A VFD overvoltage fault, shown as OV, Ou, or F005 depending on the brand, means the drive's internal DC bus voltage climbed above its safe limit and the drive tripped to protect itself. On a real production line the cause is almost never the drive. It is the load pushing energy back faster than the drive can get rid of it. This guide explains why VFD overvoltage faults happen and how to stop them.
Key takeaways
Inside every variable frequency drive is a DC bus: a bank of capacitors holding the rectified supply voltage that the drive chops back into a variable-frequency output for the motor. The drive watches that bus voltage constantly. When it rises above the trip threshold (on a 400 V drive, typically around 800 V DC), the drive faults and coasts the motor to a stop rather than let the overvoltage damage the capacitors or the output transistors.
The fault name depends on the brand: F005 on an Allen-Bradley PowerFlex 525, OV or Ou on many others, an overvoltage code on Yaskawa and Mitsubishi drives. The code differs; the physics do not.
1. Deceleration of a high-inertia load, by far the most common. When a spinning load decelerates faster than it would naturally coast, the motor becomes a generator and pushes energy back into the drive. That energy has nowhere to go but the DC bus, and the bus voltage climbs. A loaded conveyor, a large fan, a centrifuge, or a flywheel told to stop in a couple of seconds will trip on overvoltage every time.
2. A high or surging incoming supply. If the incoming line voltage is already high, or the plant has switching transients and surges, the rectified bus sits close to the trip point and small events push it over. Measure the actual supply voltage. That is live work inside the panel, so it needs a qualified person with a properly rated meter and the arc flash PPE your site requires, or read the drive's own DC bus monitor instead (see below). A nominal 400 V line running at 440 V lifts the resting bus from about 565 V to about 620 V, which leaves less headroom for the energy a decelerating load sends back. High line on its own rarely trips a drive; it turns a borderline stop into a trip.
3. A missing or failed braking resistor. Drives meant to stop hard use a braking resistor to burn off the returned energy as heat, switched in by a braking transistor or chopper. If the resistor is disconnected, open, or undersized, the energy has nowhere to go and the bus rises.
4. Regeneration from an overhauling load. Some loads drive the motor even when it should be holding back: a downhill conveyor, a hoist lowering a weight, an unwinder under tension. The motor generates continuously, and without a way to return or dissipate that energy the drive faults.
Extend the deceleration time. The simplest fix. Give the load longer to slow down so the returned energy trickles in instead of flooding the bus. If a longer decel is acceptable for the process, this alone clears most overvoltage trips.
Safety first: a braking resistor is wired to the DC bus, which stays charged after the supply is switched off, and a working resistor can be hot enough to burn. Lock out the drive supply, wait at least the discharge time on the drive warning label (three minutes on a PowerFlex 525, five minutes on Yaskawa drives), then measure between DC+ and DC- and confirm zero volts before you touch the resistor or its wiring. A dark display does not mean the bus is discharged.
Fit or check a dynamic braking resistor. When the process needs a fast stop, a correctly sized braking resistor and chopper burn off the energy the load returns. Confirm the resistor is connected, unbroken, and rated for the load. This is the standard answer for high-inertia stops.
Enable the drive's own bus regulation. Many drives can automatically stretch the decel ramp when the bus starts to climb. It trades a longer stop for no trip. Use it as an alternative to a braking resistor, not together with one, and do not expect it to cure continuous regeneration. A PowerFlex 525 raises a Stall Fault if the regulator holds the ramp for a full minute.
Fix the supply. If the line is high, correct the transformer tap or supply voltage. If transients are the problem, a line reactor smooths them and gives the bus more margin.
For continuous regeneration, size for it. An overhauling load needs either a braking resistor rated for continuous duty or a regenerative, four-quadrant drive that returns energy to the line. A standard drive with a small resistor will keep tripping.
Genuine drive-hardware causes of an overvoltage trip are rare: a failed bus-voltage sensing circuit, or a braking transistor stuck open. Suspect the drive only after you have confirmed the supply voltage is in range and the deceleration and braking are correct. On most lines, replacing a drive for an overvoltage fault replaces the wrong part.
One overvoltage trip during commissioning is expected. The same drive tripping on overvoltage every time it stops is a sizing decision that was never made: the decel is too aggressive for the inertia, or the braking is missing. Teams that eliminate these faults do not just reset them, they record which drive trips, on which duty cycle, how often, and feed that into the fix.
That record is what a CMMS with PLC connectivity captures: every trip against the asset, so a recurring overvoltage becomes a work order to add a braking resistor rather than a nightly reset. If drive faults are stealing uptime, book a demo and we will show you how the repeat offenders surface early.
Related reading: PowerFlex 525 fault codes, where F005 is overvoltage, and Yaskawa VFD fault codes.
Every drive shows its DC bus voltage live, for example parameter b005 [DC Bus Voltage] on a PowerFlex 525. At rest the bus sits near 1.4 times the line voltage, so about 565 V on a 400 V supply. Watch it through a normal stop. If it climbs toward the trip level only while the motor decelerates (810 V DC on a 380 to 480 V PowerFlex 525), the load is regenerating and the fix is decel time or braking. If it already sits high with the motor stopped, look at the supply, not the load.
On a PowerFlex 525, P042 [Decel Time 1] sets the stop ramp and defaults to 10 seconds, A437 [DB Resistor Sel] enables an external braking resistor and sets its protection level, and A550 [Bus Reg Enable] turns the bus regulator on or off. It ships enabled. On Yaskawa drives, L3-04 (Stall Prevention during Deceleration) plays the same role and is also on by default, and the Yaskawa braking option manual says to set it to 0 when a braking resistor or other braking option is fitted. Change one setting at a time and log the result against the drive.
With the drive locked out and the bus verified at zero volts, check the resistor itself: measure its resistance and compare it with its label and with the minimum resistance given in the drive manual, and look for heat damage and loose terminals. Then check that the drive knows the resistor is there. On a PowerFlex 525, a resistor wired to a drive with A437 [DB Resistor Sel] still at 0 (Disabled) is never switched in, so the drive trips on overvoltage exactly as if the resistor were missing.
What causes a VFD overvoltage fault? Almost always decelerating a high-inertia load too fast, so the motor returns energy to the DC bus. A high supply voltage, a missing braking resistor, or an overhauling load are the other causes.
How do I stop a VFD tripping on overvoltage? Extend the decel time, fit or repair a correctly sized dynamic braking resistor or, if no resistor is fitted, enable bus-voltage regulation, and confirm the incoming supply is not running high.
What is the overvoltage trip level on a 400 V drive? Typically around 800 V on the DC bus, though the exact figure is in the drive manual. The bus is roughly 1.4 times the AC supply, so a high line eats into the headroom the drive has for regenerated energy.
Does an overvoltage fault mean the drive is faulty? Rarely. It usually means the system is returning more energy than the drive can dissipate. Check the supply, the decel time, and the braking before you suspect the drive.
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