Skjerven, Morrill, MacPherson, Franklin & Friel
Apparatus and methods for coupling a case of an electric appliance to an external ground and for detecting leakage current
 The apparatus for automatically coupling an internal ground of an electric appliance to an external ground, comprises first and second AC power lines for supplying an AC input to a load; a neutral ground generating circuit for combining the first and the second AC power lines to produce a neutral ground point; a first detection circuit for detecting a current flow from the first AC power line to the internal ground to generate a first current detection signal; a second detection circuit for detecting a current flow from the second AC power line to the internal ground to generate a second current detection signal; and a ground coupling circuit for connecting, in response to the second current detection signal, the first AC power line as the external ground to the internal ground; for connecting in response to the first current detection signal, the second AC power line as the external ground to the internal ground; and for connecting the neutral ground point as the external ground to the internal ground when the first and the second current detection signals are absent. 
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inventional inventional
Jung M.
Kim