PTC Thermistor Operation

What does PTC thermistor operation mean?

The resistance of the PTC thermistor connected between terminal 2 and terminal 10 has reached or exceeded the Pr. 561 PTC thermistor protection level setting. This indicates an overheating condition, likely in the motor or associated equipment, which could lead to component damage if the load is not reduced.

• Motor overheating due to sustained overload, insufficient cooling, or high ambient temperature.
• PTC thermistor cable insulation damage or moisture ingress, causing a short or change in resistance.
• Incorrect Pr. 561 (PTC thermistor protection level) setting, making the trip threshold too sensitive.
• Loose connection or corrosion at terminals 2 or 10, causing increased resistance in the measurement circuit.
• Defective PTC thermistor sensor itself, providing an inaccurate resistance reading.

Click steps to track your progress.

1. 1

   Measure motor winding temperature using an infrared thermometer or embedded RTD (Resistance Temperature Detector) if available.

2. 2

   Verify the physical PTC thermistor sensor is properly installed in the motor windings and its cable is undamaged.

3. 3

   Measure the resistance of the PTC thermistor directly at terminals 2 and 10 with the inverter powered OFF (expect ~250-1600 ohms when cold).

4. 4

   Check and adjust Pr. 561 (PTC thermistor protection level) if necessary, ensuring it's appropriate for the thermistor's characteristics.

5. 5

   Inspect terminals 2 and 10 on the inverter control board for secure connections and absence of corrosion.