Troubleshooting SINAMICS S120 F30021 F30025 at Power-Up

Overview

This reference covers the cluster of faults that appears on a SINAMICS S120 drive line-up at the moment of first power-up, in particular the simultaneous presence of a ground-fault event on the Motor Module and a thermal event on the power-unit semiconductors. The cluster is dominated by F30021 (ground fault), F30025 (chip overtemperature), F30004 (heat sink overtemperature), and the supporting F5000 / F5001 sensor faults. An information-class message F7085 (parameter changes, often with parameter 1800 referenced) is usually co-reported because the CU320 reloads non-volatile parameters that differ from the live project.

The reference configuration is a small SLM (Smart Line Module) feeding a Single Motor Module controlled by a CU320 with firmware 2.6 and commissioned through STARTER. The faults are reproducible on every power-up, even with the motor disconnected and no enable signal present. This pattern — fault present with no load and no enable — is the diagnostic signature of a hardware defect inside the inverter section, not a process, motor, or wiring fault.

System Architecture and Affected Components

The SINAMICS S120 is a modular drive system. The CU320 control unit handles closed-loop control, communication (PROFIBUS / PROFINET) and non-volatile parameter storage. The Smart Line Module (SLM) provides unregulated DC-link voltage from a three-phase supply. The Single Motor Module converts the DC link into a variable-frequency output for one motor. All three components are interconnected by DRIVE-CLiQ.

Because every thermal and ground-fault event originates from the same Drive_1 object (the Motor Module), the fault cluster points to one component — not to a system-wide supply or earthing problem. DRIVE-CLiQ cabling and 24 V DC supply must be ruled out only as a secondary cause.

Fault Code Reference Table

The numbers shown in parentheses in the live fault buffer are Siemens fault-value encodings. They are not direct degrees Celsius; they are raw A/D counts reported by the power-unit firmware and decoded by STARTER into the engineering unit on the alarm screen. A fault value of 10859 on F30025 is therefore evidence that the IGBT temperature acquisition path is alive — a useful diagnostic clue.

Symptom Matrix

Root Cause Analysis

Ground Fault — F30021

F30021 is raised by the Motor Module firmware when the sum of the three phase currents deviates from zero beyond the configured leakage threshold, or when the IGBT desaturation monitor trips on a low-side or high-side switch. In a no-motor test on the bench, the only path through which such a current can flow is internal to the Motor Module — either across a phase-to-DC-link insulation weakness, a gate-driver short, or a failed IGBT module.

The reported fault value (e.g. 31220) carries the cycle count and the affected channel. A fault value that survives every ON / OFF cycle and every OFF2 reset is characteristic of an internal short, not an external wiring problem. Resetting the fault with p2102[0] only suppresses the display — it does not clear the underlying defect.

Thermal Cluster — F30025 / F30004 / F5000 / F5001

The thermal cluster is the key fingerprint. When an IGBT is short-circuited internally, the gate-driver pulls the device into a hard-conduction state at the moment of pre-charge. The high dissipation heats the silicon die within milliseconds, long before the heat sink sensor can register the rise. The firmware logs both events:

1. F30025 — chip overtemperature — typically fires within a few hundred milliseconds of DC-link energisation if the IGBT has failed short or has a gate-source short.
2. F30004 — heat sink overtemperature — fires once the heat sink itself warms up.
3. F5000 / F5001 — sensor faults — are often co-reported because the firmware reads the thermal A/D converters during the same event.

In other words, the thermal faults are downstream effects of the same root failure: a defective Motor Module. Treating them as independent cooling or fan issues is a common field error and delays the swap-out by hours.

Parameter Change Information — F7085

F7085 is an information message, not a fault. It is raised when the parameter values held in RAM differ from the values stored to ROM, typically because the project on the engineering PC differs from the data last saved on the CU320, or because parameter 1800 (PWM frequency) has been adjusted at runtime. With FW 2.6, the default p1800 is 4 kHz. If the offline project requests 8 kHz or 16 kHz, F7085 fires to signal the mismatch and the drive continues to run at the RAM value until acknowledged.

