High sensitivity electrical switching circuit

摘要: A switching circuit for use with an electrical appliance (29), and comprising first (51a) second (51b) normally open switch terminals a high sensitivity impedance measuring coupled to the therebetween, producing at output thereof signal if is lower than predetermined threshold of 500 MΦ. The so as be responsive signal. invention finds particular application controlling protecting appliances operating from a.c. mains supply. For such applications, one connected virtual ground connection (46) which electrically floating respect feeder (41) In event contact between other contact, apparent fault produced. gives raise small current detected by produce may then used operate suitable relay appliance.