Siemens alarm 400252: Error in internal communication with NCK
SINUMERIK PLC system alarm · Siemens 840D/810D powerline
What it means
An error occurred during data transmission between the PLC and the NCK over their internal interface. Siemens documents this specifically for FM-NC configurations, where the NC function runs as an FM module and talks to the S7 CPU across the backplane. A restart of the NCK is prescribed; repeated occurrence indicates a hardware-level bus problem.
Likely causes
- Interruption of internal NCK-to-CPU transmission (FM-NC)
- Seating/contact problem of the FM-NC module or backplane connector
- Transient system error cleared by restart
Triage note: (FM-NC only). Companion alarms 400255/400256/400257 report the same conditions for the second NCK (NCK2) in dual-NCK systems.
Need the part urgently?
Send us alarm 400252 with your machine details — typical RFQ turnaround is 24–48h.