Siemens · SINAMICS G120
The motor holding brake control is malfunctioning, posing a risk of uncontrolled motor movement. This can stem from an incorrect p1278 setting, disconnected or interrupted brake cables, a ground fault, or a short-circuit in the brake winding. A fault in the Safe Brake Relay, Control Unit, or Power Module could also be the cause.
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Verify the setting of parameter P1278 (Brake control mode) according to the motor's technical specifications and the application's requirements.
Measure the resistance of the motor brake coil directly at the drive's brake terminals (e.g., X11/X12) to compare with the specified value (e.g., 20-50 Ohms).
Check for 24VDC or 400VAC (depending on brake type) output voltage at the brake terminals when the drive commands brake release (e.g., using a multimeter).
Inspect the entire brake cabling path from the drive to the motor for signs of physical damage, loose connections, or insulation breakdown.
Perform an insulation resistance test (Megger test) on the brake cables and motor brake coil to detect ground faults.