Definition and reference standards
From Electrical Installation Guide
External influences shall be taken into account when choosing:
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.