A method for determining whether an electric insulation of a conductor (11, 12) in an electric system is sufficient, such as in an electric system described as a resistor-capacitor circuit, the method comprising: - switching on or off a resistive load between the conductor (11, 12) and ground, - measuring a first voltage value u 1 of a resulting voltage U m between the conductor (11, 12) and ground at a predetermined first point in time t 1 after switching on or off the load, the method further comprising: - determining if the first voltage value u 1 fulfils a predetermined first condition, and/or - determining an initial rate of change of the resulting voltage U m between the conductor (11, 12) and ground over time based on the measured first voltage value u 1, and determining if the initial rate of change fulfils a predetermined second condition, characterized in - determining that the electric insulation is sufficient when at least one of the first and second conditions is fulfilled, wherein, when the electric insulation is not determined to be sufficient, the method further comprises: - predicting a voltage response U p over time between the conductor (11, 12) and ground by using the initial rate of change and assuming a linear response, - initiating a continuous measurement of the resulting voltage U m between the conductor (11, 12) and ground over time, and comparing the measured resulting voltage U m to the predicted voltage response U p, - determining a point in time when a relation between the measured resulting voltage U m and the predicted voltage response U p fulfils a predetermined third condition, and therefrom determining a time constant τ of the electric system and/or predicting a steady-state voltage u ss between the conductor (11, 12) and ground, - using the determined time constant τ and/or the predicted steady-state voltage u ss, estimating whether the electric insulation between the conductor (11, 12) and ground is sufficient. - switching on or off a resistive load between the conductor (11, 12) and ground, - measuring a first voltage value u 1 of a resulting voltage U m between the conductor (11, 12) and ground at a predetermined first point in time t 1 after switching on or off the load, - determining if the first voltage value u 1 fulfils a predetermined first condition, and/or - determining an initial rate of change of the resulting voltage U m between the conductor (11, 12) and ground over time based on the measured first voltage value u 1, and determining if the initial rate of change fulfils a predetermined second condition, - determining that the electric insulation is sufficient when at least one of the first and second conditions is fulfilled, - predicting a voltage response U p over time between the conductor (11, 12) and ground by using the initial rate of change and assuming a linear response, - initiating a continuous measurement of the resulting voltage U m between the conductor (11, 12) and ground over time, and comparing the measured resulting voltage U m to the predicted voltage response U p, - determining a point in time when a relation between the measured resulting voltage U m and the predicted voltage response U p fulfils a predetermined third condition, and therefrom determining a time constant τ of the electric system and/or predicting a steady-state voltage u ss between the conductor (11, 12) and ground, - using the determined time constant τ and/or the predicted steady-state voltage u ss, estimating whether the electric insulation between the conductor (11, 12) and ground is sufficient.