25pair

25-pair, or 25-pair cable, is a type of telecommunications cable that contains 25 twisted copper pairs inside a single outer sheath, totaling 50 conductors. It was widely used for analog voice circuits and early data links, particularly in office buildings, central offices, and distribution frames, where many lines needed to be routed over a single run. The format supported multi-line connections and cross-connecting between equipment.

Construction and identification: Each pair is two insulated copper conductors. Pairs are identified by the established 25-pair color code, a system of solid and striped colors that lets technicians label and trace specific circuits. Cables can be jelly-filled for moisture resistance or dry-core, and may include shielding or armor for specific installation environments such as risers or outdoors.

Applications and current status: While most new networks have moved to fiber or higher-density copper solutions and to Ethernet-based delivery, 25-pair cables remain in service in many older buildings and legacy telephone systems. They are often encountered in cross-connect blocks, patch panels, and trunks that still terminate multiple voice lines or analog services. Proper documentation of pair assignments and careful testing are important due to the large number of pairs in a single jacket.

See also: Twisted pair cables, telephone distribution cable, 50-pair cables.