Cable fault locator

Data records

• In the arc reflection method a reference trace recorded with a low-voltage pulse is overlaid on a trace recorded while an arc burns at the fault, the arc being struck by the sudden discharge of a charged capacitor into the cable; the arc produces a negative reflection, so the two traces diverge at the fault and that position is read as the fault distance. Source: Megger product page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.arc-reflection-method
• The first measurement stage identifies the faulted phase and whether the fault is of low or high resistance, because this decides the technique: a low-voltage pulse from a time-domain reflectometer sees a low-resistance fault, while a high-resistance fault is not visible to it and needs a surge (impulse) generator. Source: Megger application page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.fault-classification
• Cable fault location is described in five stages: the fault is first classified by type, then prelocated so that its distance from the test end is known, the cable route is traced, the exact position is pinpointed, and where several cables run together the faulted one is identified. Source: Megger product page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.five-stages
• On tape-shielded cables the impulse reflection techniques (arc reflection and impulse current) do not work reliably and a fault location bridge is used instead, whereas a dead short circuit is found more easily by a simple reflectometer test than by a surge generator. Source: HV Diagnostics product page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.method-fit
• Pinpointing takes place on the ground above the cable route while a surge generator (thumper) discharges into the cable repeatedly and causes a flashover at the fault; a ground microphone and an electromagnetic pickup detect the signals, and the fault lies where the time difference between the electromagnetic impulse and the slower acoustic signal is smallest. Source: Megger product page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.pinpointing
• Prelocation reports the distance to the fault; a low-resistance fault is often located by prelocation alone, while a high-resistance fault is prelocated by the arc reflection method or the impulse current method on a surge wave generator, or by the voltage decay method with a high-voltage direct-current source. Source: Megger application page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.prelocation-methods
• A cable fault locator is used wherever a fault on a buried or otherwise hidden cable cannot be seen; locating it is a multi-step procedure carried out on a cable that has been isolated and grounded at one or both ends before testing personnel approach it. Source: Megger application page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.purpose
• A failed sheath test on a direct-buried cable is followed by sheath fault location by the step voltage (ground gradient) method: the fault locator serves as a pulsed high-voltage source, and a separate receiver reads the strength and polarity of the ground gradient voltage, which rises when the fault is approached, falls to zero directly over it and reverses polarity beyond it. Source: Megger product page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.sheath-fault-location
• The lowest surge voltage that makes the fault appear is the one used, because the energy delivered to the cable rises with the square of the voltage and repeated surging at a much higher voltage can turn lesser points of damage into new insulation failures that need further repairs. Source: Megger application page, web page edition. Verified 2026-10-27. Record instr.cable-fault-locator.surge-voltage-selection