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Category 5 UTP Cable

In theory, there are several classifications of copper cabling systems available for data communication applications today.  In fact, the EIA/TIA-568A standard1 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
Category 5 cable is constructed using eight 24 AWG insulated conductors (four pairs), enclosed by a thermoplastic jacket.  Each of the four conductor pairs is twisted together at a slightly balanced high-speed communications circuit and to reject electrical interference or "noise" from sources such as power wiring, fluorescent and HID ballasts, motors, and so on.

The reality, however, is that only one - Category 5 - is in widespread use at this time.  In fact, Cat 5 has become synonymous with copper (as opposed to optical fiber) 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 system - most data network specifies 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.

Type 1 and 1A, meanwhile, are special-purpose four-conductor cables designed for particular computer network protocols.  They have never achieve widespread acceptance.


Just as speed has made Cat 5 the de facto standard for data networks, it has driven manufacturers to develop and market "extended performance" Cat 5 cables.  These cables - which are manufactured with tighter twisted, more precise conductor-to-conductor spacing, and premium insulation - are rated at 350 MHz.  But because there are no extended performance Cat 5 outlets and patch panels to connect to these premium cables, there are no guarantees the resulting system can perform at that rating.

1  EIA/TIA-568A, the Commercial Building Telecommunications Cabling Standard, is the fundamental standard for telecom/LAN wiring.  It defines the basic cable and outlet performance categories (Cat 3, 4, and 5 copper, plus optical fibers) as well as "horizontal" and "backbone" cabling.  In addition, this standard requires teledata wiring to be installed in a star or radial configuration, with homeruns from every outlet.