VFD input fuses
Match fuse class, voltage, amp rating, and cabinet documentation before replacing a blown SINAMICS input fuse.
$15-$80
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Siemens SINAMICS F30003 Fault Meaning
Siemens SINAMICS F30003 is a power-unit DC link undervoltage fault. The drive is seeing less DC bus voltage than it needs to run the inverter stage reliably.
On G120 drives, this usually points to the incoming supply, input fuses, terminals, contactor, line reactor, or PM power module. On S120 systems, it can also point to the Line Module that supplies the DC bus for the connected Motor Modules.
Common Causes
- Missing or weak input phase.
- Blown input fuse or wrong fuse rating.
- Loose L1, L2, or L3 terminal after vibration or panel service.
- Main contactor drop-out, coil chatter, or safety circuit interruption.
- Facility voltage dip when another large load starts.
- Undersized supply transformer or long feeder with voltage drop.
- Faulty line reactor, disconnect, or upstream protection device.
- Failing power unit after supply checks pass.
F30003 Checks {#f30003-checks}
- Lock out the cabinet and inspect the line side first. Look for heat marks, loose terminals, damaged fuse holders, and contactor discoloration.
- Verify every input fuse against the panel drawing. A single open fuse can leave the drive display alive while the DC bus collapses when the drive tries to run.
- Measure input voltage phase to phase at the drive input with a rated meter. Compare L1-L2, L2-L3, and L1-L3 instead of trusting one reading.
- Watch whether the fault happens at power-up, run command, acceleration, or when another machine starts. Timing often separates facility supply dips from drive hardware failure.
- Check the contactor and safety chain. A contactor that drops for a split second can create F30003 even when static voltage readings look normal.
- If the incoming power stays stable, check the DC bus reading in Startdrive, STARTER, the BOP-2, or the machine HMI. Use qualified personnel only because DC bus work is hazardous.
- Back up parameters before replacing a power module, Line Module, or Control Unit.
What to Check by System
| System | F30003 focus |
|---|---|
| SINAMICS G120 / G120C | Input fuses, incoming phase loss, PM terminals, line reactor, main contactor |
| SINAMICS S120 | Line Module status, DC bus supply, input fuses, DRIVE-CLiQ fault context |
| SINUMERIK CNC with S120 | Full 25xxx alarm text plus the underlying SINAMICS drive fault |
| Pump or fan panels | Utility dips, soft power loss, contactor chatter, and undersized feeder |
Parts and Tools
F30003 is usually an input-power diagnosis before it is a drive replacement. Start with verified fuses, a rated meter, and cabinet hardware that matches the panel documentation. Do not replace a SINAMICS power module until the incoming supply and DC bus behavior have been documented.