Intelligent ground fault circuit interrupter

• US 5,600,524 A
• Filed: 05/04/1995
• Issued: 02/04/1997
• Est. Priority Date: 05/04/1995
• Status: Expired due to Term

• Current Assignee: Leviton Manufacturing Company Incorporated
• Original Assignee: Leviton Manufacturing Company Incorporated
• Inventors: Gershen, Bernard, Neiger, Benjamin, Rosenbaum, Saul
• Primary Examiner(s): Gaffin, Jeffrey A.
• Assistant Examiner(s): JACKSON, STEPHEN W
• Application Number:
  US08/435,021
• Time in Patent Office: 642 Days
• Field of Search: 361/42, 361/45, 361/93, 361/115, 361/49, 361/50, 340/650
• US Class Current: 361/42
• CPC Class Codes: H02H 1/04 Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks
• CPC Class Codes: H02H 1/06 Arrangements for supplying operative power power supply arrangements in general G05F, H02M
• CPC Class Codes: H02H 11/002 in case of inverted polarity or connection; with switching for obtaining correct connection
• CPC Class Codes: H02H 3/05 with means for increasing reliability, e.g. redundancy arrangements for logic circuits H03K19/003
• CPC Class Codes: H02H 3/335 the main function being self testing of the device
• CPC Class Codes: H02H 3/337 avoiding disconnection due to reactive fault currents
• CPC Class Codes: H02H 3/338 also responsive to wiring error, e.g. loss of neutral, break
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities

Abstract

An intelligent circuit interrupt system is electrically connected between an AC source and a load for interrupting a flow of AC from the source to the load upon detection of an interrupt condition. A circuit interrupter electrically connected to phase and neutral terminals of the AC source defines the interrupt condition. A relay switch with a relay coil and phase and neutral contacts is included such that line and load ends of the phase contact are electrically connected, respectively, between the interrupt means load side phase port and a phase terminal of the load. Line and load ends of the neutral contact are electrically connected, respectively, between the interrupt neutral port and a neutral terminal of the load. The relay coil is electrically coupled between load sides of said phase and neutral contacts for controlling the contacts in response to the interrupt signal. An open-contact miswiring detector (OCMD) is electrically connected to one of the phase and neutral contacts for detecting a miswiring condition when the contacts are in an open state, and a closed-contact miswiring detector (CCMD) is electrically connected to the OCMD and to one of the neutral and phase contacts for detecting a miswiring condition when the contacts are in a closed state. A timing signal generator generates system timing signals. A test circuit electrically coupled to the interrupt means and the timing signal generator tests the interrupt means operability. An alarm circuit is electrically responsive to the test circuit, the timing signal generator, the OCMD and the CCMD for, communicating an open-contact miswiring condition, a closed-contact miswiring condition, an operational failure condition, and a need for external testing condition. A power supply is electrically connected between the load ends of the phase and neutral contacts, and to the timing signal generator.

Claims

1. An intelligent circuit interrupt system electrically connected load upon detection of an interrupt condition, comprising:

circuit interrupt means including line and load side phase and neutral ports, wherein said line side phase and neutral ports are electrically connected, respectively, to phase and neutral terminals of said AC source and said circuit interrupt mean generate an interrupt signal for interrupting said AC flow at detection of said interrupt condition;

a relay switch including a relay coil and phase and neutral contacts, wherein line and load ends of said phase contact are electrically connected, respectively, between said interrupt means load side phase port and a phase terminal of said load, line and load ends of said neutral contact are electrically connected, respectively, between said interrupt means load side neutral port and a neutral terminal of said load and said relay coil is electrically coupled between said load ends of said phase and neutral contacts for controlling said contacts in response to said interrupt signal;

an open-contact miswiring detector (OCMD) electrically connected to said line and load ends of one of said phase and neutral contacts for detecting a miswiring condition when said contacts are in an open state;

a closed-contact miswiring detector (CCMD) electrically connected to said load end of said phase contact and to said line and load ends of one of said neutral and phase contacts for detecting a miswiring condition when said contacts are in a closed state;

a timing signal generator electrically connected to said open and closed contact miswiring detectors for generating system timing signals;

a test circuit electrically coupled to said interrupt means and responsive to said timing signal generator for regularly testing said interrupt means'"'"' operability;

an alarm circuit electrically responsive to each of;

said test circuit, said timing signal generator, said open contact miswiring detector and said closed contact miswiring detector for communicating at least one of;

an open-contact miswiring condition, a closed-contact miswiring condition, an operational failure condition, and a need for external testing condition; and

a power supply electrically connected between said load ends of said phase and neutral contacts, and to said timing signal generator.

