Tip and Ring

Tip And Ring

Tip and ring are the standard industry terms of the two wires or sides of a telephone line. They originate from the early days of telephone service when concentric plugs were used that had one wire connected to the plug tip and another to a ring on the shaft. When inserted into a socket, a telephone connector would first connect the grounded circuit side on the tip, followed by the active battery potential on the ring. In the UK, tip and ring are referred to as the 'A' (earth) and 'B' (battery) wires.

Tip has a potential of 0 volts with respect to ground, while the battery side carries a DC potential of −48V when in the on-hook (idle) state (nominally −50 volts in the UK).