Fault detection circuit and method for testing a multiple conductor cable having a shield

Claim 2

A low current fault detection circuit for testing an out of service multiple conductor cable having an outer conductive shield, comprising: a multiple phase voltage source for providing a distinct voltage phase to each of a plurality of conductors in the cable; a current limiting device electrically connected between each of the distinct voltage phases and each of the conductors, means for electrically connecting the cable shield to ground; and indicator means electrically coupled in series between each of the conductors and said voltage source, said indicator means including means responsive to the potential difference between phases in conductors when the conductors are electrically shorted together, and between a phase and ground when a conductor is shorted to the cable shield, said indicator means further including means to indicate a phase to phase and a phase to ground short in the cable.

Claim 3

A fault detection circuit as in claim 1, wherein said current limiting device includes a variable resistor.

Claim 4

A fault detection circuit as in claim 1, further including fuse means electrically connected in series between each of said distinct voltage phases and each of the conductors.

Claim 5

A fault detection circuit as in claim 3, wherein said indicator means is connected between each of said distinct voltage phases and each of the conductors, said current limiting device is connected between each of said distinct voltage phases and said indicator means, and said fuse means is connected between each said distinct voltage phases and said current limiting device.

Claim 6

A fault detection circuit as in claim 1, wherein the multiple phase voltage source provides distinct voltage phases having a potential difference of about 220 volts AC phase-to-phase.

Claim 7

A fault detection circuit as in claim 5, wherein said multiple voltage source provides three phases to three of the conductors, said phases being about 120° apart from each other.

Claim 8

A fault detection circuit as in claim 1, wherein each of the conductors are removeably connected to the detection circuit.

Claim 9

A fault detection circuit as in claim 1, wherein said indicator means includes relay means.

Claim 10

A fault detection circuit as in claim 8, wherein said indicator means includes a relay connected in series between said voltage source and each of said conductors, the relay connected between one of the conductors and the voltage source being energized when the one conductor is shorted to the cable shield and the remaining relay(s) being non-energized when a phase-to-ground short occurs in the cable, and the relays connected between a pair of conductors and the voltage source being energized when the pair of conductors are shorted together and the remaining relay(s) being non-energized when a phase-to-phase short occurs in the cable.

Claim 11

A fault detection circuit as in claim 1, wherein said indicator means includes fault counter means, said fault counter means including illuminating lamp or analog counter means.

Claim 12

A fault detection circuit as in claim 1, wherein said means responsive further includes a logic circuit, said logic circuit including a power supply switch for providing power to said logic circuit, a reset switch having means for resetting said logic circuit before testing for faults, and means for indicating power-on and ready-to-test.

Claim 15

A method for testing multiple conductor cables for faults as in claim 12, further comprising the step of impacting a portion of the cable with a test block.

Claim 16

A method as in claim 13, further comprising the steps of: providing power to a test control circuit and energizing a first control relay, said first control relay closing one portion of the electrical path between said voltage source and said relay means, selectively energizing a second control relay, said energized second control relay in turn energizing a third control relay, said third control relay closing a second portion of the electrical path between said voltage source and said relay means and establishing a closed circuit therebetween, energizing a fourth control relay and activating a corresponding indicator means in response to a phase-to-phase or phase-to-ground fault in the cable, said indicator means having means to indicate the fault in the cable.

Claim 17

A method as in claim 14, further comprising the steps of: selectively energizing a fifth control relay and closing said second portion of the electrical path between said voltage source and said relay means and temporarily establishing a closed circuit therebetween, energizing said fourth control relay in response to a pre-existing fault in the cable, said indicator means having means to indicate said pre-existing fault in the cable.

Claim 18

A low current electrical testing system, comprising: a segment of a cable having a plurality of conductors and an outer conductive shield, said outer shield being electrically connected to ground and each of said conductors having one end which floats with respect to ground, and said cable being adapted to be impacted substantially transversely to its length, first means for providing a distinct voltage phase from a voltage source to the other end of each conductor, and second means responsive to the potential difference between said distinct voltage phases in conductors when the conductors are shorted together, and between a distinct voltage phase in a conductor and ground when a conductor is shorted to the cable shield, said second means including a current limiting device to limit the current through the conductors, and third means to indicate a phase to phase or a phase to ground short in the cable with a lamp or counting device.

