Abstract: To detect abnormality of a connecting section and appropriately disconnect the connecting section, the present invention refers to the result of detection by a state detection section configured to detect the state of each of a plurality of terminals to detect the presence or absence of abnormality of each of the plurality of terminals, In a case where abnormality has been detected, the present invention switches the direction of electric current flowing through an electromagnet. This disconnects a first connecting section and a second connecting section from each other.

Abstract: The system comprises at least one teleprinter station (1) connected to an exchange (3) by means of a transmission-reception line (2) and comprising a polarity detector (31) for the line circulating current, and a device (30) for reversing the connection of the line wires. If the wires erroneously become reversely connected following maintenance work on a line of single current type, then false call and conversation signals are generated which automatically trigger a checking operation in which the polarity detector is suitably examined under control of a ROM routine E controlling a CPU 84. If the current is found to be the reverse of the correct current, the reversing device is operated in order to reverse the polarity of the connection. In contrast, in the case of a double current line, the reversing device is operated when current is absent in the reception line, thus indicating an erroneous line connection. If the line current interruption is prolonged, a warning device (28) is activated.