Bracketed (III/3) refers to the surge voltage category / pollution level. Where
Surge voltage: refers to the power supply is turned on instantly, the peak voltage into the power supply equipment. Usually surge voltage type III, II, I, etc.;
Pollution level 3: conductive pollution, or due to condensation so that the dry non-conductive pollution into conductive;
Cooperative pollution level meaning:
Excerpted from the national standard GB 14048.1-2012 low voltage switchgear and control equipment, in order to facilitate the determination of electrical clearance and creepage distance, the micro-environment can be divided into four pollution levels:
Rank 1: no pollution or only dry non-conductive pollution.
Class 2: general situation only non-conductive pollution, but must take into account the occasional transient conductivity due to condensation.
Class 4: Persistent conductive contamination, e.g. due to conductive dust or rain or snow.
Standard pollution classes for industrial appliances:
Industrial appliances are generally suitable for use in pollution class 3 environments, unless otherwise specified in other relevant product standards. However, due to special uses and micro-environments can be considered to adopt other pollution levels.
Eg: The pollution level of the micro-environment of the appliance may be affected by the way the enclosure is installed.
Standard pollution levels for household and similar appliances:
Unless otherwise specified in other relevant product standards, household and similar appliances are generally used in pollution level 2 environments.
The above is for reference only, as for the maximum voltage that needs to be accessed you can refer to the terminal parameters, or ask the manufacturer!