VFD Fault Codes Across Brands: What OC, OV, OL and OH Are Actually Telling You
The short answer
Whatever the drive, faults fall into six families: overcurrent, overvoltage, undervoltage, overload, overtemperature and earth fault. The code on the display differs by brand but the physics does not. Overcurrent means the drive saw current rise faster than it could control, overvoltage almost always means the load drove the motor during a deceleration, and overload means the drive was within its current limit but for too long. Resetting a drive without deciding which family it was in is how a drive gets replaced for a mechanical problem.
The families, and what they physically mean
Overcurrent, often OC, F001, 2310, OCA/OCD/OCN. Instantaneous current above the drive's trip level. Physically: a short or an earth fault on the output, a shorted motor winding, an acceleration ramp too fast for the load inertia, or a mechanical jam. If it trips the instant you press start, suspect wiring or the motor. If it trips only during acceleration, suspect the ramp or the inertia.
Overvoltage, OV, F002, 3210. DC bus voltage above limit. Almost always regeneration: the load has more kinetic energy than the deceleration ramp can absorb and drives the motor as a generator. High-inertia loads and overhauling loads such as hoists and downhill conveyors do this. The cures are a longer ramp, a braking resistor, a regenerative front end, or enabling the drive's DC bus voltage controller so it extends the ramp automatically. Persistent overvoltage with no deceleration involved means a supply problem.
Undervoltage, UV, F004, 3220. DC bus below limit. Supply dips, a phase lost on the input, a loose incoming terminal, a badly sized transformer, or a large motor starting nearby on a weak supply. On a plant with frequent brief dips, the drive's ride-through or kinetic buffering settings matter more than the trip level.
Overload, OL, F005, thermal model trips. Current inside the instantaneous limit but sustained above the continuous rating for longer than the drive's thermal model allows. Physically: the machine is harder to turn than it should be, the motor is undersized, the drive is undersized, or the motor is running loaded at low speed with insufficient cooling. Note that a self-cooled motor at 15 Hz has very little airflow and its true continuous rating there is far below nameplate.
Overtemperature, OH, OHT, 4210. Heatsink or internal temperature. Blocked filters, failed cooling fan, ambient above the panel's design, drives mounted too close together, or a drive derated for the switching frequency someone raised to make the motor quieter. See panel thermal design.
Earth fault, GF, F013. Current leaving on the earth path. Damaged motor cable, moisture in a terminal box, a failing winding. Long unscreened motor cables with high switching frequency also produce capacitive leakage that can trip sensitive detection with nothing actually wrong, which is a real effect and not a reason to ignore the fault.
The brand names for the same thing
| Family | Siemens SINAMICS | Allen-Bradley PowerFlex | ABB ACS | Delta | Schneider Altivar |
|---|---|---|---|---|---|
| Overcurrent | F30001, F7801 | F5 OverCurrent | 2310 OVERCURRENT | ocA/ocd/ocn | OCF |
| Overvoltage | F30002 | F4 DC Bus Overvolt | 3210 DC OVERVOLT | OV | OSF/ObF |
| Undervoltage | F30003 | F3 Power Loss | 3220 DC UNDERVOLT | Lv | USF |
| Overload | F30005 | F7 Motor Overload | 5090 / thermal | oL / oL1 | OLF |
| Overtemperature | F30004 | F8 Heatsink OvrTmp | 4210 | oH1 | OHF |
| Earth fault | F30021 | F13 Ground Fault | 2330 EARTH FAULT | GFF | see manual |
Always confirm against the manual for the exact firmware: codes move between families across generations.
Finding the cause instead of resetting
- Read the fault log with timestamps and the trip data, not just the active fault. Most drives store output current, frequency and DC bus voltage at the moment of trip, which tells you the family immediately.
- Ask when it trips: at start, during acceleration, during deceleration, at steady speed under load, or randomly. Each points at a different family.
- Check the mechanical side before the electrical. A drive tripping on overcurrent or overload is very often reporting a real mechanical problem accurately.
- Megger the motor and cable if overcurrent or earth fault is involved, with the drive disconnected.
- Only then change parameters, and record what you changed.
Raising the current limit or extending the thermal model to stop a nuisance trip is occasionally right and usually removes the protection that was telling you something true.
Where to learn it
VFD and variable frequency drives covers the theory, parameters and commissioning; Siemens SINAMICS with Startdrive and Allen-Bradley PowerFlex cover the two most common platforms in Indian plants. Related reading: VFD parameter setup the first time and DOL vs star-delta vs soft starter vs VFD.
Frequently asked questions
The drive trips only in summer. Overtemperature, and the panel is the cause rather than the drive. Check filter condition, fan operation and the panel's thermal calculation at real ambient.
Can I just increase the acceleration time to stop overcurrent trips? Often yes, and it is the correct fix when the load inertia is genuinely large. It is the wrong fix when the real cause is a jammed machine or a failing bearing.
Why does a braking resistor fix overvoltage? It gives the regenerated energy somewhere to go as heat, so the DC bus does not rise. Size it for the duty cycle, not just the peak, or the resistor becomes the next fault.