Claim 19

A low current electrical testing system, comprising: a segment of a cable having a plurality of conductors and an outer conductive shield, said outer shield being electrically connected to ground and each of said conductors having one end which floats with respect to ground, and said cable being adapted to be impacted substantially transversely to its length, first means for providing a distinct voltage phase from a voltage source to the other end of each conductor, and second means responsive to the potential difference between said distinct voltage phases in conductors when the conductors are shorted together, and between a distinct voltage phase in a conductor and ground when a conductor is shorted to the cable shield, said second means including a current limiting device to limit the current through the conductors, and third means to indicate a phase to phase or a phase to ground short in the cable with a lamp or counting device.

Claim 20

An electrical testing system as in claim 16, wherein the outer shield is the outermost layer on the cable.

Claim 21

A low current fault detection circuit for testing a multiple conductor cable having an outer conductive shield, comprising: a multiple phase voltage source for providing a distinct voltage phase to one end of each of a plurality of conductors in the cable, the other end of each of the plurality of conductors being allowed to float with respect to ground; means for electrically connecting the cable shield to ground; a relay device electrically connected in series between each conductor and the voltage source for responding to the potential difference between phases in conductors when the conductors are electrically shorted together, and between a phase and ground when a conductor is shorted to the cable shield; a current limiting device electrically connected in series between each relay device and the voltage source for limiting the current in each shorted conductor; and a display device to visually indicate a phase to phase or a phase to ground short in the cable when any of said relay devices responds to a short in the cable.

Claim 22

A low current fault detection circuit for testing a multiple conductor cable having an outer conductive shield, comprising: a multiple phase voltage source for providing a distinct voltage phase to one end of each of a plurality of conductors in the cable, the other end of each of the plurality of conductors being allowed to float with respect to ground; means for electrically connecting the cable shield to ground; a relay device electrically connected in series between each conductor and the voltage source for responding to the potential difference between phases in conductors when the conductors are electrically shorted together, and between a phase and ground when a conductor is shorted to the cable shield; a current limiting device electrically connected in series between each relay device and the voltage source for limiting the current in each shorted conductor; and a display device to visually indicate a phase to phase or a phase to ground short in the cable when any of said relay devices responds to a short in the cable.

Claim 23

A low current electrical testing circuit, comprising: a segment of a cable having a plurality of conductors and a conductive armor shield, said conductive armor shield being electrically connected to ground and each of said conductors having one end which floats with respect to ground, a voltage source for providing a distinct voltage phase to the other end of each conductor, at least one current limiting device electrically connected between the voltage source and the conductors in the cable to limit the current through the conductors, at least one switching device electrically connected between the voltage source and the conductors in the cable which is responsive to the potential difference between said distinct voltage phases in conductors when the conductors are shorted together, and between a distinct voltage phase in a conductor and ground when a conductor is shorted to the grounded cable shield, an indicator device electrically connected to said at least one switching device to indicate a phase to phase or a phase to ground short in the cable.

Claim 24

A low current electrical testing circuit, comprising: a segment of a cable having a plurality of conductors and a conductive armor shield, said conductive armor shield being electrically connected to ground and each of said conductors having one end which floats with respect to ground, a voltage source for providing a distinct voltage phase to the other end of each conductor, at least one current limiting device electrically connected between the voltage source and the conductors in the cable to limit the current through the conductors, at least one switching device electrically connected between the voltage source and the conductors in the cable which is responsive to the potential difference between said distinct voltage phases in conductors when the conductors are shorted together, and between a distinct voltage phase in a conductor and ground when a conductor is shorted to the grounded cable shield, an indicator device electrically connected to said at least one switching device to indicate a phase to phase or a phase to ground short in the cable.

Claim 25

An electrical testing system as in claim 19, wherein the conductive armor shield is the outermost layer on the cable.