Building Your Own Ethernet and Crossover Cables

I got this information from which is run by those great Ambrosia Software guys. That page is gone, but I found a better page with updated info:

In fact, it obsoletes this page. So go there after reading this one.

Why bother crimping cables? I dunno. The prebuilt cables are generally more reliable, and are only twice as expensive, which is still pretty cheap. It costs around $2 to crimp a cable, in my experience, due to labor costs. However, there are certain things you can't do with precut cables. You can't have precise lengths along the walls. You can't have very short cables, useful for wiring up racks. Bulk cable also pulls out straighter, so it's easier to bundle them into thick cables.

There are three wiring standards: T568-A and T568-B, aka AT&T, and TIA/EIA-568-C, which we don't cover.

T568-A is: GR/WH - GR - OR/WH - BL - BL/WH - OR - BR/WH - BR

T568-B, aka AT&T is: OR/WH - OR - GR/WH - BL - BL/WH - GR - BR/WH - BR

B used to be more common in my part of town, but lately I've decided to use A because it's considered the real standard. Little did I realize, becase here's a weird thing: the B standard says to use the A wiring. Now, the C standard has eliminated B wiring entirely. Some of us are slow to learn.

That's looking at the plug from the "flat" side (the side opposite the plastic tab). (Actually, it doesn't matter, as long as you're consistent about which side you look at.)

Both plugs are wired identically.

The crossover cable has TIA-A on one end, and TIA-B on the other end.

Simple enough? If not, try the URL above, where they go into greater depth, and provide illustrations.

More Advice

The current best-of-breed crimper is the Platinum Tools EZ-RJ45. It's got better leverage than the prior king of the hill, the Ideal Telemaster.

The EZ also takes these patented plugs that are easier to crimp, because the wires shoot through the entire plug - you can review your work before crimping. In my experience, this saves a lot of time on the first day, when you're getting used to the wire. Once you're used to it, you can do just as well with the old fashioned RJ-45 plugs.

I like to strip extra insulation off the cable, then arrange the wires, and then trim them all the same length. It's neater.

Test your cables by running actual data over them. I had a batch that tested against a simple wiring tester, but flaked out on data, because the plugs (the "ends") were faulty. I had to cut them all off and get refunds, then get another batch from another store.

Don't kink the cables. Problems seem to develop at the kinks, over time.

"Plenum" meets a building fire safety code for wiring that's in the ceiling (and within ducts). If you're installing overhead wire in an office, it must be plenum. If you use regular (cheap) cat5 cable, you're creating an unsafe work environment, and probably voiding the insurance.

To pull new cable (if you have it in a conduit) hook the old cable onto the new cable, and tape it up tight with electrical tape. Grease it up with that cable lube, and from the other end, pull on the old cable. If you're lucky, the new cable will pull through and replace the old cable.