Abstract: A step-up transformer is disposed on a wiring substrate 51 on which an inverter which converts a commercial a.c. power into a high frequency power and a ground fault detection circuit are mounted and within a casing 52. Lead wires 53, 54 which extend from the opposite ends of the secondary winding of the step-up transformer to the outside thereof are mounted upright on the wiring substrate 51. Coils 57, 58 are disposed on air-core bobbins 55, 56, which are threaded by the lead wires 53, 54. Outputs from the coils 57, 58 are fed to a ground fault detection circuit.

Abstract: A step-up transformer is disposed on a wiring substrate 51 on which an inverter which converts a commercial a.c. power into a high frequency power and a ground fault detection circuit are mounted and within a casing 52. Lead wires 53, 54 which extend from the opposite ends of the secondary winding of the step-up transformer to the outside thereof are mounted upright on the wiring substrate 51. Coils 57, 58 are disposed on air-core bobbins 55, 56, which are threaded by the lead wires 53, 54. Outputs from the coils 57, 58 are fed to a ground fault detection circuit.

Abstract: Induced voltages of two tertiary coils magnetically coupled with two secondary coils, respectively, are detected separately by two voltage detector circuits, and the detected voltages V1 and V2 are compared by two comparators with a reference voltage VS. When wiring connected to either one of the two secondary coils or a neon tube is grounded, the induced voltage of the corresponding tertiary coil decreases, then the output from the corresponding comparator is reduced down to zero volt, then a light emitting element emits light, and a phototriac is turned ON to actuate a relay to turn OFF its contact switch, shutting off the supply of AC power.