VSD communication / fieldbus fault
The drive has lost communication with the PLC/SCADA over its fieldbus (e.g. control by network) — comms-loss fault, no remote control, or the drive stops on comms timeout.
Safety first
A comms-loss can stop or (if configured) hold the drive in a state. Confirm the configured comms-loss behaviour so you're not surprised by motion. Isolate before handling wiring.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Network cabling / connector fault
Most likelyA broken, loose, or poorly terminated network cable interrupts comms.
- 2
Address / configuration mismatch
#2Wrong node address, baud rate, or protocol settings stop the drive talking to the master.
- 3
Termination / wiring fault on the bus
#3Missing or incorrect bus termination causes unreliable comms across the segment.
- 4
Master (PLC) not communicating
#4The PLC/SCADA side is faulted, in stop, or mis-configured.
- 5
Comms card / port fault
Least likelyThe drive's comms option card or port has failed.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeCheck the drive's comms status LEDs and read the exact comms fault/code.
Comms indicators show a healthy, active link.
Link looks up — check addressing/config and the master.
Link down — check cabling, termination, and the port.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
VSD comms fault
→ step 2 - 2decision
Do the comms LEDs show a healthy link?
Yes→ step 3No→ step 4 - 3decision
Do address/baud/protocol match and is the master active?
Yes→ step 5No→ step 6 - 4decision
Are cabling and bus termination sound?
Yes→ step 3No→ step 7 - 5result
Suspect the comms card/port — replace per procedure.
- 6result
Mismatch or master down — correct settings / fix master.
- 7result
Cabling/termination fault — repair it.
Common mistakes apprentices make
- Not checking the configured comms-loss behaviour before testing.
- Overlooking missing/incorrect bus termination.
- Address or baud-rate mismatch after a replacement.
- Assuming the drive when the PLC master is in stop.
When to stop & escalate
Network architecture and master-side faults may involve the controls/automation team. Comms-card replacement should follow the drive's procedure and any saved configuration.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
PLC output LED is on but the device doesn't work
The PLC output indicator says the output is energised, but the connected device (valve, contactor, lamp, motor starter) does nothing. The program thinks everything is fine.
VSD powered up but won't start the motor
The drive is energised and the display is alive, but it won't run the motor. No fault may be shown — it just sits in 'ready' or 'stopped' and ignores the start command.
PLC communication fault (network / remote I/O)
The PLC has lost communication with a device, remote I/O, HMI, or network — comms-fault indication, missing data, or remote I/O dropping out.