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.