Code 206351: <location>Infeed: Measured line frequency too low
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>Infeed: Measured line frequency too low alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Message value: Line frequency: %1 Drive object: A_INF, S_INF Reaction: NONE Acknowledge: NONE Cause: The actual line frequency f_line is lower than the parameterized alarm threshold (f_line < p0211 * p0285). The alarm can be output in two operating states: 1. During the power-on phase of the infeed unit. Consequence: Synchronization of the infeed to the line supply is interrupted and is restarted. 2. While the infeed is operational. Consequence: The infeed remains in the operating (run) state and al arm A06351 is output. This signifies a critical operational fault. Alarm value (r2124, floating point): Current line frequency determined. See also: p0285 (Line supply frequency undershot, alarm threshold) SINAMICS-Alarms Remedy: - check the parameterized line frequency and if required change (p0211). - check the alarm threshold (p0285). - check the line supply. - check the line supply quality. See also: p0211 (Rated line freq), p0285 (Line supply frequency undershot, alarm threshold)
Source: SINUMERIK 840D sl / 840Di sl / SINAMICS S120 Diagnostics Manual (DAsl, 03/2009)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Siemens SINUMERIK 840D CNC Alarms
Siemens controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 206351 on the SINUMERIK 840D CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Siemens's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4014 Siemens SINUMERIK 840D CNC codes.
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