-Check engine body grounding.
-AC mains voltages may be outside programmed limits, measure the phase voltages.
-Check the AC voltage readings on the screen.
-Upper and lower limits of the mains voltages may be too tight. Check the parameters Mains Voltage Low Limit and Mains Voltage High Limit. Standard values are 170/270 volts.
-The hysteresis voltage may be given to excessive. The standard value is 8 volts.