A system comprising a portable apparatus and employing a method of admittance versus frequency analysis to detect the existence of a fault in a de-energized electrical line regardless of whether the line contains branches. The portable apparatus comprises a capacitor unit detachably connected to a de-energized line, ground or a neutral conductor, a switch unit detachably connected to a de-energized line, the de-energized line being tested, and an insulated cable connecting the capacitor unit to the switch unit. The switch unit comprises a discharge switch that can be activated by pulling on the hot line tool. The capacitor unit comprises a capacitor which is discharged into the electrical line via the insulated cable and the switch unit when the discharge switch is activated to create a pulse. The capacitor unit comprises circuitry for generating voltage and current samples of pulse response signals and a microprocessor for determining the admittance of the electrical line using Fast Fourier transforms of the current and voltage samples. The admittance of the line is compared with stored data relating to lines having different load impedances and having faults located at various distances from the capacitor unit and detectable at various frequencies to determine the existence of a fault.