Undervoltage

Solar inverter DC bus undervoltage

This is caused by low intermediate circuit DC voltage. This can be caused by a missing supply voltage phase from a blown fuse or faulty isolator or contactor or internal rectifier bridge fault or simply low mains voltage. POSSIBLE FIXES: Check mains supply and fuses. . The "UN-BUS" error means the DC voltage level within the inverter is below the required threshold for proper operation. Insufficient DC voltage can. . Drive (VFD) undervoltage protection for common low HP drives is based on the measured voltage on the DC bus of the drive unit and not the input AC voltage. It is important to realize this fact to aid in troubleshooting.