Fuji Electric Co., Ltd.

Shoji Sasaki

Kiyoshi Tanigawa

Takashi Hashimoto

Katsumi Watanabe

The earth leakage breaker of the invention includes a first comparator; a second comparator connected to the first comparator; a third comparator having a threshold higher than the threshold of the first comparator for distinguishing a leakage current from the grounding current caused by a lightning surge or by the heavy ground fault; a monostable multivibrator triggered by the output of the third comparator for forming a time gate of a predetermined period; a counter for detecting a pulse outputted from the first comparator to distinguish whether the grounding current is caused by the lightning surge or by the heavy ground fault; and a trip signal generator circuit for outputting a trip signal in the case of leakage and heavy ground fault. The earth leakage breaker facilitates avoiding unnecessary breaking of the impulsive grounding current caused by the lightning surge.

Earth leakage breaker

In the particular embodiment of the invention described in the specification, a variable resistor is connected in potentiometer fashion to a DC power source and a time interval is selected according to the position of the movable contact. The ratio of the partial voltage provided by the movable contact to the full voltage applied to the resistor is determined and an oscillator signal target count for the selected time interval is computed from a count corresponding to the total voltage. The arrangement permits accurate time interval determination which is independent of variations in the supply voltage, variations in resistance value of the variable resistor, or environmental changes.

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Tochigi, Japan

Shoji Sasaki