Siemens SINAMICS G120 F30011 Fault — Phase Loss Fix

Quick answer

SINAMICS G120 F30011 (Line Phase Loss) means the Power Module’s input phase-monitoring logic detected that one of the three input phases is missing or severely sagged for longer than the configured debounce time. Ninety percent of these are real — blown branch fuse, open disconnect pole, broken conductor at a lug, or a tripped upstream protection clearing one phase. The other ten percent are configuration: drive is fed from a single-phase derated supply but the firmware is configured for three-phase, or a phase-monitoring debounce window is set unreasonably tight.

What F30011 means

The G120 doesn’t directly measure each input phase voltage — it measures the resulting DC bus ripple. A healthy three-phase rectifier produces a 6-pulse ripple on the DC bus with a specific frequency (6× line frequency, so 360 Hz on a 60 Hz line). When one phase is missing, the bus ripple changes character — the frequency drops, the ripple amplitude increases, and the average bus voltage sags. The firmware detects this signature change and posts F30011.

The debounce window is configured by p0291 Power Module config and related parameters. By default the firmware waits long enough (typically 100–500 ms) that a one-cycle line glitch won’t trip the fault. Sustained phase loss does.

F30011 is a different fault than F30003 (DC link undervoltage), though they can occur together. F30011 specifically identifies phase loss as the cause; F30003 just identifies that bus voltage dropped below threshold. On a single-phased input you may see both — F30011 first (detected by ripple signature), then F30003 (as the bus collapses).

The fault is significant because running on two phases will eventually destroy the input diode bridge (single-phasing nearly doubles the current through the remaining two phases) and overheats the DC bus capacitors. The drive trips to protect itself.

Read the fault history first

This is the step that separates a 20-minute diagnosis from a parts swap. Do not clear the fault before you read the history.

Open STARTER or TIA Portal with Startdrive. Connect via PROFINET or USB. Drive object → Diagnostics → Faults and alarms.

Capture:

• r0945 F30011 entries
• r0948 timestamps — phase loss events often correlate with weather, time of day (cooling tower starts), or specific neighbor activity
• r0949 — supplemental fault value, encodes which phase signature was detected as missing
• r0026 — current DC link voltage
• r2122 — alarm history, look for A30016 (input voltage out of tolerance) preceding the fault

Field insight on F30011: the r0949 value often tells you which phase. The detection is via ripple signature, so the firmware estimates which phase is missing based on the ripple pattern — it’s not always perfect, but a consistent r0949 value across multiple events points to a specific phase failure. Walk that phase’s path from the drive lug back to the upstream disconnect.

Common causes (ranked by frequency)

1. Blown branch fuse on one phase — fuse cleared on overcurrent, ground fault, or simple end-of-life. Most common F30011 cause.
2. Loose terminal on one input phase — lug not torqued to spec or backed off over thermal cycling. The connection becomes high-impedance under load.
3. Open contactor pole or disconnect contact — upstream switching gear with one pole that’s no longer making contact.
4. Broken conductor at a connector or splice — wire failure inside the panel or out in the conduit. Sometimes invisible — the wire looks intact but a strand-by-strand break has dropped current capacity.
5. Utility phase loss — utility transformer lost a primary fuse, drive sees the resulting secondary phase loss. Rare in commercial settings but happens.
6. Single-phase supply with three-phase configuration — drive is being fed single-phase (typical only for very small G120 ratings) but parameterized for three-phase. F30011 fires on every power-up.
7. Failed phase-monitoring relay or false trip — extremely rare on G120; the monitoring is firmware-based, not via a separate relay. Almost never the cause.

Step-by-step diagnosis

Before you touch anything: lock and tag the disconnect, wait 5 minutes for DC link discharge, verify zero voltage at the DC link terminals with a CAT-IV meter.

1. Read r0945, r0949 before clearing. Note the phase indicated by r0949 and any precedent A30016 alarms.

2. Verify the input fuses. Power off, remove each input fuse, check continuity with a meter. Replace any open fuse — but find out why it opened before re-energizing. A fuse that cleared has a reason.

3. Check terminal torque at every input lug. Calibrated torque screwdriver, published spec on the cover label. Look for discoloration (heat-stressed connection), melted insulation around the lug, and any sign of arcing.

4. Meter input voltage at the drive terminals — with the drive de-energized and locked. L1-L2, L2-L3, L3-L1. With supply restored upstream (drive still locked out), each pair should read three-phase voltage within ±10% of nominal. A single low reading on one pair points to the missing phase.

