Leakage current detection and interruption circuit with improved shield

• US 20070159740A1
• Filed: 07/07/2006
• Published: 07/12/2007
• Est. Priority Date: 01/04/2005
• Status: Active Grant

• Current Assignee: Technology Research Group LLC (Southwire Company)
• Original Assignee: Technology Research Corporation (Southwire Company)
• Inventors: Brugner, Frank, Gandolfi, Paul, Williams, Thomas
• Granted Patent: US 7,623,329 B2
• Time in Patent Office: Days
• US Class Current: 361/42
• CPC Class Codes: H01H 73/44 reset by push-button, pull-knob or slide
• CPC Class Codes: H01H 83/02 operated by earth fault currents H01H83/14 takes precedence
• CPC Class Codes: H02H 1/0038 concerning the connection of the detecting means, e.g. for reducing their number
• CPC Class Codes: H02H 1/0069 by means of light or heat rays
• CPC Class Codes: H02H 3/044 Checking correct functioning of protective arrangements, e.g. by simulating a fault for differential current circuit breakers H02H3/335
• CPC Class Codes: H02H 3/16 responsive to fault current to earth, frame or mass with balanced or differential arrangement H02H3/26 ; monitoring earth connection H02H5/105
• CPC Class Codes: H02H 3/33 using summation current transformers H02H3/347 takes precedence

Abstract

A circuit is disclosed for disconnecting a power source upon the detection of a leakage current comprising a power cable having an insulated first and a second wire. The power cable has a conductive shield surrounding the first and second wires with a drain wire electrically contacting the conductive shield. A disconnect switch is interposed between the power source and the power cable. A primary circuit controls the disconnect switch. A secondary circuit is connected to the drain wire for sensing a leakage current between the conductive shield and one of the first and second wires. An optical switch interconnects the primary circuit and the secondary circuit for opening the disconnect switch upon the secondary circuit sensing a leakage current.

Claims

1. A circuit for disconnecting a power source upon the detection of a leakage current, comprising:

a power cable comprising an insulated first wire and an insulated second wire;

said power cable having a conductive shield surrounding said insulated first wire and said insulated second wire;

a drain wire having a first and a second portion;

said first portion of said drain wire being non-insulated and in contact with said conductive shield;

an outer insulating layer molded about said conductive shield;

a disconnect switch interposed between the power source and said power cable;

a primary circuit for controlling said disconnect switch;

a secondary circuit connected to said drain wire for sensing a leakage current between said conductive shield and one of said insulated first wire and said insulated second wire; and

an optical switch interconnecting said primary circuit and said secondary circuit for opening said disconnect switch upon said secondary circuit sensing a leakage current.

2. A circuit for disconnecting a power source as set forth in claim 1, wherein said conductive shield is a metallic foil.

3. A circuit for disconnecting a power source as set forth in claim 1, wherein said conductive shield comprises a metallic mesh.

4. A circuit for disconnecting a power source as set forth in claim 1, wherein said conductive shield comprises a polymeric material with a metallic conductive coating.

5. A circuit for disconnecting a power source as set forth in claim 1, wherein said conductive shield comprises a organic conductive polymeric material.

6. A circuit for disconnecting a power source as set forth in claim 1, wherein said first portion of said drain wire extends along substantially the total length of said conductive shield.

7. A circuit for disconnecting a power source as set forth in claim 1, wherein said drain wire is located internal to said conductive shield.

8. A circuit for disconnecting a power source as set forth in claim 1, wherein said drain wire is located external to said conductive shield.

9. A circuit for disconnecting a power source as set forth in claim 1, wherein said outer insulating layer establishes a mechanical engagement between said first portion of said drain wire and said conductive shield to provide an electrical connection between said drain wire and said conductive shield.

10. A circuit for disconnecting a power source as set forth in claim 1, wherein said outer insulating layer establishes a resilient mechanical engagement between said first portion of said drain wire and said conductive shield to provide an electrical connection between said drain wire and said conductive shield.

11. A circuit for disconnecting a power source as set forth in claim 1, including a housing having a line lug and a neutral lug for insertion within a line socket and a neutral socket and said ground socket of the power source;

and

said disconnect switch and said secondary circuit and said disconnect switch driver being located with in said housing.

12. A circuit for disconnecting a power source as set forth in claim 1, including a housing molded from a polymeric material;

a line lug and a neutral lug extending from said housing for insertion within a line socket and a neutral socket of the power source; and

said disconnect switch and said secondary circuit and said disconnect switch driver being located with in said housing.

13. A circuit for disconnecting a power source as set forth in claim 1, wherein said primary circuit includes a silicon controlled rectifier for opening said disconnect switch upon said secondary circuit sensing a leakage current from the wire.

