Ground fault circuit interrupter for coaxial drop cable and method of operation

Abstract

A protective system for reducing the possibility of injury to individuals or damage to electrical equipment due to a fault in a coaxial drop cable connected between a tap unit receiving both RF signals and AC power from a main distribution line and a premise unit coupling the RF signals to RF receiving equipment and the AC power to other AC powered equipment at user premises. The tap unit includes a circuit having a first line connected at spaced points to an inner conductor with the RF signals flowing through the inner conductor and the AC power flowing through the first line. A regulated monitoring current flows from an AC to DC converter in the first line to a difference amplifier having a pair of inputs with a resistor connected between the two, whereby the difference amplifier serves to monitor the monitoring current by measuring the voltage drop across the resistor. A comparator receives the output of the difference amplifier and actuates an AC switch to selectively pass or block AC power in accordance with values of the monitoring current falling within or outside predetermined limits indicative of no-fault and fault conditions of the cable. A circuit in the premise unit electrically isolates the premises equipment from the monitoring current and includes a second resistor which is used to set the limits of the monitoring current