Three-phase Quattro: NS undervoltage logged only on L1 | Local event or master reporting?

Q&A and troubleshooting
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Hi everyone,

I’m investigating repeated grid rejection on a three-phase system with three original Quattros, one per phase.

The NS protection log shows “under voltage” only on L1. Does that identify the unit or phase detecting undervoltage, or can L1 log protection events from elsewhere in the system because it is the master?

OBSERVATIONS

We recorded 30 minutes of read-only GX MQTT diagnostics. The system was already disconnected from the grid when the capture started.

AC voltage recorded at the grid meter:
• L1: 237.7–242.8 V
• L2: 240.8–245.4 V
• L3: 239.1–243.9 V

VE.Bus active-input voltage:
• L1: 236.75–242.62 V
• L2: 239.79–244.82 V
• L3: 240.96–245.17 V

Connection and alarm states:
• ActiveInput = 240 and Connected = 0 throughout.
• GridLost = 2 throughout.
• General VebusError = 0 throughout.

Per-device diagnostics:
• MQTT device index 0: SwitchoverInfo/ErrorFlags was normally 8, briefly clearing to 0 and returning to 8 five times.
• MQTT device indices 1 and 2: ErrorFlags remained 0.
• Device 0’s countdown reset 14 times, approximately 127 seconds apart.
• All three devices reported RelayTestOk = 1 and WaitingForRelayTest = 0, with no observed changes.
• Existing interface-protection entries were present under device index 0. No new entry appeared during the capture.

Relevant MQTT paths:

/Devices//ExtendStatus/SwitchoverInfo/ErrorFlags
/Devices//ExtendStatus/SwitchoverInfo/Delay

The countdown payload includes “max”:255, but its measured values were 0–127. We are not treating that metadata as a measured 255-second cycle.

CAPTURE LIMITATIONS

These are remotely published samples, not waveform measurements. The voltage ranges cannot exclude a short dip.

We did not capture the original grid-loss event. We therefore cannot establish whether undervoltage initiated the rejection or appeared during the switching sequence.

DEVICE IDENTITY COMPLICATION

There is also a duplicate displayed serial:

• L1’s displayed serial is genuinely its own.
• L2 displays the same serial as L1, rather than its own.
• L3’s serial is correct.

MQTT device indices 0 and 1 likewise publish the same serial. I am keeping MQTT device index separate from physical phase assignment, rather than assuming index 0 automatically means L1.

QUESTIONS

  1. Is the NS protection log strictly local to each Quattro, or can the L1 master record protection events originating on L2 or L3?

  2. Does ExtendStatus/SwitchoverInfo/ErrorFlags = 8 specifically mean low AC voltage? Is there an authoritative bitfield definition, including any firmware dependencies?

  3. Can NS undervoltage be recorded during relay testing or an unsuccessful connection attempt, rather than being the original reason the grid was rejected?

  4. Is L2 displaying L1’s serial a known configuration or reporting issue, and could it affect diagnostic attribution?

  5. What additional read-only diagnostics would best distinguish a local L1 voltage/sensing event from master-level reporting?

RELATED DISCUSSION

This discussion examines the exact MQTT flag and suggests 8 means VoltageLow, but the contributors explicitly describe the mapping as unverified:

I am not equating this bitfield value with VE.Bus Error 8. The current evidence does not establish a failed relay or inverter.

No electrical settings were changed during the capture.

Any documentation or explanation of the per-unit versus master logging behaviour would be particularly helpful.

Thanks.