Cause : Mains Phase Missing comes when one or more of the mains input phases is missing or has a significant voltage imbalance.

The F0020 fault in Siemens Micromaster 440 indicates a missing phase from the supply voltage. This means the drive isn't detecting all three phases of the incoming power supply.

Here are some steps to diagnose and resolve this issue:

1. Check Mains Supply:

   • Verify that the incoming mains supply is present on all phases (L1, L2, and L3).
   • Use a multimeter to measure the voltage between phases to ensure they are within the specified range.

2. Inspect Connections:

   • Ensure that all power connections are secure and properly tightened.
   • Check for any signs of loose connections, damaged cables, or burned terminals.

3. Check Input Fuses/Breakers:

   • Verify that all input fuses or circuit breakers are intact and not tripped.
   • Replace any blown fuses or reset tripped breakers as necessary.

4. Measure Voltage Balance:

   • Confirm that the voltage levels between the phases are balanced. A significant imbalance can trigger this fault.
   • The voltage difference between phases should be minimal.

5. Inspect Supply Quality:

   • Check the quality of the mains supply. Ensure there are no significant fluctuations or drops in voltage.
   • Investigate any potential sources of electrical noise or interference that could affect the inverter.