This European Standard specifies the particular requirements for construction, testing and marking of electrical apparatus of equipment group II, conformity Category 1 G as defined in EN 50014:1997. Such apparatus comprises equipment designed to be capable of functioning in conformity with the operational parameters established by the manufacturer and ensuring a very high level of protection. Category 1 G apparatus is intended for use in hazardous areas, in which potentially explosive atmospheres caused by mixtures of air and gases, vapours or mists under normal atmospheric conditions (temperature = -20 °C to +60 °C, pressure = 0,8 bar to 1,1 bar) are present continuously, for long periods or frequently. This standard also applies to apparatus mounted across the boundary between hazardous and less hazardous areas where Category 1 and Category 2 equipment may normally be installed, respectively, for example in the wall of a storage vessel. This standard also makes provision for apparatus installed outside the hazardous area, but electrically connected to apparatus of Category 1 within the hazardous area (associated apparatus).This standard supplements the requirements of EN 50014 to EN 50020 and EN 50028 to adapt the level of safety provided by those standards to the very high level of risk. NOTE: In designing apparatus for operation in a potentially explosive atmosphere under conditions other than the atmospheric conditions given above, this standard may be used as a guide. However, additional testing is recommended related specifically to the intended conditions of use. This is particularly important when the types of protection Flameproof enclosure (EN 50018) and Intrinsic safety (EN 50020) are applied