requires 4 wires whereas 1000Base-T requires 8. While 4 more wires may not sound like much, I've found it exponentially more difficult. With 4 wires, I feel that I have good individual control. With 8, there always seem to be one or two wires with a mind of their own. And, how often do you need more than 10 megabyte transfer speeds?

Next, your second question: why would you want to create your own Ethernet wire? Why can't you just buy pre-made? This answer comes in two parts: (1) it's fun, and (2) I never seem to have the right length on-hand. When 14 feet is required, 10 feet doesn't cut it and 25 feet seems like overkill. Sure, in some cases, the right size can be ordered, but I'd rather make it on-the-spot than wait for delivery. And, some sizes simply aren't sold.

Do I have your attention now? Good. To make your own cable, you'll need 2-3 tools (in addition to some raw cable):

  1. RJ45 crimper (appx. $20)
  2. RJ45 connectors/jacks (appx. $10 for 100)
  3. wire cutters (appx. $20) (optional)
The crimper has blades to cut your wires, but I prefer a pair of good wire cutters like the linked ones. Once you have your tools, you'll need a good diagram of how to align the wires. I like the diagram in this How to Wire Ethernet Cables page. Hold the connector with gold pins up, opening close to you and release lever on bottom. Pin 1 is on your left, pin 8 is on your right. You only have to connect four wires (T568A):
  • pin 1: white/green
  • pin 2: green
  • pin 3: white/orange
  • pin 6: orange
You can cut off the four brown and blue wires---you don't need them for 100Base-TX. Once you've managed to align the wires into the correct pins, make sure the casing is in the connector far enough that it will be clamped inside the connector when crimped. Also, make sure the small wire extend all the way to the end of the connector---I check this by looking on the bottom of the connector (release lever side). If everything looks good, insert the connector with wires into the 8 pin socket of the crimper and press down hard. Be careful of the blades on the crimper. Do this on both ends and you should have successfully made your own 100Base-TX. Of course, it's quite possible (likely?) your first attempt will fail, so start with a short wire and test it. In my experience, it's easy after you've made one or two wires.

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