Resolving SINAMICS G120 F30022 Fault on PM240 FSGX Boot

Problem Overview

The SINAMICS G120 drive system built around a PM240 Power Module, MLFB 6SL3224-0XE41-6UA0 (frame size FSGX) and a CU 240E-2 DP Control Unit, MLFB 6SL3244-0BB12-1PA1 on firmware V4.5 reports F30022 immediately after power-up whenever an external DC 24 V control supply is fed to the Control Unit terminals while the three-phase 400 V line is not yet connected to the Power Module. The drive refuses to transition to operating readiness (state READY) and the control electronics on the Power Module side remain unpowered. When the line is applied first and the Control Unit's external 24 V is added afterwards, the fault does not appear.

This is a Power Module hardware-supply issue, not a CU firmware bug and not a PROFIBUS problem. The behavior is fully explained by the fact that PM240 FSGX Power Modules route their internal control-electronics 24 V from a dedicated, externally fed input on the Power Module itself — not from the line-rectified DC link — and that the CU cannot close the internal handshake with the Power Module until that input is present.

Identifying the Hardware: PM240 FSGX

The PM240 is the basic (non-regenerative) Power Module for the SINAMICS G120 chassis range. It is offered in frame sizes FSA through FSGX. The FSGX variant is mechanically and electrically different from the smaller frames in one critical respect: the internal control electronics of the Power Module require an independent DC 24 V supply that is not generated from the DC link.

This is documented in the SINAMICS G120 PM240 Operating Instructions and the G120 Function Manual. The reason is that FSGX uses an intelligent line contactor / pre-charging topology where the contactor coil and the gate-drive / IGBT-driving electronics of the rectifier section must be energized before the DC link capacitors can charge through the pre-charge resistors. On smaller frames (FSA–FSF) this auxiliary 24 V is derived internally from the DC link via an auxiliary power supply that can self-bootstrap once the link charges. On FSGX there is no internal bootstrap, so a clean external 24 V is mandatory whenever any CU is mounted.

Fault Code Anatomy: F30022 and r0949 = 7

F30022 belongs to the SINAMICS fault class Power Unit. The message text is "Power unit: DC link voltage monitoring". The drive continuously samples the DC link voltage (parameter r0070) and compares it against the undervoltage threshold derived from the parameterized line voltage (p0210). When the sampled value is below the threshold for longer than the debounce time (typically 1–3 line cycles, dependent on p0210/p0280 settings), F30022 is raised.

The fault value r0949 disambiguates the cause. Common values seen in G120 installations include:

The reported r0949 = 7 in this fan application is the canonical signature of "DC link voltage not established within the expected window after power-on because the Power Module's internal logic supply is missing." The CU is awake (because its own 24 V terminal is fed), but the PM cannot answer the handshake because its own 24 V rail is dead.

Root Cause Analysis

The control architecture of a G120 separates the 24 V domain into three islands:

1. CU 24 V domain — fed through the Control Unit terminals (on CU240E-2 DP these are the removable two-position terminal block at the front: 24V and M). When fed, the CU boots regardless of line state.
2. PM internal 24 V domain — fed on PM240 FSGX from terminal block -X9 on the Power Module itself: P 24 V (terminal 1) and Mext (terminal 2).
3. DC link 24 V domain — derived on smaller frames from the rectified mains via an internal auxiliary SMPS; on FSGX, this domain is only energized after the PM internal 24 V is present and the pre-charge contactor is commanded closed.

The DRIVE-CLiQ / PM-CU handshake runs once the CU comes out of reset. The CU asks the PM for its identification (PM order number, rated current, firmware version). The PM's response is generated by its internal logic, which is dead without -X9 supply. The CU therefore reads "PM not responding", infers that the DC link cannot have been pre-charged (because no PM electronics ran the pre-charge sequence), and trips F30022 / r0949 = 7.

This is precisely the diagnostic logic described in the SINAMICS G120 List Manual and reproduced in the PM240 Operating Instructions under the section "Connecting the external 24 V supply (FSGX only)".

Terminal Block -X9 on the PM240 FSGX

Locate the small Phoenix-style two-position terminal block marked -X9 on the front face of the Power Module, immediately to the right of the PM-CU ribbon-cable connector. Terminal assignments:

Typical consumption is 0.8 – 1.5 A on FSGX, so the external 24 V source must be sized for the worst-case sum of CU consumption (≈0.5 A for CU240E-2 DP) plus this 0.8 – 1.5 A plus headroom for inrush. A 5 A DIN-rail supply (e.g. Siemens 6EP1334-3BA10 SITOP PSU100S or equivalent) is the typical field choice.

Wiring Topology (Inline SVG)

The diagram below shows the corrected power-up topology for a G120 with PM240 FSGX, CU240E-2 DP, and external 24 V feeds to both the CU and the Power Module. The CU's 24 V and the PM's 24 V should be sourced from the same regulated DC supply so they rise and fall together.

Step-by-Step Resolution

Use the procedure below to convert a G120 with PM240 FSGX from a configuration that faults on cold boot to a configuration that powers up cleanly with the Control Unit pre-energized.

Step 1 — Confirm the frame size and MLFB

1. Open the cabinet door and read the MLFB label on the Power Module. Confirm it is 6SL3224-0XE41-6UA0 or another FSGX variant (the suffix letter after the current rating is "X" for FSGX).
2. Cross-check with the printed frame-size diagram inside the PM240 Operating Instructions. FSGX has a distinct enclosure footprint compared with FSG.

