PTC Motor Temperature Fault

What does PTC mean?

This fault is triggered when the PTC (Positive Temperature Coefficient) thermistor embedded in the motor windings detects an over-temperature condition. PTC thermistors provide rapid thermal protection due to their steep resistance change above a nominal temperature. This indicates the motor's temperature has reached a critical threshold. Ignoring this fault can lead to rapid motor insulation degradation and ultimate motor failure.

• Motor over-temperature condition, causing the PTC thermistor resistance to rapidly increase and exceed the VSD's trip threshold.
• Open circuit in the PTC sensor wiring (e.g., broken wire, loose terminal connection at motor or VSD).
• Failure or degradation of the PTC thermistor element itself.
• Incorrect PTC input configuration in the VSD (e.g., wrong digital or analog input selected, disabled sensor).
• Electrical noise or interference on the PTC signal lines causing erratic resistance readings.

Click steps to track your progress.

1. 1

   Verify PTC sensor wiring connections at the motor terminal box and VSD input terminals (e.g., dedicated PTC input, or digital input).

2. 2

   Measure the resistance of the PTC sensor at room temperature (e.g., 20-25°C), typically 20-250 Ohms. Measure again when the motor is hot, resistance should be significantly higher.

3. 3

   Confirm the motor's actual temperature using a thermal camera or contact thermometer. Compare to the motor's specified thermal limit.

4. 4

   Disconnect the PTC sensor wires from the VSD. Simulate a healthy PTC by connecting a fixed resistor (e.g., 200 Ohms) to the VSD input terminals and check for fault clearance.

5. 5

   Check VSD parameters (e.g., P1-53 for sensor type = PTC, and P1-56 for PTC trip resistance threshold) are correctly configured.