IEC 60721-3-0:2020 provides guidance on the use of all parts of IEC 60721-3. It contains background information including information on the application and limitation of the classes given in various parts of IEC 60721-3 which can be used in the design, limitation of conditions and protection of equipment.This second edition cancels and replaces the first edition published in 1984 and Amendment 1:1987. This edition constitutes a technical revision.This edition includes the following significant technical changes with respect to the previous edition:a) This edition has been extensively simplified to only provide necessary information with regard to the process given in the other parts of IEC 60721-3 and information on class severity has been updated.