Siemens SINAMICS G120 F30003: DC link voltage undervoltage
Cites the manual · line-by-line check pending
What it means DC link voltage dropped too low.
Likely causes
Line dip or loss
Phase missing
Checks, in order
Check supply and fuses
Source
Source (reworded, not copied): Siemens, SINAMICS G120 Control Units CU240B-2/CU240E-2 List Manual, 02/2023, A5E33839529, section 4.2 List of faults and alarms. Official manual (PDF). Fault numbers and names can differ between firmware versions.