Current sensing alarm arrangement for monitoring the presence of high voltage

Claim 1

An arrangement for detecting if an electrically conductive apparatus, structural member or the like may be inadvertently electrically connected to a source of high voltage, said arrangement comprising: (a) means including a continuous electrically conductive ground cable defining an electrical ground path from said apparatus, structural member or the like to a grounding point, said ground path defining means being sufficiently conductive to reduce to at most a negligible level any high voltage to which the apparatus, structural member or the like may be subjected; and (b) means for monitoring the current through said ground path and for indicating if the current level so monitored reaches a predetermined threshold level sufficiently high to indicate that the apparatus, structural member or the like is in electrical engagement with a source of high voltage, said monitoring means including means for directly sensing the current in said ground path and for producing a corresponding electrical signal, and means for comparing the magnitude of said signal to a reference signal serving as said threshold level, said current sensing means including transformer means which utilizes a section of said ground cable as a primary and which includes a secondary, whereby current carried by said ground cable is induced in and sensed by said secondary to produce said corresponding signal, said monitoring means including means for directly sensing the current in said ground path and for producing a corresponding electrical signal, means for comparing the magnitude of said corresponding signal to a reference signal serving as said threshold level, means for producing an alarm driving signal in the event that a current exceeding said threshold level is sensed, and an alarm responsive to said alarm signal for producing an audible and/or visual signal, said arrangement also including means for testing said monitoring means, said testing means including means for producing an oscillating signal, a transformer secondary forming part of said transformer means for simulating a fault current on said electrically conductive cable by means of induction through said transformer, whereby said simulated current is sensed by said first mentioned secondary forming part of said transformer means.