Scope of this technical record
Danfoss VLT FC-series diagnostic records for alarm 14 earth fault, alarm 16 short circuit, alarm 4 mains phase loss, alarm 29 heatsink temperature and overvoltage during deceleration.
These records are for qualified drive-service personnel. Input, DC-link and output terminals remain hazardous after stop; isolate power and verify discharge before internal inspection.
Why Danfoss VLT alarms need structured routing
VLT alarm searches often arrive with only a number: alarm 14, alarm 16, alarm 4 or alarm 29. The commercial value is not in repeating the alarm title. It is in converting that number into a safe evidence chain that separates external motor/cable or line problems from internal drive electronics.
The FC-series service platform record therefore groups alarms by hardware boundary: input phase and DC link, output earth/short path, cooling/heatsink path and braking/deceleration path.
Alarm-to-boundary map
Alarm 14 and alarm 16 overlap at the motor-output boundary but need different evidence. Alarm 4 begins at the input terminals and protection path. Alarm 29 needs thermal evidence before a board conclusion. Deceleration overvoltage requires load-inertia and brake-path evidence.
Danfoss VLT first-pass routing
| Alarm / symptom | First boundary | Evidence to preserve |
|---|---|---|
| Alarm 14 earth fault | Motor/cable insulation, PE leakage, output stage | Motor connected result, insulation evidence |
| Alarm 16 short circuit | Output cable, terminals, IGBT/driver | Trip timing and previous module repair |
| Alarm 4 mains phase loss | Input phases, fuses, contactor | Phase voltage at drive terminals |
| Alarm 29 heatsink temp | Fan, heatsink, ambient, load, sensor path | Cold versus hot trip timing |
Repair implication
If the alarm remains with external wiring removed under safe conditions, the support path moves toward the drive power stage, current detection, rectifier/DC-link or temperature feedback. If the alarm disappears when the motor/cable is isolated, the replacement drive is not the first purchase; the external installation must be corrected first.
Field record checklist
- Full VLT type code and frame/rating
- Alarm number and exact displayed wording
- Trip timing and load condition
- Input voltage at drive terminals for phase-loss cases
- Motor/cable isolation evidence for alarm 14/16
- Fan/heatsink/ambient evidence for alarm 29
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Database layer for VLT alarm routing.
Model records
Fault records
The Danfoss VLT reports alarm 14, trips on start or trips when the motor cable is connected.
The VLT reports alarm 16 or trips instantly when the inverter output is enabled.
The VLT reports mains phase loss, trips at power-up, or loses ready state when plant load changes.
The VLT trips on alarm 29 during load, in high ambient temperature, or after cooling airflow has degraded.
The VLT trips on overvoltage when the machine slows down, stops a high-inertia load or lowers a regenerative load.
Circuit and diagnostic records
Routes alarm 4 and deceleration overvoltage through line phases, fuses, contactor, rectifier, DC-link ripple, high line voltage and braking energy paths.
Routes alarm 14 and alarm 16 through output insulation, terminal contamination, motor cable damage, IGBT module, gate driver and current-feedback path.
Routes alarm 29 through cooling fans, heatsink contamination, airflow, cabinet ventilation, ambient temperature, load current and temperature feedback.
Danfoss VLT reports alarm 14 earth fault or alarm 16 short circuit.
Danfoss VLT reports alarm 4 or shows input phase instability.
Danfoss VLT reports alarm 29 during operation or immediately after power-up.
Danfoss VLT trips on overvoltage during deceleration, stop or load lowering.