Abstract: A line identifier at a telecommunication switchboard comprises a matrix of magnetic-induction elements serving as current sensors for detecting a request for establishing a connection between a selected incoming line and a selected outgoing line. The sensors are connected to a multiplexer for providing samples in a time-division mode to a logic circuit controlled by a pair of microprogrammers and addressing a read/write memory for storing information on the states of the sensors. The logic network, upon receiving from a sensor an identification request for a selected outgoing line, such request implicitly coding a selected input line, activates a relay which closes a circuit enabling the energization of a sensor whose output signal to the logic network identifies the outgoing line selected via the switchboard for connection to the prior-identified incoming line.