F7085 does not need to be cleared before the drive can run, but it should be investigated because it usually signals that the project on the PG and the data on the CU320 have drifted apart. The resolution is to download the offline project and save RAM to ROM.

Pre-Diagnostic Checks Before Component Swap

Before condemning the Motor Module, perform four checks that resolve a meaningful fraction of similar fault clusters in the field.

24 V DC Control Supply

The CU320 and the DRIVE-CLiQ ports are powered from an external 24 V supply (typically a Siemens SITOP PSU from the 6EP1 family). Measure the rail at the CU320 terminals with the line infeed energised, looking for:

• Voltage drop below 21 V during pre-charge — indicates that the PSU is undersized for the inrush of the Motor Module fans and contactors.
• Ripple > 200 mV peak-to-peak — indicates a noisy or overloaded supply that can corrupt DRIVE-CLiQ communications.
• Reverse polarity — many SINAMICS components survive reverse polarity briefly but log random faults on power-up.

A clean 24 V rail measured between CU320 terminal X124 (24 V) and terminal X124 (M) is the prerequisite for any further diagnosis.

Earthing Concept

The protective earth (PE), functional earth (FE) and 24 V common (M) must be referenced to a single star point. A common field fault is to bond the cabinet PE to the building earth at two points, creating a ground loop that biases the Motor Module current sensors. Measure the resistance between cabinet PE and the Motor Module heat-sink stud — it must be below 1 Ω with no measurable AC voltage between them.

DRIVE-CLiQ Topology

Verify that the DRIVE-CLiQ cables are connected as the firmware expects. With FW 2.6 on the CU320, the auto-configuration expects the SLM on port X100 of the CU320 and the Motor Module on the next available port. A swapped cable will cause the Motor Module to be identified as the SLM and vice versa, leading to cascading faults including F30021 because the wrong DC-link monitoring parameters are loaded. Inspect each DRIVE-CLiQ connector for crushed insulation at the boot — a frequent issue after cabinet transport.

Ambient and Cooling

Even though the cluster appears at power-up with no load, an ambient temperature above 45 °C combined with a failed internal fan can cause F30004 to trip. Check that the internal fan of the Motor Module is rotating freely and that the cabinet inlet air is within the SINAMICS S120 operating range (0 … 45 °C without derating, up to 55 °C with derating per the S120 equipment manual).

STARTER-Based Diagnostics

Reading the MLFB and Firmware

Each SINAMICS component reports its machine-readable order code (MLFB) on power-up. In STARTER:

1. Go online with the CU320 over PROFIBUS or PROFINET.
2. Open the drive navigation tree.
3. Right-click the affected Drive_1 → Overview → Versions.
4. Read the Order No. (MLFB) and the firmware versions of the Control Unit, the Power Unit, and the Safety Integrated module if present.

Record the firmware version of the Motor Module and the CU320. With FW 2.6 components, do not mix with FW 4.x or 5.x components — SINAMICS S120 firmware versions must be matched at the line-up level. A mixed line-up can produce spurious F30021 events on first power-up because the parameter signatures between CU320 and Motor Module do not agree.

Live Fault Buffer

The fault buffer is accessible from the navigation tree under Diagnostics → Fault buffer / Alarm buffer. Each entry shows the fault number, the time stamp relative to power-on, the fault value (the number in parentheses), and the acknowledgement status. Note whether the faults clear after a POWER ON reset or whether they reappear on every cycle. A fault that reappears within two seconds of DC-link energisation is a hardware signature.

Diagnostic Parameter Quick Reference

Resolution Procedure

The recommended resolution sequence, based on the symptom pattern in this reference.

Step 1 — Capture Baseline

1. Power down the cabinet and lock out the line infeed using a visible-break disconnect.
2. Wait five minutes for the DC link to discharge. Measure with a CAT III 600 V meter between DCP and DCN on the Motor Module.
3. Connect STARTER via PROFIBUS or PROFINET.
4. Power the 24 V rail only (line infeed still OFF).
5. Go online with the CU320 and read the MLFB and firmware versions from the Versions tab.
6. Export the project and the fault buffer to the engineering PC.

