Friday, March 18, 2005

What does AWG mean?

AWG stands for American Wire Gauge, and it is a standard used for denoting wire conductor diameter. The system is counter-intuitive, so the lower the AWG, the thicker the conductor.

Actually the system is even more counter-intuitive than that. Once you get to wires thicker than 0 AWG, you do not use negative numbers. Instead you just add more zeroes and end up with wire sizes like 00000 AWG, or, written another way, 5/0 AWG.

If you pull a telephone or computer line out of the wall and snip off the end, chance are good that you'll be looking at conductors that are between 0.016 and 0.025 inches across which is 26 to 22 AWG. (That's 0.4039 to 0.6452 millimeters for the metric-ly inclined.) If you go home and rip a power line out of the wall for a snip--a very bad idea, you'll probably see conductors between 14 and 12 AWG.

The thicker the wire, the lower the AWG, and the lower the resistance per unit of length. For more information about load carrying capacity and the relationship of conductor diameter to AWG, visit Power Stream: Wire Gauge and Current Limits.

Thursday, March 17, 2005

What UTP pairs do I use on a phone jack?

There you are with a four pair wire, and a six conductor phone jack that has terminations for only three of the pairs. Which pair gets left out? It helps to look at a list of pair designations:

Pair 1: blue and white
Pair 2: orange and white
Pair 3: green and white
Pair 4: brown and white

If you're wiring only three pairs, you use the first three. If you're wiring only two pairs, you use the first two. That's easy enough. But sometimes things get more confusing and you have to terminate quad wire onto a Cat 3 jack or attach Cat 3 or Cat 5e cable to a telephony plate with quad wire screw terminals. In those cases you need to know how the quad wire conductors and Cat 3 or Cat 5e cable conductors match up so that you can translate between the coloring schemes. You may run into "quad wire" that has six conductors; the additional two conductors (blue and white) are included in the list below:

Red: blue conductor of the blue and white pair
Green: white conductor of the blue and white pair
Yellow: orange conductor of the orange and white pair
Black: white conductor of the orange and white pair
Blue: green conductor of the green and white pair
White: white conductor of the green and white pair

Wednesday, March 16, 2005

What does RJ-45 mean?

Many people use the term "RJ-45's" to refer to Cat 5e jacks or Cat 5e plugs. This is not, however, always the case.

RJ-45 jacks and plugs have 8 pins. If you have a computer patch cable laying around, you can see them on the plug. (Those shiny metal lines on the end.) RJ-45's are sometimes referred to as 8P8C connectors. This stands for 8 Position (which describes the width) 8 Conductor (or 8 Connector depending on who you talk to).

There are many different types of RJ-45 jacks available including Cat 3, Cat 5e, Cat 6 and USOC (regular telephone). Usually your supplier will know which one you're asking for based on the type of wire you've purchased, but it doesn't hurt to check. Make sure that when you ask for RJ-45's, you get what you want by indicating the specification that you are trying to fulfill.

UPDATE: Thomas of TECHtionary 2.0 points out that some people may be curious as to what the "RJ" of RJ-45 stands for. It's short for "Registered Jack." Check out his site; it's definitely worth a look.

Tuesday, March 15, 2005

How far can I run Cat 5e or Cat 6?

The standards for Cat 5e and Cat 6 call for a maximum run length of 90 meters or 295 feet. While you may make a longer run and get it to work, this is not recommended. Even if problems don't show up immediately, they may come up later as your computers are upgraded to transmit faster or your network is expanded. If you must make a longer run, you can either put a signal repeater in the middle of the line or you can make your long run with fiber optic cable.
If your run is between 295 and 590 feet, the repeater option may be the best option for you. A switch or hub will act as a repeater. Make sure that you locate it in such a way that both runs on either side of the repeater are within the 90 meter standard. It won't do much good to split a 500 foot run into two runs of 100 and 400 feet.
If your run is longer than 590 feet or if most of the run is outside, fiber optic may be your best option. You'll need a media converter or fiber fed switch at each end of the fiber run to convert your network signals back and forth between electrical signals on copper and light pulses on fiber. If you are running fiber optic cable underground, you'll need to protect the delicate glass fibers inside the jacket by running it through a conduit or by using armored fiber optic cable.

UPDATE: Here's some clarification on the 90 meter maximum run length. This is generally cited as the maximum horizontal run length. The max length from switch to node is 100 meters. This 100 meter length, however, includes the vertical drops and all passive links such as the patch cables from the switch to the patch panel and the patch cables from the jacks to the computers (or other types of nodes). Big thanks to Marc at Lockergnome for calling the need for this clarification to my attention.
UPDATE: I have deleted hubs as an option to be used as repeaters. A very helpful email from Steve Anderson of BIP Solutions explains:

Hi, just read the clarification, and thought I should mention that the run length includes hubs as well.

