"Basic Classifications"

In theory, there are several classifications of copper cabling systems available for datacom applications today. In fact,the EIA/TIA-568-A standard (see .EIA/TIA 568-a standard) defines five categories or types of copper cable and components:

	Category 3 -16 MHz, 100 ohm. unshielded twisted pair.
	Category 4 -20 MHz, 100 ohm, unshielded twisted pair.
	Category 5 -100 MHz, 100 ohm, unshielded twisted pair.
	Type 1 - 20 MHz, 150 ohm, shielded, twisted pair.
	Type 1A - 300 MHz, 150 ohm, shielded twisted pair.

    The reality, however, is that only one-Category 5-is in widespread use at this Lime. In fact, Cat 5 has become synonymous with copper (as opposed to fiber optic) teledata systems.
    The reason is simple: speed.
    Category 3 cabling, at just 16 MHz, was originally intended for slower computer networking protocols like old-style Ethernet. But as data applications speeded up, Cat 3 soon became too slow for anything but voice telephone communications.     Rather than moving up to the next level of bandwidth-the 20 MHz Category 4 systems-most data network specifiers and users jumped directly to Category 5 for significantly greater speed. As a result, no Cat 4 cable has been seen out in the real world for a couple of years now.
    What's more, as prices for Cat 5 cable and components have dropped, many installers now use Cat 5 for all voice systems as well as data systems, virtually eliminating Cat 3 from the market.
    Types I and IA, meanwhile, are special-purpose four-conductor cables de signed for particular computer networking protocols. They have never achieved widespread acceptance. however.

- This article was written by Brooke Stauffer.

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