Method and directional system for the detection of ground faults in dc systems of isolated cables. Method and system for detection of ground faults for cable networks direct current (3) comprising at least one screen (4) for grounding (8) in a cable (3), a measuring equipment (5) of current which circulates through the screen (4) and obtains a current measurement signal (13), an analyzer device (12) of the measurement signal (13) and an intensity adjustment signal (14) circulating through the screen (4), which in turn comprises: - means for obtaining a current polarity value (16) and an intensity value of the measurement signal (13), - a divider (15) that compares the intensity of the intensity measurement signal (13) with the adjustment signal (14), - a comparator (18) that compares the intensity polarity (16) with a previously defined polarity sign, - means for generating a trigger signal (11), which indicates a defect (19) in the cable (3), from the output signals of the divider (15) and the comparator (18). (Machine-translation by Google Translate, not legally binding)