ATV12 – What would cause the drive to show ULF (Underload Fault)?

The ULF (Underload Fault) occurs when the drive detects that the motor current is below a configured threshold for a defined period of time.

According to the ATV12 manual:

• The parameter [ULt] (Application underload time delay) enables and controls this function
• Location:
  [ConF] → [FULL] → [I_O-] → [ULt]

• If ULt > 0, underload monitoring is active
• If the motor current drops below the threshold (LUL) for longer than ULt, the drive trips with ULF fault

• ULt (Underload time delay)
  • Range: 0–100 s
  • 0 = disabled (default)
• LUL (Underload threshold)
  • Typically set as % of nominal current (default ~60%)

✅ Typical Cause

• Underload monitoring was enabled (ULt > 0)
• The motor current fell below the configured threshold (LUL) long enough to trigger the fault

This can happen due to:

• Loss of load (broken belt, uncoupled shaft)
• Pump running dry / cavitation
• Light or no process load

✅ How to Resolve

• If underload protection is not required:
  👉 Set ULt = 0 s (disables the function)

• If protection is required:
  👉 Adjust:

  • ULt (delay)
  • LUL (threshold)
    to match the normal operating load of the application

If this article does not answer your question, check out our FAQ database that has answers to more commonly asked questions:

Frequently Asked Questions - Schneider Electric (se.com)

If this FAQ did not solve your issue, you can call us at 1-888-778-2733 Option 2 and then 4 or e-mail us atdrive.products.support@se.comto create a case with our Technical Support Team.

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