TL;DR
Overvoltage faults during deceleration mean the bus cannot absorb regenerative energy fast enough. Lengthen the decel ramp first. If the load is high-inertia, add a dynamic braking resistor.
What you might see
- F005 or OV fault on drive display
- drive trips during deceleration
- bus voltage reading above drive rated limit
- drive trips under regenerative load
Likely causes
Regenerative braking energy during deceleration exceeding the drive's DC bus absorption capacity
Supply-side voltage transient (utility surge or capacitor switching) pushing the bus above the trip threshold
Decel ramp time set too short for the load inertia
No dynamic braking resistor on a high-inertia load
Required tools
- True-RMS multimeter rated for 600V
- HIM keypad or Connected Components Workbench laptop
- Arc-flash PPE (for energized measurement)
- Dynamic braking resistor (if needed, sized per AB resistor selector guide)
Safety first
- VFDs retain lethal DC bus voltage for several minutes after input power is removed. Wait at least 5 minutes and verify bus voltage below 50V DC before touching any internal component.
- All energized measurements inside the drive enclosure require arc-flash PPE and an Energized Electrical Work Permit.
Procedure
- 1
Check the drive display or fault queue for the exact fault code. F005 is the standard PowerFlex 525 overvoltage fault.[1]
- 2
Review the decel time parameter (A442, Decel Time 1). Increase it by 50% and perform a test stop.[1]
- 3
Monitor the DC bus voltage via the drive HIM display or connected software (BootP/Connected Components Workbench) during a decel event.
- 4
If the bus still spikes above the trip level after lengthening decel time, the load inertia is too high for the drive alone. A dynamic braking resistor is required.
- 5
Verify the supply voltage is within the drive's rated input range (usually 480V AC, -10%/+10%). Check with a true-RMS multimeter.
Warning: Measuring VFD input terminals requires opening an energized enclosure. Use arc-flash PPE and category-rated test leads. - 6
If supply transients are suspected, install a line reactor on the drive input or upgrade to a drive with a built-in line reactor.
- 7
Clear the fault by pressing Stop/Reset on the HIM keypad, then run a controlled test cycle.
Sources
Allen-Bradley PowerFlex 520-Series AC Drives User Manual (Pub 520-UM001), Rockwell Automation (Allen-Bradley)
Allen-Bradley PowerFlex 520-Series User Manual, general overvoltage fault diagnosis and decel ramp parameter procedures (general)
View source
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