Safety tester for electrical appliances and receptacles

Claim 1

A portable device for testing electrical characteristics of appliances having exposed metallic parts and three male prongs, said device comprising: a. a housing member, b. power source connecting means having two terminal leads, c. a bridge circuit contained in the housing member, said bridge circuit having a first bridge terminal for connecting a first and second bridge arm to one power source terminal lead, a second bridge terminal connecting a third bridge arm to said second bridge arm, a third bridge terminal connecting the third bridge arm to the other power source terminal lead, and a fourth bridge terminal terminating one end of said first bridge arm, said bridge circuit comprising: 1. electrical resistance means in said first, second and third bridge arms, 2. a controllable switching element connected between said first and fourth bridge terminals, said controllable switching element having a control terminal, 3. electrical indication means connected in series with said controllable switching element, 4. means for connecting the control terminal of the controllable switching element to said second bridge terminal, 5. said controllable switching element actuated when the voltage at said second bridge terminal is greater than the voltage at said fourth bridge terminal, 6. means for connecting male line prongs of the appliance under test to said second bridge terminal, 7. means for connecting a male ground prong of the appliance under test to the third bridge terminal, thereby controlling the voltage of said control terminal in response to low insulation resistance between said male line prongs and said male ground prong, and 8. probe means connected to said fourth bridge terminal for connection to said exposed metallic parts of said appliance under test for controlling the voltage at said fourth bridge terminal in response to the appliance ground resistance between said exposed metallic parts and said male ground prong, whereby said indication means is actuated only upon a satisfactory insulation resistance test and a ground continuity test.