Abstract: A switching circuit for use with an electrical appliance, and comprising first and second normally open switch terminals and a high sensitivity impedance measuring circuit coupled to the first and second switch terminals for measuring an impedance therebetween, and producing at an output thereof a switching signal if the impendance is lower than a predetermined threshold of 500 M&OHgr;. The appliance is coupled to the output of the impedance measuring circuit so as to be responsive to the switching signal. The circuit finds particular application for controlling and protecting electrical appliances operating from an a.c. electrical means supply, in which case one of the switch terminals is connected to a virtual ground connection which is electrically floating with respect to a ground feeder of an electrical mains supply.

Abstract: A protection device for use in conjunction with an electrical appliance having an electrically conductive outer casing and which protects against the casing becoming "live" regardless of the state of a ground connection (GND) associated with an electrical socket to which the appliance is connected. A virtual ground connection is electrically floating with respect to the ground connection (GND) of the electrical socket, and is electrically coupled to the casing of the electrical appliance instead of the ground connection of the electrical socket. A differential comparator circuit compares a fraction of the voltage between the live and neutral connections with a voltage at the virtual ground connection of the appliance, producing a fault signal if a difference between the two voltages exceeds a predetermined threshold.