Patent ID: 7075195

Claim:
In a system including an alternating current electrical power source and an electrically-operated machine, said electrical power source having first and second power supply terminals, and said machine having at least one electrical load, first and second power supply inputs that are operably coupled to said first and second power supply terminals, and a first switching device operably disposed between one of said first and second power supply inputs and said at least one electrical load, said first switching device manually-operated between one of an ON state and OFF state, wherein in said ON state electrical power supplied to said first and second power supply inputs passes through said first switching device for powering said at least one electrical load, and wherein in said OFF state electrical power supplied to said first and second power supply inputs does not pass through said first switching device such that power is not provided to said at least one electrical load, an apparatus for controlling supply of electrical power provided by said electrical power source to said machine, the apparatus comprising: a second switching device operably coupled between a given one of said first and second power supply inputs and a corresponding one of said first and second power supply terminals of said electrical power source, said second switching device having a control node for selectively controlling said second switching device into one of a conducting-state and non-conducting state in response to control signals supplied thereto; and a plurality of circuit elements, operably coupled to said control node of said second switching device, that generate a control signal that operates said second switching device in said non-conducting state when i) said electrical power source removes and subsequently supplies electrical power to said first and second power supply terminals and ii) said first switching device is manually-operated in said ON state concurrent with said electrical power source subsequently supplying electrical power to said first and second power supply terminals, to thereby isolate said machine from said electrical power source and prevent hazardous turn-on of said machine; wherein said plurality of circuit elements comprise a switchable current path leading to said control node of said second switching device said switchable current path being selectively turned OFF and ON in accordance with state of said first switching device, and said switchable current path including a current path through at least one transistor whose control electrode is electrically connected to a shunt current path leading to said first switching device.