Electrical grounding and insulation resistance tester

Claim 2

A tester, for testing electrical hand tools and the like of the type having a power connection plug which includes two power terminals and a grounding terminal, said tester comprising two electron discharge devices having control electrodes, an electric power source, one of said devices having a load circuit connected to said power source, a normally open circuit having two contacts adapted for connection respectively to the grounding terminal and to at least one of the power terminals of the plug of the tool or the like, said contacts being in a circuit from said source to said control electrode of said one of said devices for biasing said one device into conductive condition in response to insulation resistance of the tool or the like as measured between the grounding terminal and the one power terminal of less than a predetermined resistance, the control electrode of the other said device being connected to said load circuit of said one device and operative to bias said other device in conductive condition in response to non-conduction of said one device and in nonconductive condition in response to conduction of said one device, and a second load circuit for said other device connected to said source and comprising a current indicating means in series with contact means adapted for connecting to a conductive part oF the frame of the tool and said second load circuit further comprising in series said contact which is adapted for connection to the grounding terminal, said second load circuit being adapted to be completed by a continuous grounding circuit of the tool from its frame to the grounding terminal of its plug.

Claim 3

The combination according to claim 1 wherein said electric power source is a source of alternating current voltage.

Claim 4

An automatic insulation resistance and grounding tester for electrical equipment of the type having a connector plug with at least two power terminals and one grounding terminal, said tester comprising a first normally non-conductive rectifier having a control electrode, means for supplying a positive voltage to said control electrode comprising contact means adapted to be connected in series with the grounding terminal and at least one of the power terminals of the plug of the equipment to be tested, said rectifier being biased for conduction when the insulation resistance of the equipment to be tested is low, a first load circuit for said first rectifier, a second normally conductive rectifier having a control electrode, a respective second load circuit for said second rectifier, said control electrode for said second rectifier being connected to said first load circuit and responsive to conductance of said first rectifier to be biased to a cut off voltage of said second rectifier, said second load circuit comprising current indicating means connected in series with a test terminal adapted to be in electrical contact with a portion of the equipment to be tested for proper connection to the grounding terminal of the plug thereof, and with said contact means adapted to be connected to the grounding terminal of such plug, said indicating means indicating current flow in said second load circuit.

Claim 5

An automatic insulation resistance and grounding tester for electrical equipment of the type having a connector plug with at least two power terminals and one grounding terminal, said tester comprising a first normally non-conductive rectifier having a control electrode, means for supplying a positive voltage to said control electrode comprising contact means adapted to be connected in series with the grounding terminal and at least one of the power terminals of the plug of the equipment to be tested, said rectifier being biased for conduction when the insulation resistance of the equipment to be tested is low, a first load circuit for said first rectifier, a second normally conductive rectifier having a control electrode, a respective second load circuit for said second rectifier, said control electrode for said second rectifier being connected to said first load circuit and responsive to conductance of said first rectifier to be biased to a cut off voltage of said second rectifier, said second load circuit comprising current indicating means connected in series with a test terminal adapted to be in electrical contact with a portion of the equipment to be tested for proper connection to the grounding terminal of the plug thereof, and with said contact means adapted to be connected to the grounding terminal of such plug, said indicating means indicating current flow in said second load circuit.

Claim 6

An automatic insulation resistance and grounding tester for electrical equipment of the type having a connector plug with at least two power terminals and one grounding terminal, and such equipment having a conductive portion normally groundingly connected to such grounding terminal, said tester comprising a first normally non-conductive rectifier having a control electrode, circuit means including an open circuit adapted to be effectively closed by connection thereacross of the grounding terminal and a power terminal of the equipment plug when the insulation resistance of such tool is low and to remain effectively open when such insulation resistance is high, said circuit means being operative to supply a positive voltage to said control electrode to trigger conduction of said rectifier when said open circuit is effectively closed and being inoperative to trigger said rectifier when said open circuit is effectively open, whereby said rectifier conducts when such equipment having low insulation resistance is so connected, a first load circuit for said first rectifier, a second normally conductive rectifier having a control electrode, a respective second load circuit for said second rectifier, said control electrode for said second rectifier being connected to said first load circuit and responsive to conductance of said first rectifier to cut off said second rectifier, said second load circuit comprising indicating means connected in series with a test terminal adapted to be placed in electrical contact with such conductive portion of the equipment, and a second test terminal adapted to be placed in electrical contact with such grounding terminal of such plug of the equipment. said second load circuit being open between said test terminals in the absence of such electrical connections of such equipment.

