| Motor Over-speed | Refer to the value of motor speed over P6.1.21 and duration of P6.1.22 |
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ERR29 – Motor Over-Speed
What this means
ERR29 indicates that the VFD detected the spindle motor running faster than the maximum allowed speed for longer than the permitted duration.
In short:
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The spindle exceeded its configured speed limit
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The VFD shut it down to prevent mechanical or electrical damage
This is a protective safety fault, not a random error.
Why the VFD Triggers This Fault
The VFD continuously monitors actual motor speed and compares it to:
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The configured maximum motor speed
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The encoder feedback, if present
If the spindle speed exceeds the allowed threshold defined by:
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P6.1.21 (maximum allowed speed)
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P6.1.22 (time allowed above that speed)
The VFD triggers ERR29.
Most Common Causes We See
1. Encoder configuration mismatch (most common)
If an encoder is used and its settings do not match the motor:
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The VFD may miscalculate actual RPM
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Normal speeds may appear as “over-speed”
Common issues:
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Incorrect encoder type selected
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Incorrect pulses-per-revolution setting
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Loose or intermittent encoder wiring
2. Motor parameter identification not performed
If motor identification has not been run:
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The VFD may not correctly understand the motor’s speed characteristics
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Speed regulation can overshoot during acceleration or load changes
This can cause momentary over-speed conditions.
3. Speed limits set too low
If P6.1.21 is set lower than the actual operating speed:
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Normal spindle operation may exceed the limit
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ERR29 will trigger even though the spindle is behaving normally
4. Rapid acceleration causing overshoot
If acceleration is too aggressive:
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The spindle may briefly overshoot its target RPM
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The VFD detects this as an over-speed condition
This is more likely if acceleration settings are very short.
5. External control mismatch
If the CNC controller commands RPM values that:
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Exceed the VFD’s configured maximum speed
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Do not match the VFD’s scaling expectations
The VFD may see this as a runaway speed condition.
What to Check First
Step 1: Verify commanded RPM
Confirm that:
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The CNC controller is not commanding RPM above the spindle’s rated maximum
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RPM scaling between the controller and VFD is correct
Step 2: Check encoder settings (if applicable)
If your system uses an encoder:
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Confirm encoder type matches the hardware
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Verify pulses-per-revolution setting
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Inspect wiring for looseness or damage
If no encoder is installed, ensure encoder-related functions are disabled.
Step 3: Run motor parameter identification
If available on your VFD:
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Perform motor identification with no load attached
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Ensure motor nameplate values are entered correctly
This allows the VFD to properly model speed response.
Step 4: Review speed limit parameters
Check:
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P6.1.21 – Maximum allowed motor speed
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P6.1.22 – Time allowed above that speed
These should be set:
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Above normal operating RPM
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Below the spindle’s mechanical limits
Overly conservative values can cause nuisance faults.
Step 5: Review acceleration settings
If ERR29 occurs during startup:
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Slightly increase acceleration time
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Prevent RPM overshoot during spin-up
What ERR29 Is Not
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Not a power supply issue
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Not a load or cutting force issue
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Not an EMI or grounding problem
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Not a sign of spindle failure
ERR29 is strictly a speed monitoring fault.
When to Contact Support
If:
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ERR29 occurs at modest RPM
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The spindle never approaches its rated speed
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Encoder settings appear correct but fault persists
Provide:
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Spindle model
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Rated RPM
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Commanded RPM
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Whether an encoder is installed
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Acceleration settings
Summary
ERR29 means the VFD detected the spindle running faster than its configured limit.
Most common causes:
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Encoder configuration errors
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Missing motor identification
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Speed limits set too low
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Acceleration overshoot
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RPM scaling mismatch with the controller
Correct configuration and reasonable speed limits resolve the vast majority of cases.
