Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1994-11-04
1996-08-20
DeBoer, Todd
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 48, 361113, H02H 316
Patent
active
055484662
ABSTRACT:
The present invention is directed to a system for sensing fault current flowing through a person who touches an exposed conductor in a cable connecting a machine to a power distribution center wherein the power distribution center has a number of power cables for connecting a number of machines thereto. Each power cable has a different frequency impressed thereon by an oscillator which frequency is transmitted through an electrical path including the power center if the operator touches the fault. A sensing circuit for each cable is connected in the electrical path and tuned to only the frequency applied to that cable. When the sensing circuit detects that frequency, the sensing circuit interrupts power to the cable. If, for some reason, the sensing circuit fails to interrupt power to the cable, within a selected time interval of less than one-half second, a backup system interrupts power to the entire power center. In order to detect ground faults, the ground conductor in each cable is grounded to the power center's frame through a zener diode bank which is in parallel with a high pass capacitor connected thereto by a preventive resistor. The zener diode bank also suppresses intermachine arcing should two machines touch or come into close proximity. In addition to ground faults, broken ground wires are detected by connecting each ground wire through a preventive resistor to a signal monitor. If a ground wire breaks, the signal monitor for that cable alerts the sensing circuit for that cable, and the sensing circuit interrupts power to the cable.
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