Twisted pair is two insulated wires twisted together to reduce interference. The twists cancel out electromagnetic noise. It is the most common cable for telephone and Ethernet. It is cheap, flexible, and easy to install. It is also limited in bandwidth and distance.

Twisted pair comes in two main types. Unshielded twisted pair is common in offices and homes. Shielded twisted pair has a foil or braid around the pairs. It is used in noisy environments. Categories rate the cable: Cat 5e, Cat 6, Cat 6a, Cat 7. Higher categories support higher speeds.

Twisted pair categories

• Cat 3: telephone, 10 Mbps
• Cat 5e: Ethernet, 1 Gbps
• Cat 6: 1 Gbps to 10 Gbps, short runs
• Cat 6a: 10 Gbps, longer runs
• Cat 7: shielded, 10 Gbps+

Twisted pair is the workhorse of LANs. It connects computers, phones, and cameras. It carries power over Ethernet. It is being replaced by fiber for long runs and high speeds. But it is still the most common cable in buildings. The twisted pair is not going away soon.