IndustrialDriveDataDrive Board & Diagnostic Database
Control Techniques / Nidec fault record

O.ht / O.ht1: Heatsink or Thermal Overload Trip

Unidrive reports O.ht or O.ht1 after load operation, high ambient temperature or poor cabinet cooling.

Meaning of the indication

The drive thermal path has exceeded its safe boundary or the temperature feedback is not credible. Route by cold-start versus hot-load timing.

Checking order

  1. Classify whether the trip appears cold or only after load.
  2. Inspect fan, heatsink dust, filter and cabinet airflow.
  3. Compare output current and switching duty with drive rating and derating conditions.
  4. Record ambient temperature and enclosure condition.
  5. If a cold trip appears, investigate temperature feedback or electronics after safe isolation.

Suspect areas

Cooling fanBlocked heatsinkCabinet ventilationOverloadTemperature sensorControl board
Fault-specific caution

Thermal trips are protective; bypassing cooling evidence accelerates power-stage and capacitor failure.

Diagnostic workflow

Workflow
Unidrive PS.24V / Thermal / Feedback Evidence Workflow

Unidrive reports PS.24V, thermal feedback symptoms, O.ht/O.ht1 or feedback instability with option modules and external control wiring.

Open →