Most residences are wired with the full four-wire cable, but many only have the inner pair actually connected to anything, LocalTalk was designed to use only the outer pair (the black and yellow wires). Many homes also used the second pair for power, with a transformer wired into an outlet near one jack providing 24 or so volts DC to all phones in the house. Technically these would be RJ11, because there is still only one telephone line connected, although RJ14 cords are required to access whatever is on the second pair. These connectors are sometimes also wired for RS-232 serial communication used on certain devices.