Code 230021: <location>Power unit: Ground fault
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>Power unit: Ground fault 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: %1 Drive object: All objects Reaction: OFF2 Acknowledge: IMMEDIATELY Cause: Power unit has detected a ground fault. - ground fault in the power cables - winding fault or ground fault at the motor. - CT defective. Additional cause for CU310/CUA31: - when the brake is applied, this causes t he hardware DC current monitoring to respond. Additional cause for parallel sw itching devices (r0108.15 = 1): - the closed-loop circulating current control is either too slow or has been set too fast. Fault value (r0949, interpret decimal): Absolute value, summation current [32767 = 271 % rated current]. Remedy: - check the power cable connections. - check the motor. - check the CT. The following applies addi tionally for CU310 and CUA31: - check the cables and contacts of the br ake connection (a wire is possibly broken). For parallel switching devices (r0108.15 = 1) the following additionally applies: - check the ground fault monitoring thresholds (p0287). - check the setting of the closed-loop circulating current control (p7036, p7037). See also: p0287 (Ground fault monitoring thresholds)
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 230021 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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