Scenario: A automotive paint line conveyor trips with F07902 every Monday morning but runs fine for the rest of the week.
Investigation: Technicians found no cable breaks. The motor windings tested OK. The clue was the timing – every Monday after weekend shutdown.
Root Cause: A magnetic contactor between the drive and motor had a pitted auxiliary contact that overheated slightly on the first start of the week, dropping one phase for 50ms. As the day progressed, thermal expansion improved contact – until the next Monday. siemens drive fault code 7902
Solution: Replaced contactor and implemented weekly starter torque check. Fault 7902 eliminated.
Open circuit → infinite ohms → fault 7902.
Short circuit → near 0Ω → fault 7902. Scenario: A automotive paint line conveyor trips with
Fault Code 7902 typically corresponds to:
"PROFIBUS: Cyclic connection failed" (or PROFINET equivalent, depending on the telegram type)
In SINAMICS firmware versions (e.g., V4.7+), 7902 indicates that the master-slave cyclic communication has been interrupted or never established. The drive is configured for fieldbus control (e.g., P0700 = 6 for PROFIBUS, or P0922 telegram selected) but no valid cyclic data exchange is occurring. Open circuit → infinite ohms → fault 7902
F07902: Motor overspeed The actual motor speed has exceeded the p2162 (overspeed threshold) value for longer than the time set in p2163.
Disconnect drive terminals and measure resistance at room temperature. Should be ~600Ω. Use a hairdryer to warm probe—resistance should increase smoothly.
To fix the problem permanently, you must identify why the phase failure occurred. Causes fall into four main categories: