IEC 60917-1:2019 is available as IEC 60917-1:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 60917-1:2019 specifies the relationships between equipment practices and the modular order which are applicable to the main structural dimensions of electronic and electrical equipment mounted in various installations where dimensional interfaces have to be considered for mechanical compatibility. This document also established terms for parts and assemblies of mechanical structures for electrical and electronic equipment, to clarify the specific relations between equipment practices and modular order. This second edition cancels and replaces the first edition published in 1998 and its Amendment 1:2000. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) added information on newly developed detail specification standards of mechanical structures for the electrical and electronic equipment practices; b) added information on newly developed performance test standards for the verifications of environmental performances and safety aspects and issues of the thermal performance and thermal management for the electrical and electronic equipment practices; c) introduced the relations between the mechanical structure for electrical and electronic system, the verification of environmental performance and safety aspects and issues of the thermal performance and thermal management for the electrical and electronic equipment practices. Key words: IT Cabinets, Mechanical Structures