Category Wiring: What You Need to Know

The fundamentals of twisted pair wiring for today's communication technologies.

By Fred Harding
December 05, 2007
I've said it before, and I'll say it again. Twisted pair wiring may well be the wonder drug of the information age.

Twisted pair wiring, in its most common state, consists of four pairs of 24-gauge solid copper wiring. It's called Category wire, with the number following the category indicating the speed at which data can potentially travel.

Most everyone today uses Category 5e wiring, aka Cat 5e, for data, control signals, voice and, increasingly, transmission of video and audio signals. The wire will have a blue and a white-blue pair, an orange and a white-orange pair, a green and a white-green pair and a brown and a white-brown pair of conductors.

The higher the category rating, the more you'll discover variances in the twist rates on the individual pairs. If you were to take your wire stripper and remove the outer overall jacket and then straighten out each of the pairs of wiring found inside, you'd discover that the wire itself is the same thing.

The twisting of the conductors helps increase the speed at which data can travel down the wire. It also is an effective shielding strategy, which, for voice applications, translates to less cross talk between phone lines.

EIA & TIA Standards

Twisted pair wiring is terminated most commonly using standards developed by the Electronics Industry Association and the Telecommunications Industry Association.

These standards are called EIA/TIA 568 A or B. The difference between the two methods is in where the orange/white-orange and green/white-green conductors are placed on the jack or plug.

Traditionally, the data industry has followed the B standard, and the voice trades the A. If you are wiring for residential applications, where it's possible the jack might be used for voice or data in the future, the A scheme makes more sense.

The A scheme places the blue/white-blue and orange/white-orange conductors in the conventional line one and line two position on the jack.

Regardless of which scheme you choose to use, it's important to follow what the associated equipment manufacturers recommend.

This is extremely important on control systems, where a keypad might have a punch down strip on the back, with a RJ45 jack on the equipment end. You'll find the specific recommendation on connection style in the installation manual for the system.

Don't assume that it's an A or B; when in doubt, check.

Things to Keep in Mind

When you're installing Cat 5 or higher wiring, it's important to understand some of the requirements around handling the wire.

If the wire is pulled too hard, cinched too tight or bent at too sharp a radius (to name a few possibilities), the performance of the wire can be affected.

For voice applications, extremely rough handling can lead to breakage of the fragile conductors. This is the concern.

Where some of the more restrictive covenants really have an effect is on data wiring. If you are trying to deliver a network installation to a particular standard, improper handling will lead to troubling loss of potential speed.

Other things to avoid include:
  • More than a 25-pound pull on the wire. I myself am not sure how to test that. So, I suggest that if the wire isn't flowing smoothly, you're probably over the pull limit.

  • Bending the wire beyond a 1-inch radius.

  • Using staples that will compress the wire.

  • Cinching your zip ties too taut. Velcro strips are preferred when working with bundles of wiring because, inevitably, you will want to add another length or two of wire after you dress your bundle.

  • Overstuffing wire into conduit.

Also, when punching wires down on jacks, or crimping a plug, take care not to remove too much of the outer jacket, and don't untwist the pairs more then you actually need to.

On the positive side, it is strongly recommended that you label all your wires so you can identify them in the future.

Running your wire over a pulley system will save wear and tear and maintain integrity; consider this if your wiring path is likely to include a sharp bend.

Also, if you don't have a tester, consider getting one. Remember: tools are tax deductible.

Better quality testers will give you a visual indication of the state of your wire and jacks.

Typical information includes determinations as to whether you have an open conductor or two, whether you have pairs reversed, whether there's a short on the line or other mis-wiring possibilities.

Better quality testers will feature a time delay refractometer, commonly called a TDR, which will show the number of feet to a break on the cable.

Punching Wire Down

Terminating wire at jacks is done using a punch down tool. Jacks will have the 110-style of connection.

Each wire will have its own color-coded slot. So, the guesswork is eliminated.

When you want to punch a wire down, remove the outer jacket only, separate out the individual pairs and, then, lightly press the wire into the slot.

Using a 110 tool, you'll push the wire down against the knife blades in the slot, effectively stripping the insulating jacket off the wire and seating the wire into the blades. Don't use a screwdriver for this job.

Better quality 110 tools will offer the installer two blade options: one that simply presses the wire into the blades and one that also trims off the excess short bits of wire that you would otherwise need to trim with a set of cutters.

If you've got a lot of punching down in your future, get one of the 110 tools that is an impact style. The mechanism will be easier on your hand after a full day's work.

The other style of punch down, commonly used for voice applications, is a 66-style block. The concept for holding the wire in place is similar to the 110 block in that the jaws on the block strip hold the wire in place.

Note that 66 blocks are not usually labeled and require a different blade then a 110 style to terminate the wire.

Regardless of which style block you use, do not stack wires on top of one another in a slot.

The outward appearance may be a satisfactory connection, but you're sure to have a service call back if you try and cut that corner.

Fred Harding is in sales and technical support at Capitol Sales (, a full service distributor of electronic installation hardware.

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