When a Danfoss VLT drive trips, it shows an alarm number such as Alarm 7 or Alarm 13 and stops the motor. This guide covers the Danfoss VLT fault codes a maintenance team meets most often, what each one means, the usual cause, and how to clear it. The numbers below are the modern FC-series scheme used by VLT AutomationDrive FC 301 and FC 302, VLT HVAC Drive FC 102, VLT AQUA Drive FC 202 and VLT Midi Drive FC 360. Older VLT 2800, 3000, 5000 and 6000 drives use a different numbering, so always confirm against the manual for your exact model.
Key takeaways
The VLT watches its measured values continuously: DC link voltage, output current, heatsink temperature, and the motor thermal model. When a value leaves its safe window the drive raises a warning first where it can, and trips on an alarm when the condition crosses the trip limit. The display shows the number, the drive coasts the motor to a stop, and the alarm latches. Read the number as a pointer, not a verdict. Alarm 7 DC overvoltage does not mean the drive is broken; it means the DC link climbed too high, usually because a high-inertia load decelerated faster than the drive could dissipate the returned energy.
The warnings and alarms most common on the shop floor, with the number, the name, and the usual cause. The full list for your model is in its programming guide.
| No. | Warning / Alarm | Usual cause |
|---|---|---|
| 2 | Live zero error | A 4-20 mA reference signal was lost |
| 4 | Mains phase loss | A missing or badly unbalanced incoming supply phase |
| 7 | DC overvoltage | DC link too high: fast decel of a high-inertia load, or a line surge |
| 8 | DC undervoltage | DC link too low: supply dip, interruption, or a weak feed |
| 9 | Inverter overloaded | The drive ran above its current rating for too long |
| 10 | Motor ETR over temperature | The motor thermal model reached its limit (overload) |
| 11 | Motor thermistor over temperature | A wired motor thermistor or PTC tripped |
| 12 | Torque limit | Output torque hit the configured limit |
| 13 | Overcurrent | The peak current limit was exceeded (jam, short ramp, fault) |
| 14 | Earth fault | Current leaking from an output phase to ground |
| 16 | Short circuit | A short across the motor output or in the drive |
| 17 | Control word timeout | Fieldbus control word stopped updating |
| 29 | Heatsink over temperature | The power module ran too hot: cooling or ambient |
| 30 / 31 / 32 | Motor phase U / V / W missing | An open output phase to the motor |
| 38 | Internal fault | An internal drive fault, with a subcode for the subsystem |
Alarm 7 DC overvoltage. The DC link went over its limit. On a real line this is almost always a deceleration problem: a loaded conveyor or a high-inertia fan is stopped faster than the drive can bleed off the energy the motor returns. Extend the ramp-down time, enable the overvoltage control, or fit a brake resistor sized for the load. This is the same physics as a VFD overvoltage fault on any brand.
Alarm 8 DC undervoltage. The DC link dropped too low. Look upstream: a sagging supply, a loose incoming terminal, or a shared feed with a large motor or welder that pulls the line down on start. Confirm the input voltage under load.
Alarm 9 inverter overloaded and Alarm 10 motor over temperature. Alarm 9 is the drive protecting itself; Alarm 10 is the motor thermal model. Both usually mean the load grew or the duty is heavier than the sizing. Check the mechanical load, then confirm the motor data in the parameters matches the nameplate.
Alarm 13 overcurrent. Output current spiked past the peak limit. Check the mechanics first (a jam or seized bearing), then the acceleration ramp, then the motor cable. This is closely related to a VFD overcurrent fault.
Alarm 14 earth fault and Alarm 16 short circuit. Both are genuine electrical faults, not nuisance trips. Megger the motor and the motor cable, inspect the glands and terminations for damage or moisture, and repair before running again. A recurring earth fault on the same motor points to failing winding insulation and planned replacement, not repeated resets. See ground fault protection.
Alarm 29 heatsink over temperature. The power module overheated. Clean the heatsink, check the cooling fan and enclosure ventilation, and confirm the ambient temperature. A drive in a sealed panel next to a heat source will trip on a hot day even when nothing electrical is wrong.
Do not reset an alarm until you know why it tripped. Once the cause is fixed, most VLT alarms reset from the keypad Reset button, from a configured digital-input reset, over the fieldbus, or by cycling power. A few trip-lock alarms, such as Alarm 16 short circuit or Alarm 38 internal fault, need a full power cycle and the DC bus fully discharged before they will clear. If the alarm returns the instant you run, the condition is still present, and clearing an earth fault or a short circuit just to keep the line moving risks a burned motor or a damaged drive.
One overvoltage trip is an event. The same VLT tripping on Alarm 7 every time it stops, or on Alarm 29 every summer afternoon, is a pattern that predicts a failure. Teams that stay ahead of drive faults do not just reset them, they log them: which alarm, which asset, which shift, how often. That record is where a stopped machine becomes a scheduled fix instead of a surprise.
This is what a CMMS and predictive maintenance software are for: capturing every trip against the asset, surfacing the drives that fault most, and raising a work order before the next one stops the line. If drive faults are turning into unplanned downtime, book a demo and we will show you how the recurring ones get caught early.
Related reading: VFD overvoltage fault, VFD overcurrent fault troubleshooting, and fault-code guides for other drives: ABB, Siemens Sinamics, Schneider Altivar and Yaskawa.
What is the difference between a warning and an alarm on a Danfoss VLT? A warning flags a problem while the drive keeps running; an alarm trips the drive and latches until reset. Many conditions show as a warning first and become an alarm if they persist or worsen.
What is the most common Danfoss VLT alarm? On most lines it is Alarm 7 DC overvoltage or Alarm 8 DC undervoltage, both supply and deceleration issues, followed by Alarm 9 inverter overloaded and Alarm 13 overcurrent.
How do I reset a Danfoss VLT alarm? Fix the cause first, then press Reset on the keypad, use a configured reset input, reset over the fieldbus, or cycle power. Trip-lock alarms such as Alarm 16 need a full power cycle.
Do these numbers apply to my older VLT drive? These are the FC-series numbers (FC 301, FC 302, FC 102, FC 202, FC 360). VLT 2800, 3000, 5000 and 6000 use a different scheme, so check the manual for your model.
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