The invention relates to a method for insulation fault location as well as to an insulation fault location system for an ungrounded power supply system.The main idea of the present invention rests upon the idea that while preserving a predetermined maximally admissible test current amplitude, a test current pulse duration of a test current is adaptively set such that all interfering values are eliminated in a captured differential current, in particular the leakage currents arising in consequence of large supply leakage capacitances.Should a test of the value of the final value of the differential current reveal that a test current threshold value has been exceeded, this exceedance can be seen as an indicator that the respective conductor section is therefore in the fault circuit.