FANUC Alarm 306 — Servo Overheating

What This Fault Means

Alarm 306 (OVH) triggers when the servo motor's built-in thermal sensor detects excessive temperature. The axis is disabled to prevent motor demagnetization and winding damage.

Common Causes

• Continuous operation at or near maximum torque
• Machine cutting parameters too aggressive (feed rate, depth of cut)
• Servo motor cooling fan failed or blocked
• Axis mechanical resistance too high (tight gibs, contaminated ways)
• Ambient temperature in the machine enclosure too high

Recommended Fix

1. Let the motor cool — alarm will auto-clear when temperature drops.
2. Check the servo motor cooling fan if equipped.
3. Reduce cutting parameters (lower feed rate, reduce depth of cut).
4. Lubricate the axis ways and check gib adjustment — excessive tightness increases motor effort.
5. If the alarm trips during light cuts, the motor may need replacement (demagnetized magnets).