Cat 3, short for Category 3, is a UTP (Unshielded Twisted Pair) cable designed to carry voice and data up to 10 Mbps (mega bits per second), with possible transmission frequencies up to 16 MHz. Cat 3 cable is part of a family of copper cabling standards defined jointly by the Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA). If a cable is certified as Category 3 and not just twisted pair wire, then it will have "Cat 3" printed on the shielding.
Cat 3 and Cat 5 are the most widely installed categories of cable. Cat 3 cable comes with four pairs of twisted wires. Though both Cat 3 and Cat 5 cables may look similar, Category 3 is designed for a lower speed data transmission purpose and can cause transmission errors if it is used for faster speeds. Cat 3 is certified only for a 16 MHz signal while Category 5 cable can support a 100 MHz signal.
Ethernet 10Base-T runs over Cat 3 cable, but uses only two pairs of the available four pairs. Ethernet 100Base-T4 utilizes all 4 pairs (8 wires).
Most cables used for voice transmission are rated Cat 3.
In the early 1990s, Cat 3 cable was widely accepted as a standard cabling format among computer network administrators. But the Cat 3 cable standard was entirely replaced with the advent of Cat 5 cable standard, which offers higher data transmission speeds.
Today, Cat 3 cable is one of the oldest cable standards used for data transmission. However, Category 3 cable is very inexpensive and can provide outstanding communications for voice telephones lines in a PBX network.