Resolving Siemens Sinamics F30021 Ground Fault During Motor ID Stationary Measurement

The F30021 fault on a Siemens SINAMICS drive is one of the most disruptive alarms an integrator can encounter during commissioning. It typically surfaces during the stationary motor identification (motor ID) routine, sometimes within the first 200–500 ms of the pulse pattern being injected into the stator. The drive measures a current that exceeds the configured ground-fault monitoring threshold and immediately trips, halting the identification run and locking out the inverter until the cause is cleared. The root cause is rarely a single catastrophic insulation failure; in most field cases the trip is triggered by the combination of long motor cable capacitance, switching transients at the high PWM frequency, modest phase-to-ground insulation asymmetry, and an overly sensitive monitoring threshold.

This article gives a field-proven diagnostic sequence: from insulation and IGBT sanity checks, through interpreting the alarm value buffer (r0949) and current unbalance (p287[1]/p0287[1]), to the parameter changes and wiring corrections that reliably clear the fault on SINAMICS S120, G120, G130/G150, S150, and V90 platforms.

1. F30021 Fault Definition and Reaction

F30021 is signalled by the Sensor Module / Motor Module firmware and is mapped to fault class ground fault detected. The reaction is configurable but defaults to OFF2 (p2100, p2101 mapping) so the drive pulses are removed and the line contactor is dropped on the next base block. The fault must be acknowledged (acknowledge fault via p3981 = 1 or via the control word STW1 bit 7) before the drive can be re-enabled.

2. Why F30021 Trips During Stationary Motor ID

The stationary motor identification routine applies a defined current pattern at low fundamental frequency (typically 0 Hz) into the stator windings. Because no mechanical rotation is commanded, the firmware treats any measured current that does not return through the expected line-side path as a ground fault. Three physical mechanisms are responsible for the trip in the vast majority of field cases:

1. Real insulation breakdown - phase-to-phase or phase-to-ground resistance below ~1 MΩ under DC test, or breakdown at the elevated dV/dt produced by the inverter's IGBT module.
2. Stray capacitance discharge - the screen-to-ground capacitance of a long shielded motor cable, combined with a high PWM frequency, presents a low impedance path for the high-frequency leakage current. SINAMICS typically switches at 4 kHz (default p1800) but can be raised to 8, 12, or 16 kHz in p1800, dramatically increasing the capacitive current.
3. Current unbalance exceeding p0287[1] - if the difference between the three measured phase currents during the ID pulse exceeds the configured threshold, the firmware declares a ground fault. The threshold is expressed as a percentage of the Motor Module rated current (r0207[1]).

The original report (10 MΩ phase-to-ground with a hand-held multimeter, no fault at p1272 = 1 simulation) and the 37 V AC measurement from phase to ground with the motor disconnected are classic signatures of mechanism (2) and/or (3): the DC insulation is sound, but the AC behaviour is not.

3. Pre-Diagnostic Data Capture

Before powering down or modifying wiring, capture the following so the firmware context is preserved. Use a PG/PC with STARTER, Startdrive, or TIA Portal V17+ connected to the drive via PROFIBUS, PROFINET, or USB.

1. Read r0949[0..7] and the associated r0947[0..63] fault time stamps. F30021 with value 0 indicates a generic ground fault; non-zero values identify the specific Sensor Module or Motor Module that detected it.
2. Read r2131[0..63] for the current alarm word; the F30021 trip is often preceded by A30021 or A05011 (overcurrent warning) when the leakage path is high.
3. Read p0287[0..n] and p0288 to confirm the threshold and delay currently in force.
4. Read p1800 (pulse frequency), p0221 / p0222 (motor cable cross-section and length) and the line-side p0210 (line voltage).
5. Save the project offline and, if the drive is fitted with a CF card, copy /user/sinamics/ for forensic reference.

4. Insulation and IGBT Sanity Check

Even when the multimeter shows 10 MΩ on each phase, the measurement is a 9 V DC check. Re-test with a 500 V or 1000 V megohmmeter to expose insulation that breaks down at the actual dV/dt produced by the inverter (a 400 V SINAMICS IGBT switching at 4 kHz produces edges of 5–8 kV/µs, so a real breakdown is only visible under stress).

