A method for determining the elements of a dielectric equivalent circuit diagram for an insulation of an electric system, the equivalent circuit diagram being a parallel connection made up of a fault resistance (Rf), a leakage capacitance (Ce) and an absorption element which is made up of a series connection of an absorption resistance (R a) and an absorption capacitance (C a), the method comprising the steps: applying a voltage step to the electric system as a test voltage (uo (t)) of a voltage source having a known measurement resistance (R m) in series to the voltage source; measuring a voltage dropping at the measurement resistance (R m) as a step response (ua(t)) of the electric system; characterized by recording the step response (ua(t)) over a measuring period (T m) whose duration approximately corresponds to a two-fold settling phase of the step response (ua(t)); calculating the fault resistance (Rf) from the progression of the step response (ua(t)) in the settled state; determining the time constants (τ) from the progression of the step response (ua(t)) in the settling phase; calculating an initial value (C e0) of the leakage capacitance (Ce) from the time constants (τ), the fault resistance (R f) and the measurement resistance (R m); forming a transfer function (G(s)) of the electric system, which was modelled by the equivalent circuit diagram using the equivalent circuit diagram elements (Rf, C e, R a, C a) and the measurement resistance (R m), as a ratio between an output signal (U'a(s)) at the measurement resistance (R m) and a test signal (Uo(s)) of the voltage source as an input signal; calculating the output signal (U'a(s)) from the transfer function (G(s)) using a step function as a test signal (Uo(s)) while incorporating the calculated fault resistance (Rf), the calculated initial value (C e0) of the leakage capacitance (Ce) and the known measurement resistance (R m), the absorption resistance (R a), the absorption capacitance (C a) and the leakage capacitance (Ce) each being iteratively determined in such a manner via approximate values (R' a, C' a, C' e) by means of an approximation algorithm that the deviation between the calculated output signal (u' a (t)) transformed in the time range and the measured recorded step function (ua(t)) is minimized. applying a voltage step to the electric system as a test voltage (uo (t)) of a voltage source having a known measurement resistance (R m) in series to the voltage source; measuring a voltage dropping at the measurement resistance (R m) as a step response (ua(t)) of the electric system; characterized by recording the step response (ua(t)) over a measuring period (T m) whose duration approximately corresponds to a two-fold settling phase of the step response (ua(t)); calculating the fault resistance (Rf) from the progression of the step response (ua(t)) in the settled state; determining the time constants (τ) from the progression of the step response (ua(t)) in the settling phase; calculating an initial value (C e0) of the leakage capacitance (Ce) from the time constants (τ), the fault resistance (R f) and the measurement resistance (R m); forming a transfer function (G(s)) of the electric system, which was modelled by the equivalent circuit diagram using the equivalent circuit diagram elements (Rf, C e, R a, C a) and the measurement resistance (R m), as a ratio between an output signal (U'a(s)) at the measurement resistance (R m) and a test signal (Uo(s)) of the voltage source as an input signal; calculating the output signal (U'a(s)) from the transfer function (G(s)) using a step function as a test signal (Uo(s)) while incorporating the calculated fault resistance (Rf), the calculated initial value (C e0) of the leakage capacitance (Ce) and the known measurement resistance (R m), the absorption resistance (R a), the absorption capacitance (C a) and the leakage capacitance (Ce) each being iteratively determined in such a manner via approximate values (R' a, C' a, C' e) by means of an approximation algorithm that the deviation between the calculated output signal (u' a (t)) transformed in the time range and the measured recorded step function (ua(t)) is minimized.