Instruments for checking the operation of earth leakage circuit breakers

Claim 1

An instrument for checking the operation of an earth leakage circuit breaker, said earth leakage circuit breaker being incorporated in a three wire a.c. circuit presenting live, neutral, and earth output lines for connection of loads thereto and detecting a predetermined leakage current between the live and earth lines in said a.c. circuit, and then automatically breaking the circuit when a predetermined leakage current exists, said checking instrument comprising in combination a terminal for connection to each line in said a.c. circuit such that the instrument constitutes a load, a first capacitor, means including a rectifier coupling said first capacitor across said terminals for connection to the live and neutral lines, said first capacitor thereby being charged through said rectifier when the instrument is connected to said a.c. circuit to provide a power source, a test switch connected in series with an impedance across said terminals for connection to the live and earth lines, said test switch when closed providing a shunt circuit path between said live and earth terminals simulating a predetermined live line to earth line leakage current, a second capacitor connected in circuit with said test switch between said terminals for connection to the live and neutral lines of the a.c. circuit, such that said second capacitor charges only when said test switch is closed, whereby said earth leakage circuit breaker being tested serves upon proper operation thereof to break the a.c. circuit whereupon said second capacitor ceases to charge, said first capacitor thereafter continuing to provide a power source for the instrument after disconnection of the a c circuit, said instrument further including an amplifier powered by said first capacitor, and means coupling said second capacitor to the input of said amplifier, said amplifier operating warning means for indicating the state of charge of said second capacitor, which is a measure of satisfactory operation of the circuit breaker being tested.