Step 2 — Factory Reset of the CU320

1. In STARTER, navigate to the CU320 node.
2. Right-click → Target device → Restore factory settings.
3. Confirm. The CU320 will reset all parameters to their defaults and delete any project-specific configuration stored on the CompactFlash card.

This step clears any locally stored parameter drift that may be the source of F7085, and ensures that the next commissioning starts from a known state.

Step 3 — Automatic Commissioning

1. Run Automatic commissioning on the affected drive (Drive_1).
2. STARTER will re-detect all DRIVE-CLiQ components and re-load the default power-unit parameters from the firmware image.
3. Accept the online / offline comparison screen and download to the target.
4. Save RAM to ROM (Copy RAM to ROM) so that the new state survives the next power cycle.

Step 4 — Re-test Without Motor

1. Disconnect the motor cables from the Motor Module terminals U2, V2, W2.
2. Power up the cabinet (line infeed ON).
3. Observe the fault buffer on the CU320 within ten seconds.

If F30021, F30025 and F30004 reappear within two seconds and the Motor Module is isolated from any external wiring, the Motor Module itself is defective and must be replaced. The motor cables are not in the circuit, so no external leakage path exists.

Step 5 — Hardware Swap Test

1. Power down and lock out. Wait five minutes for DC-link discharge.
2. Replace the Motor Module with a known-good unit of the same MLFB and the same or compatible firmware.
3. Re-run automatic commissioning on the swapped unit.
4. Power up and observe the fault buffer.

If the fault cluster does not reappear on the swapped unit, the original Motor Module is the failure source. Send it to an authorised Siemens repair centre and quote the fault value from F30021 to expedite triage.

Parameter Adjustments That Do Not Fix This Cluster

Three parameters are often offered as workarounds for thermal faults. They do not fix this cluster and should not be relied upon.

Adjusting p0290, p0291 or p0294 may temporarily move the faults to warnings, but the drive will not operate reliably until the underlying hardware defect is resolved. Use these parameters for thermal margin tuning on healthy drives, not as a fix for F30021.

Hardware Swap and Verification

When swapping the Motor Module, observe these rules:

• Match the MLFB exactly — a Booksize Single Motor Module 6SL3120-xTE21-xAAx is not equivalent to a 6SL3120-xTE21-xABx in firmware defaults.
• Match the firmware version using the CU320's web server or the SD card's stored image.
• Re-validate the Safety Integrated parameters if the original drive was safety-enabled — DI Enable on port X131 must be re-wired and re-commissioned.
• Re-torque the DC-link busbar and the PE stud to the torque specified on the unit label.

After the swap, run a no-load test, then a motor identification run (p1910), then a closed-loop commissioning check before returning the drive to production.

Verification Checklist

Field-Proven Caveats

• F30021 on FW 2.6 may also be raised by a damaged DRIVE-CLiQ cable between the SLM and the Motor Module. Inspect the cable for crushed insulation at the connector boot before swapping the Motor Module.
• If the cabinet has been transported or relocated, a cracked solder joint on a power-module gate-driver PCB can produce exactly this fault pattern. Visual inspection under magnification is required before condemning the module.
• Do not attempt to clear F30021 by entering the fault value in p2102 — that approach masks the diagnostic and has caused field downtime.
• F7085 alone, without F30021, is not a defect — it is a project / device mismatch that can be resolved by saving RAM to ROM after the offline project has been downloaded.
• Replacing the Motor Module without first disconnecting the motor cables can produce misleading test results because an external ground fault will still be present.
• FW 2.6 is end-of-life and Siemens recommends migration to FW 4.x or 5.x where compatible. Mixed firmware versions in the same line-up are not supported and should be reported to the support organisation, not patched in the field.

Related Official Documentation

• Siemens Industry Online Support — fault-code search
• SINAMICS S120 product family page

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