Abstract: To determine an AC insulation resistance between the AC connections of an inverter and a ground potential, the AC connections are connected to an AC energy sink in an emergency standby operation in order to transmit energy from a DC energy source to an AC energy sink and an insulation test is performed in emergency standby operation. An AC fault current flowing between an AC connection and the ground potential is determined, and the AC insulation resistance is calculated from the AC fault current.

Abstract: The invention relates to an inverter (1) for converting a direct voltage (UDC) into an alternating voltage (UAC) for feeding into a single-phase three-conductor network (3) and for supplying loads (4), comprising a DC input (5), an intermediate circuit (6) having an intermediate circuit center point (7), a DC/AC converter (8) having at least two half bridges (12, 13), a control device (9), and an AC output (10) for connecting to the single-phase three-conductor network (3) and the loads (4?). The invention further relates to a method for operating such an inverter (1).