Category 3 cable

Category 3 cable, commonly known as Cat 3, is an unshielded twisted pair (UTP) cable designed to reliably carry data up to 10 Mbit/s, with a possible bandwidth of 16 MHz. It is part of a family of copper cabling standards defined jointly by the Electronic Industries Alliance and the Telecommunications Industry Association.

Category 3 was a popular cabling format among computer network administrators in the early 1990s, but fell out of popularity in favor of the very similar, but higher performing, Cat 5 standard. Presently, most new structured cable installations are built with Cat 5e or Cat 6 cable. Cat 3 is currently still in use in two-line telephone systems, and can easily be adapted to run VoIP (as long as you create a dedicated LAN for your VoIP telephone sets). While Cat 5 or higher is often recommended for VoIP, the reality is that the 10 Mbit/s bandwidth a cat 3 network can provide is far more than the 0.08 Mbit/s a VoIP phone needs at full load, and Cat 3 is even compatible with 802.3af PoE.

Note that unlike Cat 1, 2, 4, and 5 cables, Cat 3 is still recognized by TIA/EIA-568-B, its defining standard.

The newer 100BASE-T4 standard, which achieves speeds of 100 Mbit/s by using all 4 pairs of wires, allowed older Cat 3 based infrastructures to achieve a much higher bandwidth.

Advantages over Category 5 cable

Category 3 cable is available in up to 25 pairs, while category 5 cable is only available in 4 pairs. In homes and small offices, 100 megabit transmission is sufficient. The popular 100base-T standard works reliably up to 75m over 2 cat 3 pairs, while Marvell's new 100c3 standard works reliably up to 150m over just 1 cat 3 pair. Category 3 is therefore sufficient at this speed and offers more links per cable, greatly reducing the number of cables needed. When retrofitting homes with existing walls and no conduits this is a huge advantage.