Category 3 or Cat3 Cable is a UTP, or untwisted pair cable commonly used for phone system or voice communications cabling. Category 3 Cable The popularity of Cat3 cable as a cost effective means of deploying voice services remains robust since the majority of business telephones only require a single pair of wires to operate. Originally designed to carry data at up to speeds of 10Mbit/s, Cat3 has been replaced by Cat5e for higher data speed demands. Cat 3 Connectors Cat3 Cable is typically connected in jacks and telephones with RJ11 connectors as pictured here. At the phone system level, Cat3 is seperated and usually punched down on 66 blocks or 110 blocks for ease of integration into your voice network.