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MELSEC-Q
8 EMC AND LOW VOLTAGE DIRECTIVE
8.2.3 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; category IV has the highest durability.
Category III Category II Category ICategory IV
Figure 8.1: 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.
8.2.4 Control box
Because the PLC is an open device (a device designed to be stored within another
module), be sure to use it after storing in the control box.
(1) Electrical shock prevention
In order to prevent persons who are not familiar with the electric facility such as
the operators from electric shocks, the control box must have the following
functions :
(a) The control box must be equipped with a lock so that only the personnel who
has studied about the electric facility and have enough knowledge can open it.
(b) The control box must have a structure which automatically stops the power
supply when the box is opened.
(2) Dustproof and waterproof features
The control box also has the dustproof and waterproof functions. Insufficient
dustproof and waterproof features lower the insulation withstand voltage, resulting
in insulation destruction. The insulation in our PLC is designed to cope with the
pollution level 2, so use in an environment with pollustion level 2 or below.
Pollution level 1 : An environment where the air is dry and conductive
dust does not exist.
Pollution level 2 : An environment where conductive dust
does not usually exist, but occasional temporary
conductivity occurs due to the accumulated dust. Generally,
this is the level for inside the control box equivalent to IP54
in a control room or on the floor of a typical factory.
Pollution level 3 : An environment where conductive dust exits and conductivity
may be generated due to the accumulated dust.
An environment for a typical factory floor.
Pollution level 4 : Continuous conductivity may occur due to rain, snow,
etc. An outdoor environment.
As shown above, the PLC can realize the pollution level 2 when stored in a
control box equivalent to IP54.