Troubleshoot a VFD in a fixed order: isolate and prove the DC bus is discharged, record the fault and operating values before resetting, decide which layer of the control chain is involved, then use when it tripped (accelerating, decelerating, supply dip) to narrow the cause. Change one thing at a time and record the result.
- The DC link stays lethal after mains-off.
- Evidence first, reset second.
- Trip timing points to the cause.
- Never up-size protection to stop a trip.
Safety First: Isolation and DC Bus Discharge
Isolate according to the manufacturer and plant procedure, wait the discharge time on the drive label, and confirm with a correctly rated instrument.
G120C on BOP-2 (simplified)
- r0026 DC link voltage (monitor)
Solution using STARTER
- While the drive is still live, read
r0026(DC link voltage) in the STARTER expert list or on the BOP-2 to know what you are dealing with. - Isolate and lock off the mains. If the control unit is on external 24 V, STARTER stays online, but that tells you nothing about the power section’s stored energy.
- Wait the discharge time on the drive label, then measure at the DC/motor terminals with a correctly rated meter. Never use a software value as proof of zero energy.
r0026Record Before You Reset
Write down the fault code, frequency, current, DC bus voltage, temperature, motor state and process condition before pressing reset. Use the fault record below, which the fault finder can fill for you.
G120C on BOP-2 (simplified)
- F30002 fault active
- r0945 fault buffer
- r0949 fault value
Solution using STARTER
- Before acknowledging, go online in STARTER and open the Alarms window (bottom of the screen): note code, text and time.
- In the expert list read the fault buffer:
r0945(fault codes),r0949(fault values, which give extra detail) andr0948(time received). - Copy operating values:
r0021speed,r0027current,r0026DC link,r0035motor temperature. Then acknowledge.
r0945r0948r0949r0021r0027r0026Fault record
A repeatable record turns breakdown experience into preventive knowledge. Template from softwellautomation.com.
Understand the Control Chain
G120C on BOP-2 (simplified)
- F30011 line phase failure
- F30003 DC link undervoltage
- F30021 ground fault
- F07801 motor overcurrent
- F07900 motor blocked
- F08501 PROFINET setpoint timeout
- r0046 missing enables
Solution using STARTER
- Read the code in the STARTER Alarms window and open its help text for the cause and remedy for your firmware.
- Use the fault value
r0949to narrow the layer: it often states which phase, limit or interface was involved. - Map the code to a layer before changing parameters: 300xx codes point at supply, DC bus or power unit; 07xxx at motor or control; 08501/01910 at communication.
r0949Practise fault finding on real drives
Hands-on VFD troubleshooting with planted faults on SINAMICS hardware — Pune classroom, online, or in-plant for your maintenance team.
Interactive Fault Finder
Choose the symptom to see likely causes, what to check next and what to record, then add it to the fault record.
Pick the symptom you see. Always follow plant isolation procedures before inspection.
SINAMICS G120C Fault Codes on the BOP-2: Quick Reference
The codes you will see most often on a G120C, what they mean and where to look in STARTER. F = fault (drive stops, needs acknowledging), A = alarm (warning, drive keeps running).
| BOP-2 code | Meaning | Typical cause | STARTER check / fix |
|---|---|---|---|
| F30001 | Power unit: overcurrent | Short accel ramp, jammed load, motor/cable fault | Trace r0027; p1120; check p0304–p0311; insulation test |
| F07801 | Motor overcurrent | Wrong motor data, overload, short ramp | p0304–p0311, motor ID p1900, p0640 |
| F30002 | Power unit: DC link overvoltage | Regeneration on decel, high supply | p1121, Vdc_max p1240/p1280, braking resistor p0219 |
| A07400 | Vdc_max controller active | Drive is extending decel to protect DC link | Expected; if decel too long, add braking resistor |
| F30003 | Power unit: DC link undervoltage | Supply dip, loose terminal, weak supply | Trace r0026; check p0210 and supply |
| F30011 | Line phase failure in main circuit | Blown fuse, open phase, contactor | Measure all phases; check fuses and contactor |
| F30021 | Power unit: ground fault | Motor/cable insulation | Disconnect drive, megger motor and cable |
| F07900 | Motor blocked | Mechanical jam, wrong control settings | Free the load; check current limit and control mode p1300 |
| F07011 | Motor overtemperature | Overload, low-speed cooling, sensor | r0035; p0335 cooling type; p0601 sensor |
| F30004 | Heat sink overtemperature | Fan, dirty heatsink, ambient, high pulse frequency | r0037; check fan; p1800 |
| F30005 | Power unit overload I²t | Sustained overload | Compare r0027 with drive rating; reduce load |
| F08501 | PROFINET setpoint timeout | Cable, name/IP, PLC stop, watchdog too tight | p8920/p8921, p0922, r2050; PLC watchdog |
| F01910 | Fieldbus setpoint timeout (USS/Modbus) | Bus interrupted, master off, p2040 | p2040; cable, address, baud |
| F07220 | Control by PLC missing | PLC control bit (STW1.10) not set | Check PLC control word and telegram |
| F03505 | Analog input wire break | Open 4–20 mA loop | r0752 raw value; wiring; p0756 = 3 |
Fault texts and parameter numbers vary by firmware. Always open the help for the code in STARTER (or the G120C list manual for your firmware) before replacing hardware. Newer G120C units are commissioned with Startdrive (TIA Portal), and the diagnostics work the same way.
