Telephone exchange system employing means capable of breaking a connection between a terminal unit and a switch frame using mechanical latching type crossbar switches

In a telephone exchange system including a switch frame having a plurality of input terminals and a plurality of output terminals, between which terminals selectively interconnectable stage of mechanical latching type crossbar switches are coupled;

• an incoming terminal unit having its input coupled to an external end device and its output coupled to one of said input terminals of said switch frame;
• an outgoing terminal unit having its input coupled to one of said output terminals of said switch frame;
• and
• a common control for controlling the establishment of a channel through the crossbar switches from the input to output terminals thereof and for setting up a call connection circuit from the external end device, through the incoming terminal unit and the channel, to said outgoing terminal unit;
• the improvement wherein said outgoing terminal unit comprises:
• first disconnecting means, responsive to the opening of the call connection circuit at the external end device, for electrically disconnecting the input of said outgoing terminal unit with the output terminal of said switch frame;
• and
• said incoming terminal unit comprises
• second disconnecting means, responsive to the disconnecting of the call connection at the outgoing terminal unit by the first disconnecting means, for electrically disconnecting the output of said incoming terminal unit with the input terminal of said switch frame.