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Distribution in low-voltage installations

External influences shall be taken into account when choosing: b The appropriate measures to ensure the safety of persons (in particular in special locations or electrical installations) b The characteristics of electrical equipment, such as degree of protection (IP), mechanical withstand (IK), etc. | E - Distribution in low-voltage installations 3 External influences IEC 60364-5-51 External influences shall be taken into account when choosing The appropriate measures to ensure the safety of persons in particular in special locations or electrical installations The characteristics of electrical equipment such as degree of protection IP mechanical withstand IK etc. 3.1 Definition and reference standards Every electrical installation occupies an environment that presents a variable degree of risk For people For the equipment constituting the installation Consequently environmental conditions influence the definition and choice of appropriate installation equipment and the choice of protective measures for the safety of persons. The environmental conditions are referred to collectively as external influences . Many national standards concerned with external influences include a classification scheme which is based on or which closely resembles that of international standard IEC 60364-5-51. E25 If several external influences appear at the same time they can have independent or mutual effects and the degree of protection must be chosen accordingly 3.2 Classification Each condition of external influence is designated by a code comprising a group of two capital letters and a number as follows First letter A B or C The first letter relates to the general category of external influence A environment B utilisation C construction of buildings Second letter The second letter relates to the nature of the external influence. Number The number relates to the class within each external influence. Additional letter optional Used only if the effective protection of persons is greater than that indicated by the first IP digit. When only the protection of persons is to be specified the two digits of the IP code are replaced by the X s. Example IP XXB. Example For example the code AC2 signifies A environment AC environment-altitude AC2 environment-altitude 2 000 m 3.3 List of .