Step 2 — Locate terminal block -X9 on the Power Module

1. On FSGX, -X9 is a removable two-position Phoenix MSTB 2,5-style terminal, located on the front of the Power Module near the bottom-left of the PM face.
2. Verify the marking silk-screen on the PM body reads -X9 with pin numbering 1 P24V and 2 Mext. Do not confuse with the customer's -X1 / -X2 mains terminals.

Step 3 — Wire a regulated 24 V source to -X9

1. Run a twisted pair (≤ 1.5 mm², ≤ 10 m) from the +24 V rail of an existing cabinet-mounted 24 VDC PSU (or add a dedicated one) to terminals 1 and 2 of -X9.
2. Maintain the same 0 V reference between this supply and the Control Unit's 24 V supply. If the two supplies are separate, bridge their 0 V rails with a dedicated bonding conductor.
3. Do not route the 24 V cable in the same conduit as the motor output leads (U/V/W); keep ≥ 200 mm separation to avoid induced noise on the gate-drive reference.

Step 4 — Power-up sequence check

1. With 400 V line disconnected, energize only the external 24 V to both the CU and -X9. The CU should boot to READY within 4–6 seconds, the PM should report its identification in r0002 / r0200, and the DC link voltage r0070 should remain at 0 V (line not present). No F30022 should be raised.
2. Apply the 400 V line. The PM's internal pre-charge contactor closes, the DC link rises to ≈540 V DC, and r0070 / r0026 update. The drive transitions through PRE-CHARGING to READY.
3. Issue the ON command from the PROFIBUS master. The inverter runs the fan.

Step 5 — Acknowledge and clear any historical fault buffer entries

1. If F30022 is still latched from prior incorrect wiring, acknowledge it via p3981 = 1 on the CU (or pulse bit STW.7 from the PROFIBUS master).
2. Inspect the fault history (r0947[0..7]) to confirm the r0949 value is no longer 7. If a different value appears (e.g. 2), investigate mains stability separately.

Verification Procedure

Once the wiring is corrected, the following checks prove the installation is sound:

Related Faults and Cross-References

F30022 is one of a small family of faults that all point at the PM-CU 24 V / DC link handshake. If F30022 persists after wiring -X9 correctly, work through the adjacent fault set:

Parameter Reference

Key parameters when commissioning or diagnosing this issue on the CU240E-2 DP:

Why the Fault Appears Only on Cold Boot With 24 V First

The CU is on the same 24 V domain as the user's external supply, so it boots immediately. The PM's logic supply, however, is fed by -X9 only. When the user energizes 24 V first and the 400 V line is not yet present, the CU performs its initialization sweep and queries the PM over the PM-CU ribbon. The PM does not respond because its own 24 V rail is missing on FSGX. The CU interprets the silent PM as "DC link not pre-charged" and raises F30022 / r0949 = 7.

On smaller frames (FSA–FSF) the situation does not arise because the PM has an internal auxiliary supply that bootstraps from the DC link once the rectifier charges it, and on those frames the user can pre-power the CU and the PM will start talking back as soon as the DC link is up.

Alternative: Run CU Without External 24 V

Some plant designs intentionally avoid feeding the CU with external 24 V so that the drive is fully off when the 400 V is open. In those designs the DCS must tolerate the PROFIBUS node dropping in and out. If that is acceptable for the process, omit the external 24 V feed to the CU and instead derive the "drive is alive" indication from a separate contactor or a digital input wired to a control relay on the 400 V line. This avoids the F30022 issue entirely because the CU powers up together with the line.

If, however, the process requires the drive to be visible on PROFIBUS at all times for diagnostics and parameter access, the only correct fix is to feed both the CU and -X9 on the PM240 FSGX.

Commissioning Checklist for Fan Applications

1. Confirm line voltage on the 400 V side matches p0210 (400 V).
2. Verify p0100 = 0 (50 Hz / IEC).
3. Set p1300 = 0 (V/f linear) or p1300 = 1 (V/f quadratic) for fan load; quadratic is usually the better efficiency choice for fans.
4. Set ramp times p1120 / p1121 to match fan inertia. Typical values: 30 s / 45 s for a 18.5 kW axial fan.
5. Configure the PROFIBUS telegram to a standard PPO type 1 (PZD 2/2) or Siemens telegram 1 (PZD 2/2). Map control word 1 (STW1) and status word 1 (ZSW1).
6. Set p2051[0] = r2089[0] (ZSW1 to PZD1) and p2051[1] = r2089[1] (ZSW2 to PZD2) for the receive direction.
7. After wiring -X9, perform a controlled power-down and power-up with only the 24 V present to confirm F30022 does not appear.
8. Apply line, run a no-load ramp to confirm direction and speed feedback, then connect to the mechanical load.

Field-Proven Caveats

• Some early PM240 FSGX units (produced before mid-2014) used a different -X9 pinout. Always confirm against the wiring diagram shipped with the specific unit, not against the generic manual.
• If the 24 V supply to -X9 is shared with other loads and the supply sags under load (inrush from contactors, solenoids, etc.), F30022 may reappear intermittently with r0949 = 2 instead of 7. Use a dedicated 24 V rail for the drive.
• The PM-CU ribbon cable is keyed; do not force. A bent pin on the cable connector produces F30662 instead of F30022, so the fault signature alone distinguishes the root cause.
• When replacing a PM240 FSGX in the field, record the existing p0210 / p1300 / p1120 / p1121 from the old CU via STARTER or BOP-2 (parameters in PS0031xx memory card backup) and restore them after the swap. A fresh parameter set with default p0210 = 480 V will mask itself as an F30022 on a 400 V line.

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