Abstract: Apparatus for detecting and locating a fault in an electric cable or cable installation using a pulse-echo or impulse current technique comprises a low voltage pulse generator for injecting a series of pulses into a cable or cable installation; a digital store and memory for recording a predetermined number of pulses and for digitizing and storing the waveforms obtained under two different conditions of the cable; means for terminating the recording of pulses a predetermined time after a fault condition is detected; and means for retrieving the signals obtained under the two separate conditions, comparing them and thus locating the position of the fault.

Abstract: Apparatus for detecting and locating a fault in an electric cable using a pulse-echo technique comprises means for injecting step function or single pulses into a cable, means for digitizing and storing the pulse-echo signal obtained under two different conditions of the cable, and means for retrieving the signals obtained under the two said conditions, comparing them and thus locating the position of the fault. Preferably, the apparatus also includes means for detecting whether the cable is "live and healthy" or "live and faulty" by obtaining a digital pulse signal indicating that a voltage is present on the cable, obtaining a second digital pulse signal indicating by a series of pulses when the current in the cable is above the normal load current and gating these two signals in a NAND gate to obtain a signal representing the state of the cable.

Abstract: A fault in a cable comprising at least two conductors is located by applying a single voltage impulse between two conductors of the cable, passing the resultant current wave form through a primary winding of coupling means which comprises said primary winding and a secondary winding, the primary winding being connected in series between the impulse generator and one of said conductors and which obtains the derivative of said current wave form to give a signal output across the secondary winding, and displaying or recording the signal output. The signal output is a pulse of relatively short duration each time a reflection of the voltage impulse returns to the impulse generator. Preferably a digital transient recorder is used for recording the waveform of the resultant reflected signal from the cable.

Abstract: For detecting faults on low voltage alternating current electric power distribution cables, recorders are provided, each triggered by a selected occurrence, e.g. a decrease in signal amplitude or a change in the waveform, to cease recording, after a short delay, of the waveform data in digital form, so that a store holds digital data enabling the waveform of the last few cycles covering the period before and after the selected occurrence. Using a voltage gradient technique analysis of the data enables the position of the fault to be located.