IEC 60422:2013 gives guidance on the supervision and maintenance of the quality of the insulating oil in electrical equipment. This International Standard is applicable to mineral insulating oils, originally supplied conforming to IEC 60296, in transformers, switchgear and other electrical apparatus where oil sampling is reasonably practicable and where the normal operating conditions specified in the equipment specifications apply. This International Standard is also intended to assist the power equipment operator to evaluate the condition of the oil and maintain it in a serviceable condition. It also provides a common basis for the preparation of more specific and complete local codes of practice. The standard includes recommendations on tests and evaluation procedures and outlines methods for reconditioning and reclaiming oil and the decontamination of oil contaminated with PCBs. This fourth edition cancels and replaces the third edition, published in 2005, and constitutes a technical revision. The main changes with respect to the previous edition are as follows: - This new edition represents a major revision of the third edition, in order to bring in line this standard with latest development of oil condition monitoring, containing new limits for oil parameters, suggested corrective actions in the tables and new test methods. - The action limits for all oil tests have been revised and changes made where necessary to enable users to use current methodology and comply with requirements and regulations affecting safety and environmental aspects. - In addition, this standard incorporates changes introduced in associated standards since the third edition was published.