Chapter 14 Fault CodesMS300 
556 
 
Over-voltage during 
constant speed   
(ovn) 
DC bus over-voltage at constant speed. 
When ovn occurs, the drive closes the gate of the 
output immediately, the motor runs freely, and the 
display shows an ovn error. 
230V models: 410 V
DC
 
460V models: 820 V
DC 
575V models: 1116 V
DC
 
Immediately act when the DC bus voltage is higher than the level 
Fault Treatment Parameter 
Reset only when the DC bus voltage is lower than 90% of the over-voltage level 
Impulsive change of the load 
1.  Connect the brake resistor, braking unit or DC bus to the drive. 
2.  Reduce the load. 
3.  Replace the drive with a larger capacity model. 
4.  Adjust the braking level (Pr.07-01 or bolt position of the brake unit). 
The setting for stall prevention 
level is smaller than no-load 
current 
The setting of the stall prevention level should be larger than no-load current 
Regenerative voltage of motor 
inertia 
Use over-voltage stall prevention function (Pr.06-01) 
Use a braking unit or DC bus 
Power voltage is too high 
Check if the input voltage is within the rated AC motor drive input voltage range, 
and check for possible voltage spikes. 
ON/OFF switch action of phase-in 
capacitor in the same power 
system 
If the phase-in capacitor or active power supply unit acts in the same power 
system, the input voltage may surge abnormally in a short time. In this case, 
install an AC reactor. 
The ground short circuit current charges the capacitor in the main circuit 
through the power. Check if there is ground fault on the motor cable, wiring box 
and its internal terminals. 
Troubleshoot the ground fault. 
Incorrect wiring of brake resistor or 
brake unit 
Check the wiring of the brake resistor or braking unit. 
Malfunction caused by 
interference 
Verify the wiring of the control circuit and the wiring/grounding of the main 
circuit to prevent interference.