SAFETY CIRCUIT

• US 3,766,435 A
• Filed: 01/15/1973
• Issued: 10/16/1973
• Est. Priority Date: 01/15/1973
• Status: Expired due to Term

• Current Assignee: Kennie Childers
• Original Assignee: Kennie Childers
• Inventors: Childers, Kennie
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Fendelman, Harvey
• Application Number:
  US05/323,701
• Time in Patent Office: 274 Days
• Field of Search: 317/18R,18A,18C,9A,9D,31,53 340/255
• US Class Current: 361/42
• CPC Class Codes: H02H 3/105 responsive to excess current and fault current to earth
• 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

Abstract

The safety circuit protects against ground fault hazards in a direct current machine actuated from a D. C. source and incorporates means for detecting current flow from each of positive and negative legs of the D. C. lines to ground, either simultaneously or individually, and provides an indication thereof. Interrupting means responsive to the detector indication disconnects the machine from the power source upon the occurrence of the ground fault. The circuit also provides protection against overloads.

Claims

1. An arrangement for detecting positive and negative ground faults in a D. C. circuit, comprising:

a D. C. source applied to positive and negative terminals;

a device operable upon application of D. C. thereto;

a first circuIt connecting said positive terminal to the device;

a second circuit connecting said negative terminal to the device;

a first interrupting means in at least one of said first and second circuits;

a third circuit interconnected between said first and second circuits, said third circuit including second and third interrupting means and further including means for operating said first interrupting means;

a fourth circuit interconnected between said first and second circuits and including separate means for respectively operating said second and third interrupting means; and

circuit means interconnected with said fourth circuit and responsive to the presence of positive and negative ground faults, occurring both individually and simultaneously, to control current flow through said separate operating means thereby selectively actuating the second and third interrupting means to in turn control current flow through the operating means in said third circuit thereby actuating the first interrupting means to disconnect said device from the D. C. source.

2. An arrangement as set forth in claim 1, further comprising:

separate indicating means, operatively related to said second and third interrupting means, for supplying an indication of the existence of a ground fault upon actuation of the respective interruption means.

3. An arrangement as set forth in claim 1, wherein said interrupting means comprise relay contactors and the operating means comprise relays.

4. An arrangement as set forth in claim 3, wherein said relays are of the fusible type.

5. An arrangement as set forth in claim 3, wherein said fourth circuit includes a pair of relays connected in series with, and separated by, a resistor;

and wherein the circuit means interconnected with the fourth circuit includes a pair of series-joined diodes connected in parallel with the resistor and being oppositely poled with respect thereto, the junction between the diodes being electrically connected to ground.

6. An arrangement as set forth in claim 5, wherein the electrical connection of the diode junction to ground includes a variable resistor.

7. An arrangement as set forth in claim 6, wherein said relays are of the fusible type.

8. An arrangement as set forth in claim 7, further including:

separate indicating means, operatively related to the contactors which comprise the second and third interrupting means, for supplying an indication of the existence of a ground fault upon actuation of the respective contactor.

9. A safety circuit for detecting ground faults in a device actuated from D. C. input lines, comprising:

detector means for detecting current flow from each of positive and negative legs of the lines to ground occurring both simultaneously and individually and providing indication thereof including;

two serially coupled relays across the lines from positive to negative and a current limiting resistor interposed therebetween;

two diodes coupled in parallel in opposite polarities each at an end of the current limiting resistor, the diodes being commonly connected together at the other ends, and a sensitivity potentiometer coupled between ground and the common connection of the diodes;

each of the relays have at least one associated contact serially coupled together, controlled thereby to remain normally closed due to normal energization of the relays;

the indication of a ground fault occurring when at least one of said relays becomes de-energized, opening its associated contact; and

an interrupter means responsive to the detector means indication for interrupting input power to the device in response to the detection of a ground fault including;

a main relay coupled with and responsive to the serially coupled relay contacts, said main relay and serial contacts coupled between the positive and negative lines for completing a circuit and establishing said main relay normally energized; and

normally closed contacts for each leg of the Power input controlled by the main relay for simultaneously decoupling the device from power whenever the main relay is de-energized due to an indication of said detector means.

10. The safety circuit of claim 9, wherein said interrupter means includes a serially coupled resistor for establishing a current limit in the interrupter circuit.

11. The safety circuit of claim 10, wherein each of said relays are of the fusible type such that an overload of current in any of the respective circuits results in any of said normally closed contacts becoming open circuited to thereby decouple the device from power.

12. The safety circuit of claim 10, further including:

indication means responsive to the respective relay contacts of the detector circuit for providing respective indication of both positive and negative ground faults, said indication means including light-emitting means energized in response to the respective positive and negative fault.

13. The safety circuit of claim 12, wherein the light emitting means is coupled through a respective back contact of said detector relay.