This part of IEC60721 provides guidance on the use of all parts of IEC60721-3. It contains background information including information on the application and limitation of the classes given in various parts of IEC60721-3 which can be used in the design, limitation of conditions and protection of equipment.
Reference to IEC60721-3-0 is important in order to avoid misuse of the classes defined in the other parts of IEC60721-3.