What are Category 5 and Category 6 cables?

Cat 5 and Cat 6 Cables

  Cat 5 and Cat 6 cables refer to two specifications which have been created for Ethernet computer network cabling. The "cat" is actually a shortened version of "category." These cables replace earlier categories of cables, such as cat 3 cable, which were used for the same thing.


  Although the terms "Cat 5" and "Cat 6" actually refer to the specifications that were developed for these cables and to which the cables are manufactured, the cables themselves are commonly referred to by these names. These cables are typically terminated with an eight pin modular connector, similar to a telephone connector, but wider.


  Both cables consist of four twisted pairs of wires. There is no shielding, as these cables depend upon the twisted pair design and differential signaling to provide noise rejection. This combination works extremely well, as the probability of the same interference striking both wires in the twisted pair to the same degree is extremely low.


  The differential signal is passed over the wire, with one of the two signals inverted. With a digital signal, a positive noise spike would increase the voltage of the signal on one line and reduce it on the other line. At the other end, the signals are compared, and the noise spike cancels out.

differential signals

  Each twisted pair of wires is capable of carrying a separate signal, so the cable is capable of carrying four separate signals. Earlier 10BASE-T and 100BASE-TX Ethernet connections only required two cable pairs. However, 1000BASE-T Ethernet requires four cable pairs.


  The Cat 5 cable specification has been superseded by the Cat 5e specification (the "e" stands for "enhanced"). The difference between the two is that the Cat 5e specification tightens up the specification for crosstalk between pairs. This is accomplished by ensuring that the number of twists per meter is different for each pair.

Pair Color
Cm per turn

Turns per meter














  The difference between Cat 5e and Cat 6 cable is the wire gauge for the conductors used in the cable. Cat 5e cables typically use 24 to 26 gauge wire.  Cat 6 cables use 22 to 24 gauge wire. The gauge is dependent upon the cable length, as a longer cable requires a larger wire gauge to carry the same signal without appreciable signal loss. Cat 6 cables' larger wire size allows them to carry a faster signal without suffering any problems with signal loss.
While Cat 5 cables can carry 1000BASE-T Ethernet signals (Gigabit Ethernet), Cat 5 cables can carry 10GBASE-T Ethernet signals (10-Gigabit Ethernet).

Ethernet Communications Protocol

Common Name


Cable Required



10 Mbit/s

Cat 3


Fast Ethernet

100 Mbit/s

Cat 5


Gigabit Ethernet

1 Gbit/s (1000 Mbit/s)

Cat 5


10-Gigabit Ethernet

10 Gbit/s

Cat 6


  For lower bandwidth applications, Cat 6 cables can be used in place of Cat 5, as they are essentially the same cable, with the same type of connectors on the end. However, the connectors themselves are not interchangeable, as the crimp lugs in the connector need to be sized for the wire. The larger gauge wire in the Cat 6 cable will not fit into the Cat 5 modular connectors and the smaller gauge wires used in the Cat 5 cable will not make good mechanical and electrical contact in the Cat 6 modular connectors.


  The maximum length for which Cat 5 or Cat 6 cables is designed to be run is 100 meters (328 feet). For longer runs, it is recommended to use active hardware, such as a repeater, to amplify the signal. 


Cat 5 & Cat 6 Crossover Cables

  For most networks, the Cat 5 or Cat 6 cables are wired straight through. That means that the same wire colors are attached to the same pin numbers on both ends. There is a specific order in which these colors are connected, which we won't bother to go into here.

cat6 cable



  When computers are connected in a simple peer-to-peer network with only two computers and no hub, a standard Cat 5 or Cat 6 cable won't work. Both computers would be trying to send over the same wire at the same time. They would also both be trying to receive over the same wire at the same time. Neither computer can "hear" the other, because the output of one computer isn't connected to the input of the other computer.

  To solve this problem a Cat 5 or Cat 6 Crossover cable is used. These look the same as the regular cables, but the pins are wired opposite.  If you put the two connectors side-by-side, you can see the colors of the wires arranged opposite in the two connectors.  This type of cable connects the output of one computer to the input of the other, and vice-versa. Crossover cables will be so marked on their jacket.

Rich Murphy