It's to do with the maximum distance between active nodes. Nodes with store and forward will extend the maximum distance.

The limit's imposed by the time it takes for the smallest packet to be entirely on the wire. If a packet is entirely on the wire, and the beginning hasn't been accepted by all other nodes in the same collision domain, then you could have one begin transmitting and corrupting the other packet. The real problem is the original node doesn't know this has happened, so will only retransmit it if requested.

Friday, March 11, 2005

What is a KVM switch?

A KVM Switch is a keyboard, video, and mouse switch. It allows you to control more than one computer with the same keyboard, monitor, and mouse. Why would you want to do this?

A KVM switch comes in handy when you own and use more than one computer, but you don't want to cover your desk with or pay for a bunch of input devices. If you have an old computer that you'd like to access regularly, this is the perfect application for a KVM switch. Just set up the old PC near the new one, plug in your KVM switch, and both computers are accessible to you anytime. Some two port KVM switches even come with built-in cables.

KVM switches are a must in large network setups with several servers. No reason to take up space and go through the expense and hassle of setting up sixteen monitors and keyboards when you can just pick up sixteen port KVM switch. You can even get rack mountable configurations.

Thursday, March 10, 2005

What type of wire should I use for my phone system?

In the past people used quad wire, or POTS wire. This wire is not twisted, is susceptible to interference, and is not suitable for telephone systems with several lines. If you are updating an old system and you encounter this wire, your best option is to replace the old wire with some type of twisted pair wire, such as Cat 3 or Cat 5e, rather than expanding the system with the quad wire in place.

Most installers have been using Cat 3 for phones, but Cat 3 is getting harder to find, and the price difference between Cat 3 and Cat 5e has narrowed considerably to around five dollars per thousand feet. Cat 3 is still recommended for phones, but if there's any chance that your phone system may be used for data transmission in the future, an upgrade to Cat 5e would be well-advised.

Aside from future-proofing, there is another reason that some people use Cat 5e for phones: simplicity of installation. If you are wiring for a computer network at the same time that you are wiring for a telephone network and the job is very large, you may find it easier to contend with one type of cable rather than dozens of boxes of different kinds. There is truly nothing worse in an installation than pulling a long run, especially one that requires fishing through small conduits and around tight corners, only to find out that you pulled the wrong cable.

There are a few installers who use Cat 6 for telephone systems. Unless the phone network may be used as a computer network in the future, this is a strange choice. It is the equivalent of using a speed boat to cross a swimming pool or using a chainsaw to remove a small twig from a bush--it's very unecessary, very expensive, a big hassle for what you're trying to accomplish, but it will work.

Wednesday, March 09, 2005

Can I use Cat 6 cable with Cat 5e jacks and patch panels?

For a system to be rated at Cat 6, all of the components in the system have to meet the Cat 6 standard. However, Cat 6 is fully backwards compatible with Cat 5e, so if the system's technical rating is of no concern to you, feel free to use all of the Cat 5e components you want.

Using Cat 6 cable with Cat 5e components is a great way to future proof your network if your budget is limited. Jacks and patch panels are relatively easy to switch out in the future if you leave enough slack in the cable that you can cut off the component ends and reterminate the runs. Cable is a bit tougher to change out once the walls are up.

Tuesday, March 08, 2005

What is a jack? How do I install one?

Put as simply as is possible, jacks are the ports where you plug things in. Want to connect your computer to your Cat 5e network? You need a jack. Want to plug in the television and watch cable? You need a jack. Want to plug in your speakers to your new Dolby Digital 7.1 Surround Sound system? You need a jack.

Jacks look and connect differently depending on what they are for. Here is a picture of three keystone style jacks and a penny:
Three jacks around a penny.  Penny is roughly the size of the face of a jack.
From left to right we have a Cat 5e jack, a Coax BNC jack, and a Cat 3 toolless jack.

In this picture, the port of each jack is facing the camera. The port is where you plug in your equipment and is the part of the jack that remains visible after the jack has been installed. The back side of the jack faces inside the wall. To better illustrate this, here is a picture of two jacks that have been installed in the offices:

You can see how once the jack is snapped into the plate and the plate is attached to the wall, you can only see the port. You'll have to excuse the old school wall plate. (The much more attractive ones that we currently carry can be found in the wall plates section of In case you're curious, that is a phone cord coming out of the yellow Cat 5e jack. In our offices, we use Cat 5e for our telephone system and Cat 6 for our computer network.

The back side of the jack is where the hardwiring in the walls is terminated. Watch for future blog posts explaining how to terminate many different types of jacks.

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