Overview
One breaker on the bus stops returning measurements while every other device on the same controller continues to report normally. The two most common causes are reversed RS485 wires on that specific device, or a wire that was never tightened properly and has worked loose. Both produce nearly identical symptoms and both require an on-site inspection to confirm.
How this issue is diagnosed
This fault is resolved jointly between the installer on site and Hybird support. The installer reports the symptoms and performs the physical inspection and wiring fix; Hybird support reads the controller logs from Hybird Admin to confirm the symptom pattern and rule out other causes. If the symptoms in the next section match what you are seeing, contact Hybird support at [email protected] or +45 3020 4900 to begin the joint diagnosis.
Symptom
One Modbus ID has stopped returning data while every other device on the same controller continues to report normally.
The symptom may appear immediately after commissioning (installation error) or weeks or months later (wire worked loose over time).
From the support side, controller logs in Hybird Admin show repeated Modbus errors against that one address. The log line is in the form:
[ERROR] [GET_MEASUREMENTS] Failed to read measurement from Device <modbus_id> (<device_type>): Modbus error: Modbus query timed out
For example: [2026-05-27T13:49:55Z] [ERROR] [GET_MEASUREMENTS] Failed to read measurement from Device 2 (Breaker): Modbus error: Modbus query timed out. Log format may change over time as the underlying libraries are updated, so search by symptom rather than by exact string.
Possible causes
Reverse polarity on the device. The two RS485 wires (A and B) are swapped at this one breaker. Easy to miss because the wire pair is small, often closely matched in colour, and sits in a crowded panel. Installers frequently report "wires are correct" on first inspection when they are not · one wire typically has a faint stripe and the other is solid, and the difference is easy to overlook.
Loose wire on the device. One of the RS485 conductors was not fully seated or was under-tightened at install, or has worked loose since. Vibration, thermal cycling, or any subsequent work in the panel can shift a marginal connection.
Reverse polarity is the more common of the two. Both produce the same symptoms in the logs, so confirmation is always physical.
Diagnosis
Hybird support will confirm from the controller logs that only one Modbus ID is producing timeout errors and that the rest of the bus is healthy. Support will also check whether the device has ever reported successfully:
A device that has never reported since commissioning points to an install-time wiring error.
A device that reported successfully for some period and then stopped points to a loose wire or post-install panel work.
If the log pattern matches a group of devices going offline together rather than a single one, the issue is likely a daisy chain break instead · see Group of breakers offline · troubleshooting guide.
Once the single-device symptom is confirmed, the installer performs the physical inspection on site:
At the affected breaker, inspect both RS485 conductors. Identify A and B by the wire marking (one conductor carries a stripe; the other is solid). Compare against an adjacent, working breaker to confirm the convention used in this panel.
Gently tug each RS485 wire at the breaker terminal. Any movement indicates the wire was not properly seated.
For a fuller checklist of what to inspect on site, see On-site visual checks · what to inspect on a Hybird panel.
RS485 is low-voltage signal wiring and can be worked on with the panel live. Do not de-energise the panel · the installation is likely powering active loads. Apply standard panel-work precautions: avoid contact with AC terminals, and follow local regulations (Stærkstrømsbekendtgørelsen in Denmark, BS 7671 in the UK, VDE 0100 in Germany) for working inside a live distribution panel.
Resolution
Correct the wiring at the affected breaker on site · either reverse the A/B pair if they are swapped, or re-seat and properly secure any loose conductor. The panel can remain energised.
The RS485 plug is push-in and hand-tightened; no torque value applies. Confirm the wire is fully inserted and will not pull out under light tension.
Hybird support will confirm from Hybird Admin that the affected Modbus ID is reporting again and that the timeout errors have cleared.
Prevention
At commissioning, verify every breaker reports correctly before closing the panel. A single-device wiring fault is only reliably detected by attempting to poll every device · visual inspection alone is unreliable.
Pay particular attention to A/B polarity on the RS485 pair. Confirm the wire marking convention with the rest of the panel before terminating.
After any subsequent panel work, confirm with Hybird support that all devices remain online before leaving site.
When to escalate
If the affected device still does not report after the wiring has been corrected and re-seated, contact Hybird support at [email protected] or +45 3020 4900 for further diagnostics. In rare cases the breaker itself may be faulty, in which case advance replacement under warranty applies · but most single-device faults are resolved by correcting the wiring or by remote register-level support, without replacement.
Summary
A single breaker dropping off the bus while everything else continues to report is almost always a wiring fault on that device · reverse polarity at install, or a wire that has worked loose. The fix is straightforward once confirmed on site, but installer self-reports of "wires are correct" should always be verified physically.