Cause : DC link voltage undervoltage comes when the power unit has detected an undervoltage condition in the DC link. When encountering a DC link voltage undervoltage fault with a Siemens drive, it indicates that the voltage level in the DC link has dropped below the acceptable threshold.

F003 fault code in a Siemens drive indicates an undervoltage condition. This means the voltage supplied to the drive is lower than the minimum required for proper operation.

Several factors can contribute to an F003 fault:

1. Main supply failure: A complete power outage or significant drop in the AC mains voltage feeding the drive can trigger this fault.
2. Loose or faulty connections: Loose or corroded connections in the power supply path to the drive can cause voltage drops and lead to an F003 fault.
3. Undersized supply: If the electrical supply feeding the drive is not rated for the current requirements of the motor and drive system, it might not be able to provide sufficient voltage during operation.
4. Phase failure: In a three-phase power system, a loss of voltage in one phase can also cause an F003 fault on the drive, even if the overall line voltage might appear normal.

Follow these steps to correct the fault:

1. Check Power Supply: Verify that the AC mains power is available and within the expected voltage range for the drive. Use a voltmeter to measure the voltage at the input terminals of the drive.
2. Inspect Connections: Ensure all power supply connections to the drive are secure and free from corrosion or damage. Tighten any loose connections.
3. Consult Drive Manual: Refer to the user manual for your specific Siemens drive model. It might provide additional troubleshooting steps specific to the F003 fault code and include information on parameters like the undervoltage threshold setting.