Undertorque Detection 1

What does UL3 mean?

The Drive output current dropped below the threshold set in L6-02 for longer than the time set in L6-03, indicating a motor underload condition. This often signifies a mechanical failure such as a broken belt or coupling, or a sudden loss of load on the motor.

• Mechanical coupling failure between the motor and the driven load (e.g., broken belt, sheared key, decoupled shaft).
• Process interruption causing the load to become lighter than expected (e.g., pump running dry, material feed stopping, unchoked conveyor).
• Incorrectly set undertorque detection threshold (Parameter L6-02) or delay time (Parameter L6-03) leading to false trips during normal operation.
• Motor current sensor calibration drift within the drive causing an inaccurate reading of the actual motor current.
• Motor winding damage or internal short circuit leading to reduced current draw for a given mechanical output.

Click steps to track your progress.

1. 1

   Safely disconnect power to the motor and physically inspect the mechanical connection between the motor shaft and the driven load for damage or disengagement.

2. 2

   Verify the actual motor load by monitoring the output current (e.g., through the drive display or with a current clamp) during operation and compare it to the undertorque threshold set in Parameter L6-02.

3. 3

   Adjust the undertorque detection threshold (Parameter L6-02) and/or the delay time (Parameter L6-03) if the actual operating current consistently falls close to or below the current setting.

4. 4

   Manually rotate the driven load (if safe and possible) to check for unexpected looseness or freedom of movement that indicates a detached load.

5. 5

   Measure the resistance of each motor phase winding (U-V, V-W, W-U) using a multimeter; compare readings for consistency and against motor specifications to detect internal motor damage.