46
5  TROUBLESHOOTING
Only authorized personnel should be permitted to perform maintenance and 
inspections or replace parts.
No. Fault Status Cause Corrective Action
1
Braking resistor 
unit overload relay 
(or thermal over-
load protector) trips 
when not decelerat-
ing.
• Without braking unit
Inverter built-in main circuit dis-
charging transistor short circuited
Replace the inverter.
• With braking unit
Braking unit main circuit discharg-
ing transistor short circuited
Replace the unit.
Improper braking unit power supply 
voltage selection connector setting
(Power supply voltage > power sup-
ply voltage selection position)
Set it again.
2
Inverter trips at 
overvoltage (ov).
Insufficient braking resistor unit 
capacity
Examine the braking 
conditions again.
Improper wiring Check and repair.
Braking unit fault Replace the unit.
3
Braking resistor 
unit overload relay 
(or thermal protec-
tor) sometimes 
trips.
Insufficient braking resistor unit 
capacity
Examine the braking 
conditions again.
4
Braking unit trips 
by heat sink over-
heat.
Excessive start/stop switching fre-
quency
Examine the operat-
ing conditions again.
Excessive load inertia
Improper combination of braking 
unit and braking resistor unit
Reset.
Ambient temperature 104°F (40°C) Reduce it.
Braking unit fault Replace the unit.
5
The fault contact of 
a braking unit 
instantaneously 
turned ON when 
the power was 
turned ON.
Neither a braking resistor nor a 
braking resistor unit is connected to 
the braking unit.
Connect a braking 
resistor or braking 
resistor unit to the 
braking unit.