Motor Overheat Fault (Level 4)

What does OH4 mean?

The OH4 fault indicates a critical over-temperature condition in the motor, detected when the motor temperature analog input (H3-09=E) surpasses the 2.34V fault level. Upon activation, the drive will immediately stop the motor using a configured method to prevent damage. Operating a motor under this severe overheat condition risks immediate insulation breakdown, permanent motor failure, and safety issues.

• Severe and prolonged mechanical overload on the motor, leading to excessive current draw and heat generation, exceeding thermal capacity.
• Motor winding insulation breakdown due to excessive temperature cycling, aging, or voltage spikes, resulting in inter-turn shorts.
• Drive operation beyond the motor's continuous duty rating, for example, sustained low-speed operation without adequate forced ventilation (Parameter H3-09=E implies feedback).
• Malfunctioning motor temperature sensor (e.g., shorted, incorrect type) providing erroneous high-temperature feedback to analog input H3-09.
• Drive current limit (Parameter L1-02) set too high or disabled, allowing the motor to draw excessive current without tripping on a primary overload fault (OL1).

Click steps to track your progress.

1. 1

   Disconnect power and perform a full mechanical inspection of the driven load for binding, seize-ups, or excessive friction. Free any obstructions.

2. 2

   Using an insulation tester (e.g., Megger MIT420), perform motor winding insulation resistance tests phase-to-phase and phase-to-ground (500VDC for 1 minute).

3. 3

   Measure the resistance of the motor temperature sensor (e.g., PT100 or PTC) directly at the motor terminals and compare to its datasheet values at ambient temperature.

4. 4

   Verify the drive's analog input for the temperature sensor (e.g., H3-09) by applying a calibrated voltage source to simulate different temperature values and check drive response.

5. 5

   Monitor motor current (Amps) on all three phases using a clamp meter (e.g., Fluke 376 FC) during operation and compare against the motor's nameplate FLA.

6. 6

   Check Parameter H3-09 (Motor Temperature Input Type) and ensure it is correctly configured for the sensor installed (e.g., 'E' for PT100/PTC via analog input) and verify wiring.