Underload Condition

What does UC mean?

This fault occurs when the motor loading level drops below the configured [Underload level] (F611) for a period longer than the [Underload detection time] (F612), and parameter F610 is set to 1 (Fault). It indicates that the motor or driven equipment is not adequately loaded, potentially due to a mechanical issue, disconnection, or incorrect parameter settings. If left unresolved, prolonged underload can cause instability, motor overheating due to inefficient operation, or damage to the motor and driven equipment.

• Loss of mechanical coupling between motor and load (e.g., broken belt, sheared shaft key, coupling failure).
• Reduced material flow or absence of product in process applications (e.g., pump running dry, fan without air resistance, empty conveyor).
• Misconfigured Underload level parameter (F611) set too high for normal minimum load conditions.
• Motor or drive current sensor malfunction providing an erroneously low current reading to the drive controller.
• Accumulation of debris or wear reducing friction/resistance in the driven system (e.g., worn pump impeller, worn brake pad).

Click steps to track your progress.

1. 1

   Visually inspect the mechanical coupling (e.g., belts, shafts, couplings) between the motor and the driven load for damage or disengagement.

2. 2

   Verify the process conditions such as material supply, fluid levels, or air flow are within normal operating ranges for the application.

3. 3

   Measure the actual motor current (terminal U, V, W) during a known underload condition and compare it to the drive's reported output current and parameter F611.

4. 4

   Adjust the Underload detection level (F611) to be 5-10% below the known minimum normal operating current, and/or increase Underload detection time (F612) by 0.5-1.0 seconds.

5. 5

   Check for issues in the motor's power circuit, such as a single-phase loss, by measuring voltage imbalance across the drive's U-V, V-W, W-U output terminals.