LEAKAGE DETECTOR FOR DETERMINING POSSIBLE SHOCK HAZARDS TO HUMANS

• US 3,784,903 A
• Filed: 11/10/1970
• Issued: 01/08/1974
• Est. Priority Date: 11/10/1970
• Status: Expired due to Term

• Current Assignee: RCA Corporation
• Original Assignee: Lucius Ponder Thomas
• Inventors: Thomas, Lucius Ponder
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/088,362
• Time in Patent Office: 1,155 Days
• Field of Search: 324/51,133,119,110,127,72.5
• US Class Current: 324/510
• CPC Class Codes: G01R 19/155 Indicating the presence of voltage
• CPC Class Codes: G01R 35/00 Testing or calibrating of apparatus covered by the other groups of this subclass
• CPC Class Codes: H01H 83/04 with testing means for indicating the ability of the switch or relay to function properly
• CPC Class Codes: H02H 5/12 responsive to undesired approach to, or touching of, live parts by living beings

Abstract

A full-wave rectifier bridge circuit is coupled to a current reading meter by a resistor approximating the body load resistance of a human being. The meter provides an '"'"''"'"''"'"''"'"'up scale'"'"''"'"''"'"''"'"' indication for electrical sources supplying alternating power or direct current powers of either polarity, and is useful in performing leakage current tests on electrical appliances.

Claims

1. A leakage detector for determining possible shock hazards to humans from exposed, accessible parts of electrically operating apparatus which are not normally intended to carry electrical voltages, comprising:

a full wave rectifier circuit having an input terminal, an output terminal, a reference terminal and an intermediate terminal;

first means for directly connecting the reference terminal of said rectifier circuit to a point of ground potential;

second means for adaptively contacting the input terminal of said rectifier circuit with various ones of said exposed parts in determining the presence thereat of any such unintended voltages;

a direct current milliammeter; and

a first resistor coupling one terminal of said milliammeter to the output terminal of said rectifier circuit, the intermediate terminal of which is direct current coupled to a second terminal of said milliammeter, and with said first resistor being of a resistance value approximating the body resistance of a human being;

whereby said direct current milliammeter provides an indication of the direct current which would be caused to flow through said resistor due to the presence of any unintended voltages on those exposed parts contacted by said second means, and an indication of the direct current which would pass through a human being who would come into physical contact with said energized parts unless measures were taken to correct such electrical leakages.

2. The electrical leakage detector of claim 1 wherein said rectiFier circuit includes a first semiconductor rectifier having an anode connected to said input terminal and a cathode connected to said output terminal, a second semiconductor rectifier having an anode connected to said reference terminal and a cathode connected to said output terminal, a third semiconductor rectifier having an anode connected to said intermediate terminal and a cathode connected to said input temrinal and a fourth semiconductor rectifier having an anode connected to said intermediate terminal and a cathode connected to said reference terminal.

3. The electrical leakage detector of claim 2 wherein a second resistor is additionally included to serially couple said milliammeter to said first resistor and wherein a semiconductor diode is also included coupled across said second resistor and said milliammeter to become conductive and limit current flow through said milliammeter when the current through said second resistor reaches a predetermined value.

4. The electrical leakage detector of claim 2 wherein a second resistor is additionally included to serially couple said milliammeter to said first resistor and wherein a silicon controlled rectifier is also included having input and output electrodes connected to a source of energizing potential and to an alarm means, respectively, and also having a control electrode coupled across said second resistor and said milliammeter to activate said alarm means when the voltage developed across said second resistor and said milliammeter in response to the current flowing through said first resistor reaches a predetermined value.