Fanuc 0i Error Code OT 521 4th

Fanuc CNC Minor Overtravel Alarm

Model: FANUC Series 0i / 0i Mate (Overtravel) | Code: OT 521 4th

Applicable Systems
Series 0i Series 16/18/21 Alpha Beta

Symptoms

The axis has reached the software overtravel limit in the negative (-) direction. Alarm OT 521 is displayed for the 4th axis.

Possible Causes

  • 4th axis moved beyond the physical or software travel limit
  • 4th axis overtravel limit switch activated
  • Program error commanding axis beyond travel range
  • Work coordinate or tool offset error causing overtravel

Troubleshooting Steps

  1. Step 1: Identify which axis triggered the overtravel alarm (4th)
    The 4th axis overtravel alarm is confirmed on the screen
  2. Step 2: Switch to jog mode and move the 4th axis in the opposite direction away from the limit
    The axis moves away from the limit and the alarm can be reset
  3. Step 3: Press RESET to clear the overtravel alarm
    Alarm clears after axis is moved to a safe position
  4. 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 521 4th alarm mean?

    Overtravel (-) Soft: The axis has reached the software overtravel limit in the negative (-) direction. This indicates the 4th axis has traveled beyond its allowed range.

  • Q: How do I clear Fanuc overtravel alarm 521?

    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).

Related Fanuc Fault Codes

Source: Fanuc 0i/0iMate Overtravel Alarm Code List, FANUC Corporation

Category: CNC