2. The intelligent circuit interrupt system defined by claim 1, wherein said interrupt circuit monitors a line current flowing from said source to said load and a neutral current flowing from said load to said source, and generates said interrupt signal based on a detected difference between said line and neutral currents.

3. The intelligent circuit interrupter system defined by claim 1, wherein said circuit interrupt means comprises a ground fault interrupt circuit.

4. The intelligent circuit interrupter system defined by claim 1, wherein said interrupt signal causes said relay coil to trip said relay contacts to an open state.

5. The intelligent circuit interrupter system defined by claim 1, wherein said miswiring conditions arise from a detection of one of said AC source phase and neutral terminals electrically connected, respectively, to one of said load ends of said phase and neutral contacts.

6. The intelligent circuit interrupter system as defined by claim 1, wherein said alarm circuit includes a piezoelectric transducer for generating at least one frequency-dependent alarm signal.

7. The intelligent circuit interrupter system as defined by claim 1, wherein said test circuit implements a self test at least every 2 hours.

8. The intelligent circuit interrupt system defined by claim 1, further including a surge suppressor electrically connected across said interrupt means line side phase and neutral ports.

9. The intelligent interrupter system as defined by claim 8, wherein said surge suppressor includes a metal oxide varistor.

10. The intelligent circuit interrupter system defined by claim 1, wherein said alarm circuit indicates a need for a user to test said system at least every 30 days.

11. The intelligent circuit interrupt system of claim 10, wherein said alarm circuit regularly communicates said need to test said system pursuant to said need to test indication until said system is tested by said user, except during other than daylight hours.

12. The intelligent circuit interrupt system defined by claim 1, further including automatic gain control means electrically coupled to said interrupt means for providing an adjust signal to said circuit interrupt means to vary a definition of said interrupt condition.

13. The intelligent circuit interrupt system defined by claim 12, wherein said automatic gain control means tracks and defines leakage current losses within said system and automatically adjusts said adjust signal to compensate therefor.

14. The intelligent circuit interrupt system defined by claim 13, wherein automatic gain control means adjusts for slowly varying leakage currents of try to 25 ma.

15. The intelligent circuit interrupt system defined by claim 13, wherein said interrupt signal interrupts said flow of AC at detection of a leakage current of at least 5 ma. determined to have changed abruptly.

16. A method of detecting ground faults at a load side of an interrupt circuit electrically connected between an AC source and a load such that AC flowing through said circuit is reliably interrupted upon detection of an interrupt condition by said circuit, comprising the steps of:

detecting a first mount of AC flowing from said AC source to said load utilizing said interrupt circuit;

detecting a second amount of AC flowing from said load to said AC source utilizing said interrupt circuit;

generating a difference signal indicative of a difference between said first and second amounts;

comparing said difference signal to a reference signal which is proportional to a maximum AC flow difference to define an interrupt condition in response thereto;

interrupting said flow of AC upon occurrence of said condition;

monitoring said circuit and identifying alarm conditions which require user intervention to assure reliable ground fault detection;

wherein said alarm conditions are determined on occurrence of an interrupt circuit miswiring detection, a detection of an inoperative condition within said interrupt circuit and a detection of a time which requires user assistance in testing said interrupt circuit operability; and

generating an alarm signal appropriate for communicating to a user a need for said intervention.

17. A method of detecting ground faults at a load side of an interrupt circuit electrically connected between an AC source and a load such hat AC flowing through said circuit is reliably interrupted upon detection of an interrupt condition by said circuit, comprising the steps of:

detecting a first amount of AC flowing from said AC source to said load utilizing said interrupt circuit;

detecting a second amount of AC flowing from said load to said AC source utilizing said interrupt circuit;

generating a difference signal indicative of a difference between said first and second amounts;

comparing in a comparator said difference signal to a reference signal which is proportional to a maximum AC flow difference to define an interrupt condition in response thereto;

interrupting said flow of AC upon occurrence of said condition;

monitoring said circuit and identifying alarm conditions which require user intervention to assure reliable ground fault detection;

generating an alarm signal appropriate for communicating to a user a need for said intervention,

wherein said alarm conditions are determined on occurrence of an interrupt circuit miswiring detection, a detection of an inoperative condition within said interrupt circuit and a detection of a time which requires user assistance in testing said interrupt circuit operability;

generating an alarm signal appropriate for communicating to a user a need for said intervention; and

adjusting a sensitivity of said comparator in accordance with non-alarm condition leakage current detection, including a comparison of a detected rate of change of leakage current determined during said step of comparing.