With the motor disconnected, set p1272 = 1 to enable simulation. Apply a 50 rpm speed setpoint and observe r0027 (actual current) and r0061 (speed actual). The original post confirms that under simulation the drive runs without F30021, which proves:

• the Sensor Module, Control Unit, and gate-driver paths are functional,
• no internal short exists on the DC bus or in the IGBT module's power section,
• the ground-fault detection firmware is alive and waiting for a real current path.

If a 37 V AC reading appears from each output phase to ground with the motor disconnected and the drive in simulation, this is normal: the IGBT module contains an output filter (Y-capacitors) referenced to PE to suppress common-mode emissions. The voltage is a 50/60 Hz common-mode artefact of the simulated PWM, not a sign of insulation failure.

5. Cable Capacitance and PWM Frequency

A typical 4-core 1.5 mm² shielded motor cable exhibits a screen-to-ground capacitance of 0.4–0.6 nF/m. A 100 m run therefore presents ~50 nF, which at 4 kHz equates to an impedance of:

Zc = 1 / (2 × π × f × C) = 1 / (2 × 3.1416 × 4000 × 50e-9) ≈ 796 Ω

The leakage current through this path is small in steady state, but during a motor-ID pulse the dV/dt is unfiltered and the transient can charge the cable capacitance to the rail voltage. If the cable screen is bonded at both ends and the drive and motor grounds are at slightly different potentials, additional common-mode current circulates. The cumulative leakage can exceed p0287[1] in a single pulse, generating F30021.

6. Current Unbalance Threshold (p287[1] / p0287[1])

The ground-fault monitor does not actually measure insulation resistance directly; it computes a residual sum of the three phase currents. When the absolute value of this residual exceeds the configured percentage of r0207[1] (Motor Module rated current) for longer than p0288 seconds, F30021 is raised.

For a 400 V 200 kW Motor Module (6SL3320-1TE33-1AA3) with r0207[1] = 480 A, the default 5 % threshold is 24 A. During stationary ID, a typical 50 Hz leakage through 100 m of cable and a sine filter can reach 12–18 A, leaving very little margin. Raising p0287[1] to 20 % (96 A) typically clears the nuisance trip without compromising the safety function, because a real insulation breakdown (> 1 MΩ drop) produces hundreds of amps of residual.

7. Wiring and Grounding Mistakes

One contributor in the field is a common Neutral-Earth bond inside a control transformer feeding the drive's 24 V control supply or the fan circuit. If the 0 V / N / PE of a 400/230 V control transformer secondary is shorted to PE at the transformer itself, and then the drive cabinet is also bonded to PE at the cabinet ground bar, the parallel ground loop returns through the drive's IGBT heat-sink Y-capacitors. That current is read by the firmware as a ground fault and trips F30021 during the ID pulse, even on a perfectly good motor and cable.

Fix: keep the control transformer's secondary 0 V referenced to N (not to PE) and let the cabinet PE bar carry the protective earth only. Provide a single, low-impedance bonding point from the Motor Module ground stud to the cabinet PE bar using a 35 mm² or 50 mm² conductor, and from the cabinet PE bar to the plant ground ring with a conductor whose impedance is < 0.1 Ω at 50 Hz.

8. Motor Cable Phase Order and Encoder Direction

The stationary ID itself does not require rotation, so encoder direction only matters for the rotating ID (p1900 = 2 or 3). However, if the operator is running rotating ID and hearing a loud banging or chattering from the motor, the most common cause is reversed motor phase order or reversed encoder polarity. Confirm the wiring:

1. Motor terminal box: U → U1, V → V1, W → W1 (star or delta as per p0300, p0304).
2. Encoder connector: pin A → A, pin B → B, pin Z (or R) → Z. Swap A and B to reverse direction (r0061 negative) without rewiring the resolver or SSI encoder mechanically.
3. Verify with p1300 = 0 and a small setpoint (e.g. 50 rpm) before re-running p1910.

