Applicable Systems
Series 0i
Series 16/18/21
Alpha
Beta
Symptoms
The axis has reached the software overtravel limit in the positive (+) direction. Alarm OT 520 is displayed for the Z axis.
Possible Causes
- Z axis moved beyond the physical or software travel limit
- Z axis overtravel limit switch activated
- Program error commanding axis beyond travel range
- Work coordinate or tool offset error causing overtravel
Troubleshooting Steps
- Step 1: Identify which axis triggered the overtravel alarm (Z)
The Z axis overtravel alarm is confirmed on the screen - Step 2: Switch to jog mode and move the Z axis in the opposite direction away from the limit
The axis moves away from the limit and the alarm can be reset - Step 3: Press RESET to clear the overtravel alarm
Alarm clears after axis is moved to a safe position - Step 4: Review the program or offset data that caused the overtravel
The problematic block or offset is identified and corrected
How to Reset
Move the axis away from the limit switch in the opposite direction, then press RESET to clear the alarm. For software overtravel, check and correct the travel limit parameters.
Frequently Asked Questions
- Q: What does Fanuc OT 520 Z alarm mean?
Overtravel (+) Soft: The axis has reached the software overtravel limit in the positive (+) direction. This indicates the Z axis has traveled beyond its allowed range.
- Q: How do I clear Fanuc overtravel alarm 520?
Switch to jog/handwheel mode, move the axis away from the limit in the opposite direction, then press RESET. If the axis cannot move, use the overtravel release switch (if equipped).
Source: Fanuc 0i/0iMate Overtravel Alarm Code List, FANUC Corporation
Category: CNC