Cause : UCE lower switch/UCE Phase L2 comes when there was an UCE shutdown in phase L2. This fault signifies an issue with the inverter's ability to control the voltage or current on that specific phase during operation.

The fault F026 in a Siemens Masterdrive indicates a problem with the output phase. The specific phase will be denoted after the fault code, for example, F026-L2 signifies an issue with phase L2. This fault essentially means there's a problem with the power delivered to the motor on a specific phase.

1. Phase L2 for short-circuit or ground fault.
2. Check the converter outputs for earth fault.
3. Check the CU is correctly inserted.