0858

Common Causes

• Inverter unit internal fault
• Sustained overload operation driving excessive motor cable current
• Poor inverter cooling (blocked heatsink/airflow) allowing temperature to climb under load

Troubleshooting Steps

1. 1Read the code number shown with the alarm: code 1 = Fixed code: inverter detected excessive motor cable current and abnormal internal temperature rise
2. 2Let the inverter unit cool, then note when the alarm occurs: if it appears only during heavy cutting or rapid cycling, reduce the load/duty (lighter cuts, lower accel duty) and see if the alarm stays away — this points to overload operation.
3. 3Check the inverter unit's cooling path: clear dust and chips from the heatsink and vents and confirm the cooling fans run.
4. 4Before touching the drive, power down, lock out, and wait for the DC bus to fully discharge — inverter capacitors hold lethal voltage after power-off.
5. 5Inspect the motor cable and its connectors for damage, partial short or poor contact that could cause excessive current draw.
6. 6If the alarm returns at light load with cooling and cabling confirmed good, the inverter unit itself is suspect; record the alarm number and object and contact Okuma service for unit replacement.