Abstract: An inverter application comprises at least one apparatus fed by an inverter (10). The determining of insulation defects is effected by way of a differential voltage of part voltages (U, U?) of an intermediate circuit (7) or the ratio of one of these part voltages (U, U?) to the total voltage of an intermediate circuit, and by way of an operating condition of the inverter (10). The monitoring of the insulation is carried out only with the means (1a, 1b, 1c, 1a?, 1b?, 1c?, 5, 5?) which are present in the inverter (10) in any case. The operating condition is set as a particular switch position in the inverter (10) by an insulation monitoring system. Alternatively, the operating condition is, while the inverter is on-line or in operation, transferred from the inverter control (9) to an insulation monitoring system for improving the quality of the monitoring.