This standard specifies the particular requirements for construction, test and marking for electrical apparatus of Group II intended for use in Class I, Zone 0 as defined in the National Electrical Code, ANSI/NFPA 70.

This electrical apparatus, within the operational parameters specified by the manufacturer, ensures a very high level of protection that includes rare faults related to the apparatus or two faults occurring independently of each other.

NOTE 1 A malfunction may result from a failure of the component parts of the electrical apparatus or from anticipated externally applied influences. Two independent malfunctions which may occur more frequently and which, separately, would not create an ignition hazard but which, in combination, could create a potential ignition hazard, should be regarded as occurring together to form a rare fault.

This electrical apparatus is intended for use in Class I, Zone 0 hazardous areas, in which explosive gas atmospheres caused by mixtures of air and gases, vapours or mists under normal atmospheric conditions are present continuously, for long periods or frequently.

This standard also applies to apparatus mounted across the boundary between Class I, Zone 0 and Class I, Zone 1.

EXAMPLE: In the wall of a storage vessel.

This standard also applies to apparatus installed outside Class I, Zone 0, but electrically connected to apparatus inside Class I, Zone 0 (associated apparatus).

This standard supplements the general requirements in ANSI/ISA-60079-0

NOTE 2 In designing apparatus for operation in explosive gas atmospheres under conditions other than the atmospheric conditions given in IEC 60079-0, 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' (ANSI/ISA-60079-1) and ‘Intrinsic safety' (ANSI/ISA- 60079-11) are applied.

NOTE 3 The classification of hazardous areas in zones is defined in the National Electrical Code.

NOTE 4 There may be other non-electrical sources of ignition (for example ultrasonic, optical or ionizing radiation) that are not addressed by this standard; these should also be taken into consideration (see, for example, EN 1127-1).