Fault Sensing with an Artificial Reference Potential Provided by an Isolated Capacitance Effect

When an electric tool or appliance loses its safety ground connection (due to the ground pin being cut or due to the use of a three-to-two adapter), and an internal fault occurs, the metal housing may become electrically "hot" resulting in a safety hazard. This paper presents a grounding detector (GDT) circuit that could be used in conjunction with a ground fault circuit interrupter (GFCI). The advantage of the GDT over the GFCI is because the former monitors a voltage and the latter monitors a current. The GDT continuously monitors the voltage on the metal housing of the appliance. If the metal housing becomes electrically "hot", the GDT immediately detects this hazardous condition and takes corrective action, disconnecting the 120 Vac power from the hazardous appliance, and activating an alarm. A GFCI would take no corrective action until a human comes in physical contact with the hazardous appliance resulting in the flow of ground fault current. The authors have a United States patent on the GDT circuits