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Fault indicator having increased sensitivity to fault currents

  • US 4,424,512 A
  • Filed: 08/12/1982
  • Issued: 01/03/1984
  • Est. Priority Date: 09/25/1980
  • Status: Expired due to Fees
First Claim
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1. A fault indicator responsive to the occurrence of a fault current at or above a predetermined minimum threshold level in an alternating current conductor, comprising, in combination:

  • a housing including means for attaching the housing to the conductor;

    indicator means within said housing having a reset-indicating state and a fault-indicating state;

    electric circuit means within said housing for conditioning said indicator means to said fault-indicating state in response to a contact closure;

    first and second magnetic reed switch elements arranged in parallel-spaced relationship to respective parallel-spaced planes each generally perpendicular to the axis of said conductor, said switch elements being in magnetic communication with said conductor and each including a pair of contacts actuated only upon the occurrence of a current in said conductor in excess of said predetermined threshold level;

    said magnetic reed switch elements each including an elongated housing having magnetically and electrically conductive wire leads extending from the ends thereof;

    the lead on one end of said first switch elements being electrically and magnetically connected to the lead on the adjacent end of said second switch elements, the remaining leads of said switch elements being arranged in parallel-spaced relationship to each other and to the axis of said switch elements;

    a magnetically non-conductive and electrically conductive bridging element connected between said parallel-spaced switch leads, said circuit means being connected to said bridging element and to said connected leads whereby said indicator means are conditioned to a fault indicating state upon closure of either of said contacts of said switch elements; and

    permanent magnet means mounted with the opposing poles thereof in communication with respective ones of said parallel spaced leads for establishing a magnetic bias circuit which serially includes said contacts of said magnetic switch elements, whereby said switch elements actuate upon the occurrence of a fault current at or above said threshold level during respective half cycles of the alternating current in the conductor, and return to a non-actuated state following termination of the fault current.

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