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Ground monitoring system

  • US 4,228,475 A
  • Filed: 08/28/1978
  • Issued: 10/14/1980
  • Est. Priority Date: 08/28/1978
  • Status: Expired due to Term
First Claim
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1. In a ground wire sensor circuit for use with an electrical power cable that includes power conductors, at least one ground wire and at least one other wire that is not a power conductor, wherein said ground wire and other wire are joined together at one end of the power cable by a resistance means of given value, and wherein a sensing signal is coupled between the other ends of the ground and other wires to form a ground wire monitoring loop, said sensing signal being at a sensing frequency that is substantially different from that of the electrical power to be carried on the power conductors, and wherein the cable is connected to a source of power through circuit interrupting means,the method of testing the electrical condition of said loop, comprising the stepssubstantially blocking the sensing signal from leaving the loop at a region on the ground wire that is adjacent said resistance means,sampling the sensing signal voltage on said loop and producing a sampled voltage signal in response thereto,sampling the sensing signal current in said loop and producing a sampled current signal in response thereto,comparing the sampled voltage and current signals and producing a comparison output signal when a predetermined relationship exists between the compared signals,changing the condition of a circuit control means in response to the production of a comparison output signal,opening said circuit interrupting means to disconnect the power conductors of said cable from said source of power to response to said circuit control means changing conditions.

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