AdvancedMedium risk

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.

Start fault-finding

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.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

1
Network cabling / connector fault
Most likely
A broken, loose, or poorly terminated network cable interrupts comms.
2
Address / configuration mismatch
#2
Wrong node address, baud rate, or protocol settings stop the drive talking to the master.
3
Termination / wiring fault on the bus
#3
Missing or incorrect bus termination causes unreliable comms across the segment.
4
Master (PLC) not communicating
#4
The PLC/SCADA side is faulted, in stop, or mis-configured.
5
Comms card / port fault
Least likely
The drive's comms option card or port has failed.

Reports are saved on this device to reflect what you actually find.

Premium fault tree

The full ranked causes, test sequence and flowchart for this fault are part of Sparkie Sidekick Pro.

Coming soon — no payment required during preview.

Testing sequence

Work through one test at a time. Expected reading and what each result means.

Test 1 of 3

Check the drive's comms status LEDs and read the exact comms fault/code.

Expected reading

Comms indicators show a healthy, active link.

Your actual reading

If it passes

Link looks up — check addressing/config and the master.

If it fails

Link down — check cabling, termination, and the port.

Often leads toPLC output LED is on but the device doesn't work VSD powered up but won't start the motor

View all expected readings at once

1. Check the drive's comms status LEDs and read the exact comms fault/code.

Comms indicators show a healthy, active link.

2. Verify the network cabling, connectors, and bus termination on the segment.

Sound cabling and correct termination.

3. Confirm node address, baud rate, and protocol match the master; check the master is communicating.

Matching settings and an active master.

Full test sequence

The step-by-step test flow with expected readings for this fault is part of Sparkie Sidekick Pro.

Coming soon — no payment required during preview.

Fault-finding flowchart

The same logic as a decision tree.

1
start
VSD comms fault
→ step 2
2
decision
Do the comms LEDs show a healthy link?
Yes→ step 3No→ step 4
3
decision
Do address/baud/protocol match and is the master active?
Yes→ step 5No→ step 6
4
decision
Are cabling and bus termination sound?
Yes→ step 3No→ step 7
5
result
Suspect the comms card/port — replace per procedure.
6
result
Mismatch or master down — correct settings / fix master.
7
result
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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