CAT5 & 5e CABLES
Category 5 cable
is a twisted pair high signal integrity cable type often referred to as
Cat5 or Cat-5. Most Category-5 cables are unshielded, relying on the
twisted pair design for noise rejection. Category 5 has been superseded
by the Category 5e specification. This type of cable is used in
structured cabling for computer networks such as Ethernet and ATM, and is also used to carry many other signals such as telephony and video.
Category 5 cable includes 4 twisted
pairs in a single cable jacket. This use of balanced lines helps
preserve a high signal-to-noise ratio despite interference from both
external sources and other pairs (this latter form of interference is
called crosstalk). It is most commonly used for 100 Mbit/s networks,
such as 100BASE-TX Ethernet, although IEEE 802.3ab defines standards for
1000BASE-T – Gigabit Ethernet over category 5 cable. Each of the four
pairs in a Cat5 cable has differing precise number of twists per meter
based on prime numbers to minimize crosstalk between the pairs. On
average there are 6 twists per 5 centimeters.
CAT5 Cable Standard
The specification for Category 5 cable
was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These
documents specified performance characteristics and test requirements
for frequencies of up to 100 MHz.
United States T568B Wiring
Connectors and other information
The cable exists in both stranded and solid conductor forms. The
stranded form is more flexible and withstands more bending without
breaking and is suited for reliable connections with insulation piercing
connectors, but makes unreliable connections in insulation-displacement
connectors. The solid form is less expensive and makes reliable
connections into insulation displacement connectors, but makes
unreliable connections in insulation piercing connectors. Taking these
things into account, building wiring (for example, the wiring inside the
wall that connects a wall socket to a central patch panel) is solid
core, while patch cables (for example, the movable cable that plugs into
the wall socket on one end and a computer on the other) are stranded.
Outer insulation is typically PVC or LSOH.
Cable types, connector types and cabling topologies are defined by
TIA/EIA-568-B. Nearly always, 8P8C modular connectors, often incorrectly
referred to as "RJ-45", are used for connecting category 5 cable. The
specific category of cable in use can be identified by the printing on
the side of the cable.
The cable is terminated in either the T568A scheme or the T568B
scheme. Canada and Australia use the T568A standard, and the United
States commonly uses T568B scheme. It really doesn't make any difference
which is used as long as you use only one of the standards so all
connections are the same at your location to avoid confusion and
potential problems. Mixed cable types should not be connected in series
as the impedance per pair differs slightly and may cause signal
degradation. The article Ethernet over twisted pair describes how the
cable is used for Ethernet, including special "cross over" cables.
10BASE-T (IEEE) and 100BASE-TX (IEEE) Ethernet connections require
two cable pairs. 1000BASE-T (IEEE) and 1000BASE-TX (TIA/EIA-854,
requiring category 6 cabling) Ethernet connections require four cable
pairs. Four pair cable is by far the most commonly available type.
Most Cat5 cables can be bent at a radius approximately 4 times the diameter of the cable.
Maximum Cable Segment Length
According to the ANSI/TIA/EIA standard for category 5e cable,
(TIA/EIA 568-5-A) the maximum length for a cable segment is 100
meters (328 ft). If longer runs are required, the use of active hardware
such as a repeater, or a switch, is necessary. This 100 meter limit is
all inclusive. According to the standard, the practical limit for
permanently installed cable is about 90 meters, leaving 5 meters at each
end for the CAT5 patch cables that connect the end equipment to the wall panel.