Motor Underload (Undercurrent)

What does UCF mean?

The motor is drawing significantly less current than expected for its configured operating conditions. This typically indicates a loss of mechanical load, a broken belt/coupling, or an issue with the motor itself running unloaded.

• Mechanical load disconnected or significantly reduced (e.g., broken belt, sheared coupling key, valve closed, pump running dry).
• Incorrect motor full load current (FLA) or overload class (OCL) parameters configured in the soft starter (e.g., rAt parameter).
• Motor running with significantly less mechanical load than anticipated for its rated power.
• Failure of a process sensor (e.g., pressure sensor, flow sensor) causing the motor to operate without proper load.
• Faulty current sensing circuit within the soft starter leading to inaccurate current readings (less common).

Click steps to track your progress.

1. 1

   1. Visually inspect the mechanical connection between the motor and the driven load (e.g., check belts for breaks, couplings for damage, shafts for shearing).

2. 2

   2. Measure the actual motor current with a clamp-on ammeter and compare it to the soft starter's display and the motor's nameplate FLA.

3. 3

   3. Verify the motor's full load current (rAt parameter) and underload threshold (ULd parameter) in the soft starter settings for accuracy.

4. 4

   4. Check process conditions (e.g., tank levels, valve positions, pump suction) to ensure the motor has adequate mechanical load.

5. 5

   5. If current sensing is suspected, compare current readings from individual phase current transformers (CTs) within the soft starter (if accessible).