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Local Area Network Wiring Issues

The most frequent problem we have encountered with Local Area Networks is incorrect or bad cabling. According to statistics, 70% of all network troubles are related to wiring problems. Here are just a few of the problems we've seen:

1. Handmade patch cords
2. Re-using existing phone or terminal wiring for networking
3. Trying to run multiple services on different pairs of the same cable
4. Bad installation and pulling practices

1. Handmade Patch Cords Don't Add Up

Many people try to save money by making their own patch cords. In many cases this works out to just plain bad economics. First of all, there is more to making cables for networking than simply meets the eye. Since ethernet and Fast ethernet use signals in the 10-100 megahertz (million cycles per second) range, common sense electrical thinking is out the window. At these frequencies, phasing, interference, and impedance begin to have real effects beyond the simple electrical characteristics. Spending $15 dollars (or more) of labor and materials to make a cable that sells for $7 through mail order is just funny to us.

The most common mistake these do-it-yourselfers make is a wiring to plug mismatch. That is, they use solid wire with plugs meant for stranded wire (the cheapest and most common type). This may cause real hair-ripping problems with stations going on and off the network mysteriously, unexplained slowdowns, etc. Obviously, you can waste days chasing these ghosts around the network, without any real success. Stranded wire, which tolerates flexing and bending, is meant for patch cords. This unfortunately also limits the length of patch cords, since stranded wire loses much more signal per foot than solid wire (higher attenuation).You would be surprised at the number of people who are mis-informed about network cabling, including television shows (Tech-TV), computer and large-chain electronics stores (Best Buy, Circuit City, Comp USA), and consultants. A good way to find out if someone really knows what they are talking about is to ask them if they can explain the TIA/EIA 568 wiring standard. If they don't know it, run away fast, learn about it yourself.

The limit for patch cords specified in the TIA/EIA 568 wiring standard is 10 meters (about 33 feet) per run. This includes the station end (the jack) AND the hub side (patch panel) TOGETHER. The TIA/EIA 568 spec allows for 90 meters of standard cable (solid wire) to each station, for a total of 100 meters. These distances are based on the timing for ethernet, and the speed of electricity to travel that distance.. It is possible to run longer patch cords to each station, but this will greatly reduce the total distance per run allowed (We use 50% as a good estimate). Calculate the effect in this common example, one 50 ft patch cord (about 15 meters) at remote end, 15 foot (about 5 meters) patch cord at rack, 20 meters x 2 = 40 electrical meters or 120 electrical feet. Take a 70 meter (220 foot) horizontal run, and add the patch cord calculation in, and you have exceeded the limits. It might work anyway, but why take the chance? Keep patch cords longer than 20 feet under wraps for special situations and make sure you do the math. One of the symptoms of a network where runs are too long is excessive slowdowns, because by the time signals travel down the length of the wire ethernet gives up and thinks the message was lost, so it treats it as a collision.

2. Don't Gamble On Recycling Present Cabling

Old cabling may be the older phone type cabling, which is completely unsuitable for modern networks. It may in fact be Category 5 or better cabling, but without testing each run there is no way to know if the cabling is any good (see Bad Installation Practices). There may only be one run per station or room, which is not enough. Then there are the problems of the jacks, which might be damaged, missing, or improperly installed. It might have a PVC jacket, which is outlawed in most plenum-type drop ceilings. You need to use teflon-jacketed cable, which does not emit toxic fumes in the event of a fire. Finally, it is usually just laid across ceiling tiles instead of being fastened to some stationary points above the ceiling, which violates most building codes.

Most often the best use for old cabling is two-fold: First, it can sometimes be used to verify the length of a particular planned wiring run. Second, it can be attached to a group of new cables and used as a guide to pull four new cables. Wire is cheap, labor is expensive, saving wire by reusing the runs fails the economy test once you have to call a contractor back out to fix, replace, or add more runs. Do it once, do it right, or do it over (and over).

3. Multiple services per cable

Use only the standard wiring configuration, don't allow anyone to "manually" hack around putting phone lines on certain jacks. That is done by using an adapter at the patch panel.

4. Proper Installation Practices

To avoid stretching, pulling tension should not exceed 110N (25 lbƒ) for 4-pair cables.
Installed bend radii shall not exceed:
- 4 times the cable diameter for horizontal UTP cables under no load conditions.
- 8 times the cable diameter for horizontal ScTP cables.
- 10 times the cable diameter for multi-pair backbone twisted-pair cables under no load conditions.

Horizontal cables should be used with connecting hardware and patch cords (or jumpers) of the same performance category or higher.

Avoid cable stress, as caused by:
- cable twist during pulling or installation
- tension in suspended cable runs
- tightly cinched cable ties or staples
- tight bend radii
Important Note: Installed twisted-pair cabling shall be classified by the least performing component in the link.

Twisted-Pair Connector Terminations
- Pair twists shall be maintained as close as possible to the point of termination.
- Untwisting shall not exceed 75mm (3.0 in) for category 3 links and 13mm (0.5 in) for category 5e and higher links.
- Connecting hardware shall be installed to provide well-organized installation with cable management and in accordance with manufacturer's guidelines.
- Strip back only as much jacket as is required to terminate individual pairs.
- Terminate each horizontal cable on a dedicated telecommunications outlet, that's a jack NOT a plug.