14 
 
3.2.3 Power supply 
The insulation specification of the power module was designed assuming 
installation category II. Be sure to use the installation category II power supply to 
the programmable controller. 
The installation category indicates the durability level against surge voltage 
generated by a thunderbolt. Category I has the lowest durability; category IV has 
the highest durability. 
Category III Category II Category ICategory IV
 
Figure 1.: Installation Category 
Category II indicates a power supply whose voltage has been reduced by two or 
more levels of isolating transformers from the public power distribution.