Siemens alarm F30027: Power unit: precharging DC link time monitoring
SINAMICS S120/G150 infeed fault · SINAMICS S120
What it means
DC link could not be pre-charged within the expected time (OFF2, immediate acknowledgement).
Likely causes
- no/too-low line supply or open line contactor
- pre-charge resistors blown or overheated (too frequent restarts)
- short circuit/ground fault on the DC link pulling charge down
- defective pre-charge circuit (chassis units)
- ruptured fuse in Motor Module (booksize) preventing bus formation
- line contactor closed during fast DC-link discharge by braking module
Triage note: Do NOT repeatedly power-cycle: pre-charge resistors overheat and fail, turning a supply issue into major repair. Wait ~8 min between attempts. Field case: blown pre-charge resistors + contactor after rapid restarts, plus 2 of 12 DC-link caps destroyed.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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pre-charge resistor set (chassis/infeed-specific)
pre-charge resistors · Primary suspect
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line contactor per electrical design
line contactor · Common cause
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6SL3120-…
Motor Module internal fuse/power stage (booksize, if r0070 shows no bus at MM) · Common cause
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6SL3130-… / SL chassis infeed
infeed unit (pre-charge electronics) · Common cause
Need the part urgently?
Send us alarm F30027 with your machine details — typical RFQ turnaround is 24–48h.