This part of IEC 61587 specifies seismic test requirements for chassis, subracks, and plug-in units as defined in the IEC 60297 and IEC 60917 series. It applies in whole or in part, only to the mechanical structures of chassis, subracks, and plug-in units for electronic equipment, according to the IEC 60297 and IEC 60917 series, and does not apply to electronic components, equipment or systems within the mechanical structures. NOTE Subracks may be an integral part of a chassis (often called in the industry a shelf or a crate). The object of this standard is to establish a level of physical integrity of chassis, subracks, and plug-in units according to IEC 60297 and IEC 60917 series that may provide a level of survivability that will preserve functionality during and after a seismic occurrence. It is intended to provide the user with a high level of confidence in the selection of an equipment practice to meet such needs. Since IEC 60297 and IEC 60917 series chassis, subracks, and plug-in units come in many sizes, weights and mechanical complexities, it is not possible to define a single minimum seismic test requirement for all weight categories. Therefore, overall mass categories are defined in this standard. However, the mass distribution inside a chassis and subrack is considered “application-specific” and herein defined as “intended use”. The single-axis or tri-axis acceleration for the seismic testing is selectable.