Motor Does Not Start
G120C on BOP-2 (simplified)
- — — — no fault shown
- r0046 missing enables
- r0052 status word
Solution using STARTER
- No fault on the BOP-2 but no rotation? In STARTER open Diagnostics → Control/status words and read
r0046(missing enable signals): it names the exact missing permissive (OFF2, OFF3, STO, enable, etc.). - Check the command source the macro set (
p0015, andp0840for the ON/OFF1 source) against the wiring or fieldbus. - Use the STARTER Control panel (assume control priority) to run the motor from the PC: if it runs, the fault is in the PLC/terminal command path, not the drive.
r0046r0052p0015p0840| Observation | Likely area | Check |
|---|---|---|
| Ready but no run | Command source | Terminal, fieldbus or keypad selection |
| Run active but 0 Hz | Reference source | Analogue, network or fixed speed |
| Drive inhibited | Interlock or safety | STO, enable, permissive |
| Motor hums | Output or motor | Phases, cable, motor connection |
Overcurrent, Overvoltage and Undervoltage: Read the Timing
G120C on BOP-2 (simplified)
- F30001 overcurrent (accel)
- F07801 motor overcurrent
- F30002 DC link overvoltage (decel)
- A07400 Vdc_max controller active
- F30003 DC link undervoltage (dip)
Solution using STARTER
- In STARTER start a Trace on
r0021(speed),r0027(current) andr0026(DC link), triggered on the fault, to see when it trips. - F30001/F07801 on accel: lengthen
p1120, verify motor datap0304–p0311, repeat motor IDp1900, insulation-test the motor and cable with the drive disconnected. - F30002 on decel: lengthen
p1121; use the Vdc_max controller (p1240vector /p1280V/f), or fit a braking resistor and setp0219. - F30003 / F30011: trace
r0026during the event, check thatp0210matches the real supply voltage, and check phases, fuses and terminal torque.
r0021r0027r0026p1120p1121p1900p1240p1280p0219p0210If protection opens repeatedly on power-up, never fit a larger rating. Investigate the rectifier, DC bus, wiring and short-circuit conditions.
Overload and Overheating
G120C on BOP-2 (simplified)
- F07011 motor overtemperature
- F30004 heat sink overtemperature
- F30005 power unit overload I²t
Solution using STARTER
- Monitor
r0035(motor temperature) andr0037(power unit temperatures) in a STARTER trace over a full duty cycle. - Compare load current
r0027with the motor rated currentp0305: continuous current above rating is a mechanical or process problem, not a drive setting. - Set
p0335to the real motor cooling (self-ventilated vs forced) so the thermal model is correct, andp0601if a PTC/KTY is wired. - For F30004 check the drive fan and heatsink; a lower pulse frequency
p1800reduces drive losses.
r0035r0037r0027p0305p0335p0601p1800Also check cooling-fan operation, heatsink contamination, enclosure ventilation, ambient temperature, carrier frequency and motor parameters.
Communication Faults
G120C on BOP-2 (simplified)
- F08501 PROFINET setpoint timeout
- F01910 fieldbus setpoint timeout
- F07220 control by PLC missing
Solution using STARTER
- Read both diagnostics: PLC buffer/topology and the drive Alarms window. Note which side flagged first.
