- The energy fed back into the DC bus by the machine mechanics during braking was so high that it could not be dissipated by the supply unit within the feed back time. This caused the DC bus voltage to rise to an impermissible value.
- No braking resistor connected or connection or cable faulty.
- F8xxx error at high speeds (field weakening area) on a synchronous motor.
- Device fault on the supply unit (error in the DC bus voltage measurement)