SINAMICS G120 CU240E-2 F07801 at start, what to check first?
I'm getting an F07801 fault on my SINAMICS G120 CU240E-2 drive when starting a fan. It trips right at the beginning of the start sequence. What's the most likely cause and what should I check first?
The F07801 fault on a SINAMICS G120 drive indicates that the permissible motor limit current was exceeded. This often occurs at start, during acceleration, or on a load step. Common causes include switching onto a rotating motor, a ramp-up that is too short, or incorrect current limit settings. The specific timing of the fault can help narrow down the cause.
Likely causes and checks
1Switching onto a rotating motor
- Points to it
- If the motor is still rotating (freewheeling) when the drive attempts to start, it can cause an overcurrent condition if the flying restart function is not enabled or properly configured.
- Check
- Check if parameter p1200 (flying restart) is enabled. If the trip only occurs when restarting a coasting load, enabling this function is the primary remedy.
2Ramp-up too short or load too high (U/f operation)
- Points to it
- If the acceleration ramp is too short for the connected load, the motor may draw excessive current during acceleration, leading to an overcurrent trip.
- Check
- Increase the ramp-up time by adjusting parameter p1120 or reduce the motor load if possible. This is particularly relevant if the fault occurs partway through acceleration.
3Current limit or controller settings are incorrect
- Points to it
- An incorrectly set current limit or current controller parameters can cause the drive to trip prematurely, even under normal operating conditions.
- Check
- Verify the current limit setting in p0640. If using vector control, check p1715/p1717. In U/f operation, review parameters p1340–p1346. Also, check if alarm A07409 (U/f current limiting controller active) appears before the trip.
4Motor data or star/delta connection is wrong
- Points to it
- Incorrect motor data entered during commissioning or an improper star/delta connection can lead to the drive miscalculating motor current and tripping on overcurrent.
- Check
- Confirm that the motor connection (star/delta) matches the drive's configuration and that the motor rating plate data entered during commissioning is accurate. This is especially relevant if the trip occurred after a motor or converter change.
Next check: Given the fault occurs right at the beginning of the start sequence on a fan (which can freewheel), the first thing to check is whether the drive is attempting to start onto a rotating motor and if the flying restart function (p1200) is enabled.
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