- In STARTER check the PROFINET name
p8920, IPp8921and telegramp0922against the PLC configuration; watchr2050(received PZD) change while online. - For USS/Modbus (F01910) the monitoring time is
p2040; for PROFINET the watchdog comes from the PLC hardware configuration. Size it above the worst-case PLC cycle; never set it to 0 to hide a fault.
p8920p8921p0922r2050p2040Analogue Reference, Noise and Vibration
| Symptom | Check |
|---|---|
| Unstable analogue reference | Signal type, common reference, scaling, grounding; measure vs displayed value; screened cable away from motor cables |
| Motor noise / vibration | Carrier frequency, bearings, alignment, cable length, output reactor, mechanical resonance (skip frequencies) |
| Hot at low speed | Shaft-fan airflow; forced ventilation for continuous low-speed duty |
For analogue scaling see G120 macro 12; to find undocumented parameter changes see STARTER online vs offline comparison.
Hands-On Lab: Diagnose a Planted Fault
Hands-on- '+LABPRE+'
Baseline
On a training drive, run the motor uncoupled and record frequency, current and DC bus voltage at steady speed.
Planted fault 1: short decel ramp
A colleague sets a very short ramp-down time on a high-inertia load (or flywheel).
Planted fault 2: missing permissive
The colleague opens the enable or STO input.
Planted fault 3: wrong command source
The colleague changes the command source.
Fill the fault record
Use the fault record for each planted fault, with one corrective action each.
'+CHECK+'
Frequently asked questions
How do I see the fault history of a G120C in STARTER?
Go online and open the Alarms window, or read the fault buffer in the expert list: r0945 (fault codes), r0949 (fault values) and r0948 (time). Record them before acknowledging.
What is fault F08501 on a G120C?
F08501 is a PROFINET setpoint timeout: the drive stopped receiving cyclic data from the PLC within the watchdog time. Check the cable, PROFINET name p8920, IP p8921 and telegram p0922 against the PLC, and size the watchdog above the PLC cycle rather than disabling it.
What does F30001 or F07801 mean on a G120C?
Both are overcurrent faults, usually during acceleration: a short ramp-up time p1120, wrong motor data p0304–p0311, a jammed load or a motor/cable fault. Trace r0027 in STARTER, correct the motor data, repeat the motor identification and insulation-test the motor with the drive disconnected.
What does F30002 mean on a SINAMICS G120C?
F30002 is a power unit DC link overvoltage, typically during deceleration when the load regenerates energy. In STARTER, trace r0026 and lengthen the ramp-down time p1121, use the Vdc_max controller, or fit a braking resistor and set p0219. Also check that the supply voltage is not high.
Can I reset a VFD fault immediately?
Record the fault code and operating conditions first: frequency, current, DC bus voltage, and whether it was accelerating, steady or decelerating. Reset only when the process is safe and the cause will not create a repeated hazard.
Why does a VFD trip during acceleration?
Usually overcurrent: too short an acceleration ramp, excessive or jammed load, incorrect motor data, or a motor or cable fault. Compare current uncoupled or at reduced load where it is mechanically safe.
Why does a VFD trip during deceleration?
Regenerative energy from the load raises the DC bus voltage until the overvoltage trip. Lengthen the deceleration ramp, enable the DC bus voltage controller, or fit a braking resistor. Also check for high supply voltage.
Can a megger be used on a motor connected to a VFD?
Never test through the drive. Disconnect and isolate the motor from the drive output first, then follow the drive and motor manufacturers’ instructions.
What causes VFD communication loss?
Cable damage, network power, shielding, topology or termination, wrong address or baud rate, telegram mismatch, network load, or a watchdog set tighter than the PLC cycle. Check PLC-side and drive-side diagnostics together.
Why is the motor hot at low speed?
A shaft-mounted fan moves far less air at low speed while torque demand can stay high. Use forced ventilation or an inverter-duty motor for continuous low-speed operation.
Why does the motor not start even though the drive shows no fault?
Walk the permissive chain: drive ready, enable/STO, run command from the selected source, a non-zero reference, and limits that allow running. The first missing link is the cause.
What is the most important troubleshooting habit?
Capture evidence before changing parameters or resetting the fault, change one thing at a time, and record the result.