Similar to Ex e, Ex n is fundamentally a non sparking concept.1
Its criteria is for Normal operating conditions and, in general, fault conditions do not need to be taken into consideration.
As there is no fault tolerance Ex n has an EPL Gc (Category 3G) with the protection only suitable for use in zone 2
Commonly referred to as non-sparking there are 3 basic methods of achieving compliance.
However the latest version 2017 has taken out Ex nA and Ex nC and put them into EN 60079-7 (Ex ec) and EN 60079-1 (Ex dc) respectively. Ex nA and Ex nC are still valid as the 2010 version of the standard has not been withdrawn.
There still exists some equipment certified Ex nl (non-incendive), it was rarely used as a concept, cannot not be used for any new installtions and it is recomended that older equipment be replaced where practicable.
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Ex nA – traditional non-sparking (See Ex ec) Traditional one of the easiest protection methods for equipment to be used in Zone 2 Ex nA is gradually being replaced by Ex ec which is slightly easier to meet.
All components must be certified unless a competent person (i.e. the person issuing the certification) includes justification within the technical file, some simple components are obviously non-sparking e.g. resistors fitted in a terminal and a declaration may be sufficient in lieu of formal certification.
Heat dissipation of the component will also need to be considered. -
Ex nC – enclosed break (See Ex dc) As Ex nA with the addition of any sparking components (e.g. switches) hermetically2 sealed so the sparking element is protected. Components should be certified as for Ex nA but it is less likely that a basic declaration would be sufficient as the hermetically sealed component aspect is not so obvious and generally the technical file should include independent certification as justification for use.
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EX nR – restricted breathing, generally an assembly whereby the enclosure is sealed preventing the ingress of gas. This allows uncertified components to be used internally. However, components which go through the enclosure wall and therefore come in contact with any gas should be suitably certified. The sealing is not a hermetic seal per se but stringent requirements requiring the enclosure to be pressure tested for leaks.
Notes
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Ex nR restricted breathing based on a sealed enclosure, it does allow the potential for sparking internally but is designed to keep the the gas out of the enclosure in normal use. ↩
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An Hermetically sealed device is so constructed that the external atmosphere cannot gain access to the interior and in which any seal is made by fusion, for example, brazing, welding or the fusion of glass to metal ↩