UnderVoltage

What does F4 mean?

This fault is triggered when the incoming AC line voltage drops below the drive's acceptable operating range. This can be caused by a sustained low voltage condition or a momentary power sag. This is an Auto-Reset/Run type fault configurable with parameters A092 and A093.

• Sustained low voltage condition from the utility grid or plant distribution system, below the drive's minimum operating voltage.
• Momentary power sag (voltage dip) caused by large loads starting elsewhere on the same electrical feeder.
• Incorrectly sized or failing input reactor or isolation transformer upstream of the drive, leading to excessive voltage drop.
• Loose connections at the drive input terminals (L1, L2, L3) or upstream protective devices causing voltage drop under load.
• End-of-life DC bus capacitors within the drive, reducing its ability to maintain stable DC bus voltage during minor dips.

Click steps to track your progress.

1. 1

   Measure the incoming AC line voltage (L1-L2, L2-L3, L3-L1 for 3-phase, L1-N for 1-phase) at the drive's input terminals and compare to drive specifications.

2. 2

   Monitor the DC bus voltage (often accessible via drive display) during operation to observe its behavior relative to the Undervoltage trip threshold.

3. 3

   Check the torque of the wiring connections at the drive's L1, L2, L3 input terminals and upstream disconnect.

4. 4

   Consult local power company or plant electrical staff regarding potential grid voltage instability or heavy load switching events.

5. 5

   If a sag is suspected, use a power quality analyzer to log input voltage over time to capture transient events.