Ex n — the 'light' type of protection for zone 2 (IEC 60079-15)

The guide on ATEX & explosive atmosphere zones — classification and inspection covers the classification into zone 0, 1 and 2 (gas) and zone 20, 21 and 22 (dust). This article looks in more detail at one specific type of protection developed exclusively for the least hazardous gas zone: Ex n, standardised in IEC 60079-15.

Why zone 2 justifies its own, lighter type of protection

Zone 2 is the gas zone where an explosive atmosphere is unlikely during normal operation, and if it does occur, persists only briefly and rarely (for example due to a rare leak or fault). This contrasts sharply with zone 1, where an explosive atmosphere is expected occasionally during normal operation, and zone 0, where it is present continuously or for long periods. Because the probability of an explosive atmosphere in zone 2 is low, the required protection level of the equipment can correspondingly be lower — and therefore simpler and cheaper — than for Ex d (flameproof enclosure), Ex e (increased safety) or Ex i (intrinsic safety), which are usually also certified for zone 1 and sometimes zone 0.

The main Ex n sub-types

IEC 60079-15 distinguishes several techniques that each, in their own way, prevent equipment from becoming a source of ignition, all under the common label "type n":

Ex nA (non-sparking apparatus): equipment that produces no sparks, arcs, or dangerously hot surfaces during normal operation — the simplest and most common variant, suitable for example for motors and luminaires without switching contacts.
Ex nC (enclosed break contacts): equipment that does contain sparking contacts (such as a relay or switch), but where those contacts are housed in an enclosure that prevents ignition of the surrounding atmosphere.
Ex nR (restricted breathing enclosure): an enclosure designed so that the exchange of gas between the internal and external air is strongly limited, so that any internal ignition source cannot reach the external atmosphere within the time an explosive atmosphere could be present there.
Ex nL (energy limitation): a principle conceptually similar to intrinsic safety (Ex i, see the guide on Ex i entity parameters), but with less strict requirements, matching the lower risk level of zone 2.
Ex nP (pressurisation for zone 2): a lighter variant of the pressurisation principle also used for Ex p in zone 1 (see the guide on Ex p ignition protection by pressurisation), adapted to the lower requirements of zone 2.

The hard limit: Ex n must never be used in zone 0 or zone 1

The lower protection level of Ex n is justified solely by the lower probability of an explosive atmosphere in zone 2. Applying the same equipment in zone 1 (where an explosive atmosphere is expected periodically) or zone 0 (where it is continuously present) would raise the risk of actual ignition to an unacceptable level — Ex n equipment is therefore certified and usable exclusively for zone 2, never for zone 0 or zone 1.

Note: the EPL (Equipment Protection Level) associated with Ex n is Gc, the level that corresponds specifically to zone 2 — comparable to how the EPL marking on Ex d, Ex e and Ex i equipment (usually Gb or Ga) directly shows which zone the device is intended for. When in doubt, always check the EPL marking on the nameplate, not just the letter "n".

Why Ex n is often chosen in practice for zone 2

For equipment purchased specifically and exclusively for zone 2 — for example lighting, small motors, or control cabinets in a space classified as zone 2 because of a limited and rare leak risk — Ex n is often the most economically attractive choice: the construction requirements are less strict than for Ex d or Ex e, translating into a lower purchase cost and often a more compact, lighter enclosure, without this representing a safety compromise for that specific zone.

Practical relevance

When assessing equipment for a space classified as zone 2, it is important to check whether the applied device is actually intended for that zone, rather than being "over-specified" as an Ex d or Ex e device (which would be safe in itself but needlessly expensive), or, conversely, applied as Ex n equipment in a space that has meanwhile been reclassified as zone 1 — in the latter case the device no longer offers the required protection level.

Common mistakes

Applying Ex n equipment in zone 1 or zone 0, on the assumption that "Ex equipment is Ex equipment" — the type of protection must exactly match the zone classification.
Not checking the Ex n sub-type (nA versus nC versus nR versus nL versus nP), while each sub-type is designed for a different kind of ignition risk and they are not interchangeable.
Reclassifying a space from zone 2 to zone 1 (for example after a process change) without replacing the Ex n equipment present there with equipment offering a higher protection level.
Not checking the EPL marking (Gc) and relying only on the letter "n" on the nameplate, while the EPL unambiguously indicates the actual zone suitability.