A method for insulation fault location in an ungrounded power supply system, comprising the method steps to be carried out repeatedly: - generating a periodic test current by means of a test current generator, said test current comprising a predetermined maximum test current amplitude and a test current period having a changeable test current period duration and said test current period being compiled from temporally consecutive test current pulses and test current pauses, - feeding the test current into the ungrounded power supply system, - capturing a differential current in a cable section to be monitored,- determining a stationary steady state and a stationary decay state of the differential current and determining a respective settling time and decay time, - determining a final value (Ix) of the differential current in the corresponding steady state of the differential current, - testing whether the final value (Ix) of the differential current exceeds a test current threshold value according to magnitude in order to identify a capturable test current, - transmitting the value of the settling time and the decay time to the test current generator, - setting a test current pulse duration (T1, T3) and a test current pause duration (T2, T4) as a function of the transmitted settling time and decay time using the test current generator such that the differential current reaches its respective final value (Ix) within the test current pulse duration (T1, T3) and the test current pause duration (T2, T4), said predetermined maximum test current amplitude remaining unchanged - a first differential current base value from which the following test current pulse becomes settled being determined when the test current pulse has decayed, - a settling differential value being formed between the differential current final value (Ix) and the first differential current base value after supplying the test current pulse when the test current pulse has settled, - a second differential current base value to which the previous test current pulse has decayed being determined after the test current pulse has decayed, - a decay differential value being formed between the differential current final value (Ix) and the second differential current base value, - should the settling differential value coincide with the decay differential value within a tolerance range, a valid capture of the differential current is available in order to identify the capturable test current. - generating a periodic test current by means of a test current generator, said test current comprising a predetermined maximum test current amplitude and a test current period having a changeable test current period duration and said test current period being compiled from temporally consecutive test current pulses and test current pauses, - feeding the test current into the ungrounded power supply system, - capturing a differential current in a cable section to be monitored,- determining a stationary steady state and a stationary decay state of the differential current and determining a respective settling time and decay time, - determining a final value (Ix) of the differential current in the corresponding steady state of the differential current, - testing whether the final value (Ix) of the differential current exceeds a test current threshold value according to magnitude in order to identify a capturable test current, - transmitting the value of the settling time and the decay time to the test current generator, - setting a test current pulse duration (T1, T3) and a test current pause duration (T2, T4) as a function of the transmitted settling time and decay time using the test current generator such that the differential current reaches its respective final value (Ix) within the test current pulse duration (T1, T3) and the test current pause duration (T2, T4), said predetermined maximum test current amplitude remaining unchanged - a first differential current base value from which the following test current pulse becomes settled being determined when the test current pulse has decayed, - a settling differential value being formed between the differential current final value (Ix) and the first differential current base value after supplying the test current pulse when the test current pulse has settled, - a second differential current base value to which the previous test current pulse has decayed being determined after the test current pulse has decayed, - a decay differential value being formed between the differential current final value (Ix) and the second differential current base value, - should the settling differential value coincide with the decay differential value within a tolerance range, a valid capture of the differential current is available in order to identify the capturable test current.