Claim 7

An automatic insulation resistance and grounding tester for electrical equipment of the type having a connector plug with at least two power terminals and one grounding terminal, and such equipment having a conductive portion normally groundingly connected to such grounding terminal, said tester comprising a first normally non-conductive rectifier having a control electrode, circuit means including an open circuit adapted to be effectively closed by connection thereacross of the grounding terminal and a power terminal of the equipment plug when the insulation resistance of such tool is low and to remain effectively open when such insulation resistance is high, said circuit means being operative to supply a positive voltage to said control electrode to trigger conduction of said rectifier when said open circuit is effectively closed and being inoperative to trigger said rectifier when said open circuit is effectively open, whereby said rectifier conducts when such equipment having low insulation resistance is so connected, a first load circuit for said first rectifier, a second normally conductive rectifier having a control electrode, a respective second load circuit for said second rectifier, said control electrode for said second rectifier being connected to said first load circuit and responsive to conductance of said first rectifier to cut off said second rectifier, said second load circuit comprising indicating means connected in series with a test terminal adapted to be placed in electrical contact with such conductive portion of the equipment, and a second test terminal adapted to be placed in electrical contact with such grounding terminal of such plug of the equipment. said second load circuit being open between said test terminals in the absence of such electrical connections of such equipment.

Claim 8

In a tester for electrical hand tools and the like having a power connection plug including two power connector terminals and a grounding terminal, the combination comprising a source of power, first circuit means connected to said source and including two test terminals and being operative between a first condition and a second condItion, said circuit means being responsive to resistance between said test terminals to be in said first condition when such resistance is less than a predetermined value and in said second condition when such resistance is greater than said predetermined value, second circuit means including switch means responsive to the condition of said first circuit means, said switch means being normally conductive in response to said second condition of said first circuit means, said second circuit means further including an electrically actuated indicating means responsive to conduction through said switch, and means adapted for connecting grounding portions of such hand tool or the like to be tested for continuity in series with said switch means across said source, said two test terminals being adapted to be connected respectively to the grounding terminal and to at least one of the power connector terminals of such hand tool or the like for testing the insulation resistance thereof, whereby said indicator is energized when the insulation resistance of such tool or the like between the grounding terminal and power connection terminal of its plug is higher than said predetermined value and when concurrently such continuity exists between such portions.

Claim 9

In a tester for electrical hand tools and the like having a power connection plug including two power connector terminals and a grounding terminal, the combination comprising a source of power, first circuit means connected to said source and including two test terminals and being operative between a first condition and a second condItion, said circuit means being responsive to resistance between said test terminals to be in said first condition when such resistance is less than a predetermined value and in said second condition when such resistance is greater than said predetermined value, second circuit means including switch means responsive to the condition of said first circuit means, said switch means being normally conductive in response to said second condition of said first circuit means, said second circuit means further including an electrically actuated indicating means responsive to conduction through said switch, and means adapted for connecting grounding portions of such hand tool or the like to be tested for continuity in series with said switch means across said source, said two test terminals being adapted to be connected respectively to the grounding terminal and to at least one of the power connector terminals of such hand tool or the like for testing the insulation resistance thereof, whereby said indicator is energized when the insulation resistance of such tool or the like between the grounding terminal and power connection terminal of its plug is higher than said predetermined value and when concurrently such continuity exists between such portions.

Claim 10

In a safety tester for an electrical tool having a power connection plug including two power terminals and a grounding terminal and such tool further including a frame portion and a normally continuous grounding connection between such frame portion and such grounding terminal, the combination of, a first bus and a second bus, power means for causing said first bus to be electrically positive with respect to said second bus, a first and a second electron discharge device each having a respective anode, cathode and control electrode, a first anode-cathode load circuit for said first device between said buses in which the cathode of the device is oriented toward said second bus and the anode is oriented toward said first bus, means adapted to connect the control electrode of said first device to said first bus through the insulation resistance of the tool between such grounding terminal and power terminals thereof for applying when said first bus is positive a positive triggering voltage to said control electrode in response to said insulation resistance being less than a predetermined value, a second load circuit for said second device between said buses in which the cathode of the device is oriented toward said second bus and the anode is oriented toward said first bus, said second load circuit including an electrical indicator device in series therein, the control electrode of said second device being connected to said first load circuit and responsive to conductance of said first device to apply to said control electrode of said second device a voltage less positive than the voltage required to trigger said device, said second load circuit having an open circuit portion in series therein adapted to be closed by connection of the grounding terminal and such frame portion of the tool across such open circuit portion thereby to close said second load circuit when such grounding connection of the tool is continuous.

