Cause : input phase loss comes when when one of the three phases of the incoming power supply to a delta drive is interrupted or disconnected. The cause of this fault is one of the input phases from the power grid or supply may be missing or unstable.

"input phase loss" fault in drive indicates that one or more of the input power phases are missing, unbalanced, or unstable. This means one of the three input phases is lost or becomes unbalanced, the drive will trigger this fault to protect itself and the connected motor.

Potential Causes of Input Phase Loss Fault:

1. Power Supply Issues:

   • One of the input phases from the power grid or supply may be missing or unstable.
   • Voltage fluctuations or phase imbalance can also trigger this fault.

2. Blown Fuse or Breaker:

   • A fuse or circuit breaker protecting one of the input phases could have blown or tripped, leading to a loss of that phase.

3. Loose or Damaged Wiring:

   • Loose connections or damaged cables on the input side of the drive can cause a phase to be missing.

4. Transformer Issues:

   • If the drive is connected to a transformer, issues with the transformer (e.g., a blown winding) could lead to phase loss.

5. Drive Rectifier Issues:

   • Internally, the drive’s rectifier section may be malfunctioning and unable to properly convert AC power to DC, leading to a perceived phase loss.

Troubleshooting Steps:

1. Verify Input Power:

   • Use a multimeter to check the voltage across all three phases at the drive input. Verify that all phases are present and the voltage is within the specified range.
   • If there’s a significant voltage drop or one phase is missing, contact your electrical utility or check the power source.

2. Check Fuses and Breakers:

   • Inspect the fuses or breakers on the input side of the drive. If a fuse has blown or a breaker has tripped, replace or reset it, but make sure to identify and resolve the underlying cause first.

3. Inspect Wiring:

   • Ensure that all connections on the input side are tight and secure.
   • Check for any damaged cables that may cause intermittent contact or phase loss.

4. Check for Phase Imbalance:

   • Use a meter to check for phase imbalances. A significant difference in voltage between phases may indicate a problem with the power supply.

5. Check Transformer (if applicable):

   • If a transformer is involved, ensure it’s operating correctly. Test the windings for continuity and check for any internal damage.

6. Reset the Drive:

   • Once the issue has been resolved, reset the drive and monitor it to ensure the fault doesn’t recur.

7. Monitor Input Conditions:

   • Some Delta drives allow you to monitor the input voltage and phase conditions through their diagnostic menus. Check the drive's diagnostics for more specific information on the fault.