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20. EMC AND LOW VOLTAGE DIRECTIVES
20.2.3 Power supply
The insulation specification of the power supply module was designed assuming
installation category II. Be sure to use the installation category II power supply to the PLC.
The installation category indicates the durability level against surge voltage generated by
a thunderbolt. Category I has the lowest durability; and category IV has the highest
durability.
Category II indicates a power supply whose voltage has been reduced by two or more
levels of isolating transformers from the public power distribution.
Fig. 20.1 Installation category
Category IV Category III Category II Category I
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