External current protecting system

Abstract

Abstract PURPOSE:To protect a subscriber line against an external current impressed continuously by providing a detecting circuit of an external current on the subscriber line, and opening a channel by an output of a timing circuit for discriminating a fact that a detecting output exists for a prescribed time. CONSTITUTION:An external current detecting circuit 23 is provided on a subscriber's circuit 2 of a telephone exchange, and the circuit 23 detects an external current impressed between a line A and a line B, and between the line A or the line B and the ground by a detecting circuit of a high impedance. A timing circuit 24 discriminates a fact that a detecting output of the circuit 23 has been continued exceeding a prescribed time, and drives a relay C only in case said output has been continued, for instance, about two seconds or more. The relay C cuts off a line wire side channel and a current supplying circuit, and a channel of a supervisory circuit 22 side. In this way, it is possible to prevent a breakdown of a subscriber's circuit caused by an external current impressed continuously to the channel.

Inventors

• 👤 Keiichi Ueda
• 👤 敬一 植田

Bibliographic Details