This International Standard applies to interfaces between low-voltage switchgear, controlgear, and controllers (e.g. programmable controllers, personal computers, etc.). This document does not apply to higher level industrial communication networks that have become known as fieldbuses and are considered by IEC subcommittee 65C. The purpose of this document is to harmonize and define rules, components and requirements of a general nature applicable to industrial CDIs. Those features of the various CDI standards which can be considered as general have therefore been brought together in this part of IEC 62026. For each CDI, two main documents are necessary to determine all requirements and tests: a) this document, referred to as IEC 62026-1 in the relevant CDI parts covering the various types of CDIs; b) the specific CDI part of the IEC 62026 series. A specific CDI part may omit a general requirement if it is not applicable, or it may add to it if it is inadequate in the particular case, but it should not deviate from the requirement unless there is substantial technical justification. NOTE Product-specific requirements for products incorporating a CDI are given in the relevant product standards. These requirements apply in addition to those given in this document.