Voltage indicating coupling for metal conduit systems

• US 8,058,879 B1
• Filed: 01/06/2009
• Issued: 11/15/2011
• Est. Priority Date: 01/06/2009
• Status: Expired due to Fees

• Current Assignee: John C. Atherton
• Original Assignee: John C. Atherton
• Inventors: Atherton, John C.
• Primary Examiner(s): Dole; Timothy J
• Assistant Examiner(s): Baldridge; Benjamin M
• Application Number:
  US12/349,314
• Time in Patent Office: 1,043 Days
• Field of Search: 324/510
• US Class Current: 324/510
• CPC Class Codes: G01R 19/155 Indicating the presence of voltage

Abstract

A voltage indicating coupling for metal conduit systems to indicate the presence or absence of voltage on a wire enclosed by a section of electrical conduit for a grounded AC power distribution system. Through the use of two opposing rectifiers the National Electrical Code requirement that the entire metal conduit system be grounded is met. The voltage indicating coupling comprises a liquid crystal display (LCD), a static suppression resistor, two opposing rectifiers for grounding purposes, a plastic block housing and two clamping screws with corresponding wire terminals. At least one “hot” conductor enclosed by the section of electrical conduit is capacitively coupled to the conduit creating a complete circuit through the liquid crystal display (LCD), the static suppression resistor and the opposing rectifiers. The path around the circuit is completed by a ground connection on the grounded part of the conduit system, and the ground connection at the transformer.

Claims

1. A coupling for mounting in a metal conduit system for indicating the presence or absence of AC voltage on an insulated conductor enclosed by a first, ungrounded section of the metal conduit system, said coupling comprising:

a body of electrically insulating material for location between and in mechanical engagement with both the first section of the metal conduit system and a second, grounded section of the metal conduit system, whereby the body of electrically insulating material does not provide electrical connection between the first section of the metal conduit system and the second section of the metal conduit system, and

a status indicating means attached to and supported by the body of electrically insulating material, the status indicating means comprising a high impedance display device having at least first and second display electrodes for connection to the first section and the second section respectively of the metal conduit system, a static suppression resistor connected between the first and second display electrodes, and two opposing unidirectionally conductive devices connected in series opposition between the first and second display electrodes, each unidirectionally conductive device having a reverse breakdown voltage that is less than a nominal voltage relative to ground of the insulated conductor,

whereby in normal operation and use the presence or absence of voltage on the insulated conductor is indicated by the appearance of said display device and in the event that the conductor is shorted to the first section of the metal conduit system and the conductor is at a voltage relative to ground at least as high as said nominal voltage the unidirectionally conductive devices ground the first section to the second section.

2. A coupling according to claim 1, wherein the high impedance display device is a liquid crystal display device.

3. A coupling according to claim 1, wherein the two unidirectionally conductive devices are diodes having their cathodes connected together and their anodes connected to the first and second display electrodes respectively.

4. A electrical power distribution system comprising:

a first section of metal conduit,

a second section of metal conduit,

an insulated conductor extending through both the first section and the second section of metal conduit,

a body of electrically insulating material located between and in mechanical engagement with both the first section of metal conduit and the second section of metal conduit, whereby the body of electrically insulating material does not provide electrical connection between the first section and the second section, and

a status indicating means attached to and supported by the body of electrically insulating material, the status indicating means comprising a high impedance display device having at least first and second display electrodes connected to the first section and the second section respectively, a static suppression resistor connected between the first and second display electrodes, and two opposing unidirectionally conductive devices connected in series opposition between the first and second display electrodes, each unidirectionally conductive device having a reverse breakdown voltage that is less than a nominal voltage relative to ground of the insulated conductor,

whereby in normal operation and use the first section of metal conduit is grounded, the second section of metal conduit is ungrounded, and the presence or absence of voltage on the insulated conductor is indicated by the appearance of said display device and in the event that the conductor is at a voltage relative to ground at least as high as said nominal voltage and the conductor is shorted to the second section of metal conduit, the unidirectionally conductive devices ground the second section to the first section.

5. A power distribution system according to claim 4, wherein the high impedance display device is a liquid crystal display device.

6. A power distribution system according to claim 4, wherein the two unidirectionally conductive devices are diodes having their cathodes connected together and their anodes connected to the first and second display electrodes respectively.

7. A electrical power distribution system comprising:

a first, ungrounded section of metal conduit,

a second, grounded section of metal conduit,

an insulated conductor extending through both the first section and the second section of metal conduit and at a voltage relative to ground at least as high as a nominal voltage,

a body of electrically insulating material located between and in mechanical engagement with both the first section of metal conduit and the second section of metal conduit, whereby the body of electrically insulating material does not provide electrical connection between the first section and the second section, and

a status indicating means attached to and supported by the body of electrically insulating material, the status indicating means comprising a high impedance display device having at least first and second display electrodes connected to the first section and the second section respectively, a static suppression resistor connected between the first and second display electrodes, and two opposing unidirectionally conductive devices connected in series opposition between the first and second display electrodes, each unidirectionally conductive device having a reverse breakdown voltage that is less than said nominal voltage,

whereby in normal operation and use the presence or absence of voltage on the insulated conductor is indicated by the appearance of said display device and in the event that the conductor is at a voltage relative to ground at least as high as said nominal voltage, and the conductor is shorted to the first section of metal conduit, the unidirectionally conductive devices ground the first section to the second section.

8. A power distribution system according to claim 7, wherein the high impedance display device is a liquid crystal display device.

9. A power distribution system according to claim 8, wherein the two unidirectionally conductive devices are diodes having their cathodes connected together and their anodes connected to the first and second display electrodes respectively.