Patent ID: 8645087

Claim:
Method for measuring an earth fault current in an output circuit of an inverter (INU) operating on the PWM principle and forming alternating-current voltage from direct-current voltage, the output currents (i U , i V and i W ) of which inverter are measured, and which inverter comprises at least two phase switches implemented with power semiconductor components (V 1 -V 6 , D 1 -D 6 ), which switches, controlled by a control unit, connect their own output phases to a positive (+) pole and to a negative (−) pole of a direct-current voltage source such that the phase switches are repeatedly both in different positions and also in the same positions, characterized in that in the method the results of current measurement during two opposite switch position combinations are recorded in memory, and the earth fault current is calculated by forming a difference of the measurement results of said combinations.