9. Step-by-Step Resolution Procedure

1. Isolate the drive - open the line contactor, wait for DC-link discharge (typically 5 minutes; verify with r0046.0 = 1 / DC bus < 50 V).
2. Megger the motor and cable at 500 V DC phase-to-phase and phase-to-ground; reject if any reading is below Table 2 limits.
3. Inspect the motor terminal box for copper dust, moisture, oil ingress, and correct star/delta jumper position. Clean and re-torque to the manufacturer's Nm (e.g. M10 studs on a 1LE100 frame ≈ 25 Nm).
4. Re-bond the screen at the drive end and the motor end, 360° EMC glands at both, with the screen stripped back only as far as necessary to fit the gland.
5. Confirm clean control-transformer grounding - separate 0 V, N, and PE at the secondary; no jumper between N and PE at the transformer.
6. Reduce the switching frequency for the ID run - set p1800 = 2 kHz temporarily, run the stationary ID (p1910 = 1 + ON), then restore the application PWM frequency.
7. Raise the ground-fault threshold if necessary - p0287[1] = 20 (20 %), and increase the delay p0288 = 2.0 s to ride through the ID pulse transients.
8. Re-run the identification with motor connected, p1272 = 0, p1910 = 1, then issue ON. Watch r0027, r0029, r0061 and the alarm buffer r2122 for A30021 or A05011.
9. Save to ROM - p0977 = 1 (or copy RAM to ROM via STARTER / Startdrive).
10. Run rotating ID if required by the application (p1900 = 2 or 3) and verify encoder polarity by watching r0061 track the setpoint r0062 with the correct sign.

10. Parameter Reference Summary

11. Verification Checklist

After applying the changes above, perform the following to confirm the F30021 is resolved and the motor ID has produced valid parameters:

• r0047[0] reaches 33 (Operation enabled) and stays stable for at least 30 s.
• r0027 (current actual) settles to a steady value of 20–60 % of r0207[1] during the ID pulse and drops to < 5 % after completion.
• r0345 (stator resistance identified) is within ±10 % of the nameplate R-value: R_nameplate = V_phase / (sqrt(3) × I_nameplate) × (1 / 2) for a star motor (factor 1/2 for cold-to-warm).
• r1910 (identified stator leakage reactance) is non-zero and physically reasonable (typically 0.05–0.20 pu).
• The fault buffer r0949[0..7] is empty after acknowledgement and a 10-minute idle run.
• If rotating ID is performed, the motor runs smoothly up to the configured p2000 reference speed, and r0061 matches r0062 in sign and magnitude.

12. Field Notes and Edge Cases

On SINAMICS V90 servo drives, the equivalent fault is F30021 but the parameter to adjust is p0287 (single index only). The V90 has a fixed 8 kHz pulse frequency, so the sine filter (6SL3202-0AE31-1CA0) is the more common remediation. On G120 with CU240E-2 and Power Module PM240-2, the firmware is V4.7 SP10 or newer; confirm the parameter list in the active DCC / IOP / Startdrive project before changing p0287, as the parameter number changed between V4.4 and V4.7. On S150 active line modules, F30021 can also be raised by the line filter, particularly when a clean-power filter is fitted and the cabinet PE is not bonded directly to the plant ground.

Another edge case is the use of sine-wave filters on multi-motor topologies: if several Motor Modules share a common DC bus and a single motor is identified, the residual sum of the unpowered motor modules' capacitive currents can add to the residual of the active module. Run the ID on each Motor Module with the others disabled in p0105 to avoid this.

Finally, on retrofits where the original drive was an older MASTERDRIVES or SIMOVERT, the motor cable may be unshielded and routed in the same tray as the 24 V control wiring. The capacitive coupling from the 24 V pairs to the U/V/W cores during the ID pulse can present a ~30 V common-mode signal that the firmware misreads. In this case, separate the trays by at least 200 mm and use a shielded motor cable.

13. FAQ