Party line apparatus

Privacy and selective ringing in a two-party line system are implemented by using unidirectional diodes in the speech circuit and the ringer circuit, respectively, of the subscriber instruments. The diodes in the first subscriber instrument are oppositely poled with respect to those in the second subscriber instrument. Current sensors, in response to the application of a DC biased AC monitoring signal, provide party identification by sensing the direction of current flow in the line. Line terminal apparatuses are then switched onto the line, in response to the party identification current sensors, to provide the correct line polarity for the identified party.