Category 4 (CAT-4) is a UL designation for unshielded twisted pair (UTP) data-grade cable, primarily used for voice and data transmission in commercial networks. It is also referred to as Level 4 cabling.
Category 4 cabling was designed to meet the demand for higher data transmission speeds in commercial and enterprise environments during the late 1980s and early 1990s. Built with four pairs of unshielded twisted copper conductors, CAT-4 could support frequencies up to 20 MHz. This increased bandwidth allowed for both voice and moderate-speed data applications, including early Token Ring networks and pre-Fast Ethernet systems. Compared to Category 3, CAT-4 offered better noise suppression, reduced crosstalk, and improved signal integrity.
Despite its advancements, CAT-4’s lifespan was short due to the rapid emergence of Category 5 cabling, which could support 100 Mbps transmission speeds and became the dominant standard for Ethernet. Although obsolete in modern networks, CAT-4 remains historically significant as an intermediate step in the evolution of structured cabling and data communication standards.
Category 4 cabling was classified by Underwriters Laboratories (UL) and recognized in early standards published by the Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA). These organizations helped establish standardized performance requirements and testing procedures for structured cabling systems.
Introduced as a successor to Category 3, Category 4 cabling gained popularity with the expansion of Token Ring networks in the early 1990s. Its ability to handle 16 Mbps made it suitable for data communication and voice applications. However, with the release of Category 5 cabling, offering significantly higher bandwidth, CAT-4 was quickly rendered obsolete. It remains an important milestone in the rapid development of networking technology during that era.