Method for insulation monitoring of an inverter system in a test phase of the inverter system during starting of at least one electrical apparatus, wherein the inverter system comprises - an intermediate voltage circuit with at least one positive branch and a negative branch; - the 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: - in a first test configuration, switching-on of one switch element or simultaneously switching-on of multiple switch elements for connecting either the positive branch or the negative branch of the inverter to one or more phase connections, - measuring at least one of - a voltage of the positive branch and - a voltage of the negative branch; - determining values of characterizing variables of a function of at least one of these measured voltages; - determining insulation defects at the intermediate voltage circuit and/or at the phase connections and/or at the electrical apparatus by comparing these characterizing variables with corresponding reference values, and, if a deviation from the reference values exceeds a predetermined limit, signaling the presence of an insulation defect; - charging or discharging the intermediate circuit up or down to a reduced intermediate circuit voltage; - briefly applying different voltages to at least two phase connections (2a, 2b, 2c) by means of the switch elements of the inverter; - evaluating at least one resulting current and/or evaluating the triggering of a short circuit detector; and - determining, according to the result(s) of the evaluation(s), whether there is a short circuit between at least two of the phase connections (2a, 2b, 2c). - an intermediate voltage circuit with at least one positive branch and a negative branch; - the 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; - in a first test configuration, switching-on of one switch element or simultaneously switching-on of multiple switch elements for connecting either the positive branch or the negative branch of the inverter to one or more phase connections, - 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 values of characterizing variables of a function of at least one of these measured voltages; - determining insulation defects at the intermediate voltage circuit and/or at the phase connections and/or at the electrical apparatus by comparing these characterizing variables with corresponding reference values, and, if a deviation from the reference values exceeds a predetermined limit, signaling the presence of an insulation defect; - charging or discharging the intermediate circuit up or down to a reduced intermediate circuit voltage; - briefly applying different voltages to at least two phase connections (2a, 2b, 2c) by means of the switch elements of the inverter; - evaluating at least one resulting current and/or evaluating the triggering of a short circuit detector; and - determining, according to the result(s) of the evaluation(s), whether there is a short circuit between at least two of the phase connections (2a, 2b, 2c).