Siemens alarm F30040: Power unit: Undervolt 24 V
SINAMICS S120 drive fault · SINAMICS S120
What it means
The 24 V electronics supply of the power unit dropped below the undervoltage threshold for longer than 3 ms, forcing OFF2. On Servo drive objects the same code covers both the 24 V channel (yy=0) and the internal 48 V channel (yy=1), coded in the hex fault value. Momentary dips from a weak or overloaded external 24 V supply are the typical trigger; POWER ON required after correction.
Likely causes
- weak or failing 24 V PSU feeding X124/electronics bus
- overloaded 24 V distribution (too many modules on one feed)
- loose 24 V terminal or intermittent wiring
- internal electronics supply fault of the module
Triage note: Servo MMs display 'Undervolt 24/48 V' with channel coding in r0949.
Need the part urgently?
Send us alarm F30040 with your machine details — typical RFQ turnaround is 24–48h.