14. A circuit for disconnecting a power source as set forth in claim 1, wherein said disconnect switch comprises a disconnect switch coil for changing said disconnect switch from a closed position connecting said power cable to the power source to an open position for disconnecting said power cable from the power source;

and

said primary circuit including a thyristor connected in series with said disconnect switch coil for changing said disconnect switch into said open position upon said secondary circuit sensing said leakage current to disconnect said power cable from the power source.

15. A circuit for disconnecting a power source as set forth in claim 1, wherein said secondary circuit includes a voltage divider circuit for powering said secondary circuit;

and

a light emitting device connected to said voltage divider circuit for sensing a leakage current.

16. A circuit for disconnecting a power source as set forth in claim 1, wherein said secondary circuit comprises a resistor for providing an intermediate voltage between voltage on said first wire and an insulated second wire;

and

said resistor connected to said second portion of said drain wire and a light emitting device for illuminating said light emitting device upon a leakage current in said conductive shield.

17. A circuit for disconnecting a power source as set forth in claim 1, wherein said secondary circuit comprises a voltage divider network having a voltage divider node;

and

said second portion of said drain wire connected in series with a light emitting device to said voltage divider node for illuminating said light emitting device upon a leakage current in said conductive shield.

18. A circuit for disconnecting a power source as set forth in claim 1, wherein said optical switch includes a light emitting device electrically connected to said secondary circuit for sensing a leakage current;

a photoconductive switch connected to said primary circuit for controlling said disconnect switch; and

said light emitting device being optically coupled to a photoconductive switch for electrically isolating said primary circuit from secondary circuit.

19. A circuit for disconnecting a power source as set forth in claim 1, wherein said optical switch includes an optocoupler switch having a light emitting device electrically connected to said secondary circuit for sensing a leakage current;

a photoconductive switch connected to said primary circuit for controlling said disconnect switch; and

said optocoupler switch having a light emitting device being optically coupled to a photoconductive switch for electrically isolating said primary circuit from secondary circuit.

20. A circuit for disconnecting a power source from a load, the power source having a line socket and a neutral socket, comprising:

a housing having a line lug and a neutral lug for insertion within said line socket and said neutral socket of the power source;

a power cable comprising an insulated first wire and an insulated second wire;

said power cable having a conductive shield surrounding said insulated first wire and said insulated second wire;

a drain wire having a non-insulated portion in contact with said conductive shield;

an outer insulating layer molded about said conductive shield;

disconnect switch located in said housing interconnecting said line lug and said neutral lug of said housing to said insulated first wire and said insulated second wire of said power cord;

a primary circuit for controlling said disconnect switch;

a secondary circuit connected to said drain wire for sensing a leakage current between said conductive shield and one of said insulated first wire and said insulated second wire; and

an optical switch interconnecting said primary circuit and said secondary circuit for opening said disconnect switch upon said secondary circuit sensing a leakage current to disconnect said power cord from the power source.

21. An circuit for disconnecting power from a power source, comprising a power cable comprising an insulated line wire, an insulated neutral wire, an insulated ground wire;

said power cable comprising a conductive shield surrounding said insulated line wire, said insulated neutral wire and said insulated ground wire;

a drain wire having a first and a second portion;

said first portion of said of said drain wire being non-insulated and in contact with said conductive shield;

an outer insulating layer molded about said conductive shield;

a disconnect switch interposed between the power source and said power cable;

a primary circuit for controlling said disconnect switch;

a secondary circuit connected to said drain wire for sensing a leakage current between said conductive shield and one of said insulated first wire and said insulated second wire and said insulated ground wire; and

an optical switch interconnecting said primary circuit and said secondary circuit for opening said disconnect switch upon said secondary circuit sensing a leakage current to disconnect said power cable from the power source.

22. An circuit for disconnecting a power source from a load, the power source having a line socket, a neutral socket and a ground socket, comprising:

a housing having a line lug, a neutral lug and a ground lug for insertion within said line socket, said neutral socket and said ground socket of the power source;

a power cord comprising an insulated line wire, an insulated neutral wire, an insulated ground wire;

said power cord having a conductive metallic foil shield surrounding said insulated line wire, said insulated neutral wire, said insulated ground wire;

a non-insulated drain wire contacting said conductive metallic foil shield;

an outer insulating layer molded about said conductive metallic foil shield urging mechanical and electrical contact between said conductive metallic foil shield and said non-insulated drain wire;

disconnect switch located in said housing interconnecting said line lug and said neutral lug of said housing to said insulated line wire and said insulated neutral wire of said power cord; and

said disconnect switch having a closed position whereat the power source is connected to the load and having an open position whereat the power source is disconnected from the load;

a primary circuit for controlling said disconnect switch;

a secondary circuit connected to said drain wire for sensing a leakage current between said conductive shield and one of said insulated first wire and said insulated second wire and said insulated ground wire; and

an optical switch interconnecting said primary circuit and said secondary circuit for opening said disconnect switch upon said secondary circuit sensing a leakage current to disconnect said power cable from the power source.