Telephone subscriber pair monitoring circuit - is mounted in subscriber's junction box and disconnects subscribers' appts. from protection against high voltage or current

摘要

The unit monitors the line between the telephone exchange and the subscriber's appts. Similar circuits are used in each line. When an unacceptable current or voltage is detected on either line, the subscriber's appts. is disconnected and an electronic switch switches in a characteristic termination impedance across the exchange line connections. Each circuit consists of a voltage detector, current detector, protection device and an electronic circuit breaker. The protection device can be a resistance and Zener diode or a spark-gap in parallel. The impedance switch can be operated by either current detector.