Claim 11

In a safety tester for an electrical tool having a power connection plug including two power terminals and a grounding terminal and such tool further including a frame portion and a normally continuous grounding connection between such frame portion and such grounding terminal, the combination of, a first bus and a second bus, power means for causing said first bus to be electrically positive with respect to said second bus, a first and a second electron discharge device each having a respective anode, cathode and control electrode, a first anode-cathode load circuit for said first device between said buses in which the cathode of the device is oriented toward said second bus and the anode is oriented toward said first bus, means adapted to connect the control electrode of said first device to said first bus through the insulation resistance of the tool between such grounding terminal and power terminals thereof for applying when said first bus is positive a positive triggering voltage to said control electrode in response to said insulation resistance being less than a predetermined value, a second load circuit for said second device between said buses in which the cathode of the device is oriented toward said second bus and the anode is oriented toward said first bus, said second load circuit including an electrical indicator device in series therein, the control electrode of said second device being connected to said first load circuit and responsive to conductance of said first device to apply to said control electrode of said second device a voltage less positive than the voltage required to trigger said device, said second load circuit having an open circuit portion in series therein adapted to be closed by connection of the grounding terminal and such frame portion of the tool across such open circuit portion thereby to close said second load circuit when such grounding connection of the tool is continuous.

Claim 12

The combination according to claim 6 wherein said open circuit portion adapted to be closed by such grounding connection from such frame portion to such grounding terminal of the tool is common to said load circuits.

Claim 13

The combination according to claim 7 wherein said control electrode of said second device is provided with a positive voltage sufficient to trigger said second device in response to non-conduction of said first device.

Claim 14

The combination according to claim 6 wherein said first load circuit is complete between said buses in the absence of the tool, and wherein said control electrode of said second device is provided with a positive triggering voltage from said first load circuit in response to non-conduction of said first device.

Claim 15

The combination according to claim 6 wherein said power means provides alternating current voltage to said buses whereby said first bus is intermittently positive with respect to said second bus.

Claim 16

The combination according to claim 8 wherein said power means provides alternating current voltage to said buses whereby said second device is triggered into conduction in response to non-conduction of said first device during the half cycles in which said first bus is positive with respect to said second bus.

Claim 17

In a tester for an electrical tool or the like having a connector plug with at least two power terminals and a grounding terminal, the combination of a first electron discharge device having a control electrode, an opening biasing circuit to said control electrode adapted to be closed by the connection thereinto of the grounding terminal and a power terminal of the plug of a tool to be tested when the insulation resistance of the tool is less than a predetermined resistance and operative when so closed to bias said device for conduction, said first device being provided with a load circuit, a second electron discharge device including a respective control electrode connected to said load circuit of said first device and being biased by a voltage on said load circuit for conduction in response to non-conduction of said first device, an open load circuit for said second device adapted to be closed by the connection thereinto of the grounding terminal of the plug and the frame of the tool to be tested when the grounding connection between the frame and grounding terminal of the plug of the tool is continuous, and means for indicating the flow of current in said load circuit of said second device.

Claim 18

In a tester for an electrical tool or the like having a connector plug with at least two power terminals and a grounding terminal, the combination of a first electron discharge device having a control electrode, an opening biasing circuit to said control electrode adapted to be closed by the connection thereinto of the grounding terminal and a power terminal of the plug of a tool to be tested when the insulation resistance of the tool is less than a predetermined resistance and operative when so closed to bias said device for conduction, said first device being provided with a load circuit, a second electron discharge device including a respective control electrode connected to said load circuit of said first device and being biased by a voltage on said load circuit for conduction in response to non-conduction of said first device, an open load circuit for said second device adapted to be closed by the connection thereinto of the grounding terminal of the plug and the frame of the tool to be tested when the grounding connection between the frame and grounding terminal of the plug of the tool is continuous, and means for indicating the flow of current in said load circuit of said second device.