5. Trace the missing phase upstream. From the drive input terminal, follow that phase back through every connection point: branch disconnect, distribution panel breaker, MCC bucket, utility transformer secondary. The break is somewhere in that path.

6. Verify single-phase vs. three-phase configuration. If your drive is small enough for single-phase operation (typical limit is around 4 kW on G120 with appropriate part number), confirm p0205 Application input phases (or the relevant parameter for your Control Unit firmware revision) matches your supply. A three-phase drive being fed single-phase is misconfigured and will F30011 every time.

7. Inspect upstream switching gear. Open every disconnect and contactor between the drive and the utility entrance. Look for: welded contacts, burned arc chutes, broken pole shafts, evidence of arcing across an open pole. A worn motor disconnect with one pole that doesn’t fully close on closure is a common F30011 source.

8. Set up a power quality logger. If standing measurements are clean and the F30011 is intermittent, install a Fluke 1748 on the drive input for 7 days. Look for momentary phase dropouts during specific events (compressor start, large fault clearing).

Field knowledge nugget: On Siemens G120 drives installed in older industrial facilities with 480V delta supplies and split-bolt taps in the main panel, F30011 trips that appear after years of trouble-free operation are almost always a corroded split-bolt connection deep in the distribution wiring, not a drive problem. The split-bolt sits in a J-box or panel where moisture and dissimilar-metal corrosion (aluminum branch wire to copper main bus) slowly increases the joint resistance. The joint gets hot under load, oxidizes faster, and one day it opens entirely. I traced a chronic F30011 problem at a New Jersey chemical plant to a split-bolt buried in a 25-year-old MCC bucket — the connection had gone from milliohms to over an ohm under load. Heat-thermography is your friend on this; an FLIR scan of distribution gear under load will catch this hours before it becomes a fault.

Parts that may need replacement

When to call Siemens, an electrician, or a controls engineer

Call a licensed industrial electrician immediately if: the missing phase is not obviously a fuse or terminal issue and the trace points to utility-side or main distribution gear; you see evidence of arc-flash damage in any switching equipment; or the fault correlates with utility transformer activity. Call a controls engineer for: F30011s that persist after all upstream electrical has been verified good (suggests internal drive issue); coordinated multi-drive systems where a single phase event is affecting multiple drives differently; or applications where the phase-monitoring debounce needs custom tuning.

FAQs

Can I bypass F30011 to keep running? No. The G120 firmware does not allow disabling phase-loss detection in any documented way, and bypassing it would mean running a drive on two phases. The diode bridge would survive maybe a few hours at low load before failing — and IGBT modules will follow. Don’t try.

Why does F30011 sometimes show up at night when no one is around? Two common reasons: ambient temperature drops cause connection contraction, opening a marginal joint; or off-peak utility maintenance creates brief phase events on the distribution feeder. Either way the F30011 is real — the drive isn’t imagining it.

My drive is single-phase rated and is single-phase wired. Why does it think I have phase loss? Configuration mismatch. p0205 (or equivalent on your Control Unit firmware) must be set for single-phase operation. Otherwise the firmware looks for three-phase ripple signature, doesn’t find it, and reports F30011. Reference your Power Module’s manual for single-phase configuration — many G120 frames are not single-phase rated at all and you cannot configure them to operate single-phase.

What’s the difference between F30011 and F07802? F30011 is detected by ripple analysis on the DC bus and is the Power Module-side phase loss fault. F07802 (Power supply phase missing) is the Control Unit-side equivalent that also considers the regenerative case for Active Line Module drives. On a standard G120 you’ll see F30011; on an S120 with ALM you might see F07802.

Will a line reactor prevent F30011? No. A line reactor adds impedance and helps with current quality and transient protection, but it can’t synthesize a missing phase. If a phase is gone, it’s gone — the drive will fault regardless of reactor. Reactors do help with the upstream causes (limiting fault currents that blow fuses), so they have indirect value.

Related guides

• Siemens SINAMICS F30001 Fault — Power Module Overcurrent Fix
• Siemens SINAMICS F30003 Fault — DC Link Undervoltage Fix
• Siemens SINAMICS F30021 Fault — Ground Fault Fix

See Also

• Siemens SINAMICS G120 F00001 Fault — Causes & Fix
• Siemens Sinumerik Alarm 300204 — Causes & Fix
• Siemens SINAMICS G120 F30001 Fault — Power Module Overcurrent Fix
• Siemens SENTRON 3WL/3VA Fault Codes — Troubleshooting Guide