Method for insulation monitoring of an inverter application during a normal operation of the inverter application, wherein the inverter application comprises: - an intermediate voltage circuit with at least one positive branch and a negative branch; - at least one electrical apparatus which comprises at least two phase connections; and - at least one inverter comprising switch elements for the electrical connection of the phase connections to the positive branch or the negative branch of the intermediate voltage circuit; and wherein the method comprises the following steps: - determining an operating condition of the inverter while the inverter is in operation and feeds the electrical apparatus which likewise is in a normal operation by acquiring parameters of an inverter control; - measuring at least one of - a voltage of the positive branch and - a voltage of the negative branch; - determining insulation defects at the intermediate voltage circuit and/or at the phase connections and/or at the electrical apparatus in accordance with the measured voltage or voltages and the operating condition of the inverter, wherein the method is characterized by the following steps: - filtering a voltage function and determining signal proportions of the voltage function in frequency ranges corresponding to an output frequency or a modulation frequency of the inverter, wherein the voltage function is a difference of partial voltages of the intermediate circuit voltages, or a ratio of a partial voltage to the total voltage of the intermediate circuit, or an individual partial voltage; and - comparing an amplitude of the voltage function filtered in such a manner, or a total energy of a plurality of voltage functions filtered in such a manner to a reference value, and, if this reference value is exceeded, signaling the presence of an insulation defect. - an intermediate voltage circuit with at least one positive branch and a negative branch; - at least one electrical apparatus which comprises at least two phase connections; and - at least one inverter comprising switch elements for the electrical connection of the phase connections to the positive branch or the negative branch of the intermediate voltage circuit; - determining an operating condition of the inverter while the inverter is in operation and feeds the electrical apparatus which likewise is in a normal operation by acquiring parameters of an inverter control; - measuring at least one of - a voltage of the positive branch and - a voltage of the negative branch; - a voltage of the positive branch and - a voltage of the negative branch; - determining insulation defects at the intermediate voltage circuit and/or at the phase connections and/or at the electrical apparatus in accordance with the measured voltage or voltages and the operating condition of the inverter, - filtering a voltage function and determining signal proportions of the voltage function in frequency ranges corresponding to an output frequency or a modulation frequency of the inverter, wherein the voltage function is a difference of partial voltages of the intermediate circuit voltages, or a ratio of a partial voltage to the total voltage of the intermediate circuit, or an individual partial voltage; and - comparing an amplitude of the voltage function filtered in such a manner, or a total energy of a plurality of voltage functions filtered in such a manner to a reference value, and, if this reference value is exceeded, signaling the presence of an insulation defect.