CATEGORY
5 CABLING
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.
GETTING EVER FASTER
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.
