Zone II

Reference Documents: 60079-15 (Equipment protection by type of protection ‘n’)

SCOPE: IEC 60079-15 is applicable to:

Non-sparking electrical equipment
Equipment having parts or circuits producing arcs or sparks
Equipment having hot surfaces
Equipment having combination of hot surfaces and arc-producing parts

And if these equipment are not protected in one of the ways specified in this standard, then a surrounding explosive gas atmosphere could be ignited.

Official Definition: Type of protection applied to electrical equipment such that, in normal operation and in certain specified expected occurrences, it is not capable of igniting a surrounding explosive gas atmosphere.

(Malfunctions causing ignition are not allowed, however “expected occurrences” such as a failed lamp in a light fixture are allowed)

DOMAIN of Ex n

1. Non-sparking Device nA (no longer covered by IEC 60079-15)

Non-sparking Device nA : Device constructed to minimize the risk of occurrences of arcs & sparks capable of creating an ignition hazard during normal operation.

As per IEC 60079-15 Edition No. 5 (2017) .This type of protection nA is now designated as type of protection ec , and all the relevant requirements are now based on IEC 60079-7 (2015)

2. Enclosed Break Device nC (no longer covered by IEC 60079-15)

The new nC (Modified ) domain

The simple meaning of the above diagram is as follows :
The components & parts which in normal operation produces ARCS, SPARKS or HOT SURFACES and would certainly ignite a surrounding explosive atmosphere are prevented from interacting and ignition by one or more (Combination) of the methods described as:

Hermetically Sealed Device
Non-Incendive Components
Sealed Device
Restricted Breathing Enclosure .

3. Restricted -Breathing Enclosure ‘nR’

An enclosure that is designed to restrict the entry of gases , vapours and mists.

The different types of protection techniques being defined under the main heading of Ex n , tends to cover the maximum aspects of the involved equipment .

It would be best ,for the sake of understanding & clarity , to remember the following definitions :-

Device :Material element or assembly of such elements intended to perform a required function

Component : Constituent part of a device which cannot be physically divided into smaller parts without losing its particular function

nC (Sealed-device) deals with the device as a whole which, due to its special construction cannot be opened during normal service and is sealed effectively against the ingress of the external (surrounding ) atmosphere

nC (Hermetically-sealed Device) deals with the device as a unit and give details of the construction which based upon the principle of ISOLATION (rather Complete Isolation) by Hermetically sealing the device, permanently, from the external atmosphere by soldering , brazing welding or fusion.

nC ( non-incendive component) deals with the components ,having electrical contacts, making & breaking type , which does not cause ignition of the surrounding atmosphere , by virtue of the design of the operating mechanism & construction of the same.

nR (Restricted-breather enclosure) deals with the device as a whole , with emphases on the ENCLOSURE , (no details of the devices & components inside ) so constructed so as to restrict the BREATHING of the enclosure. Breathing is exchange of the inner & outer atmosphere across the boundary of the enclosure

Equipment Grouping & Temperature Classes are same as specified in IEC 60079-0

Traditionally Equipment Protection by type of protection ‘n’ is associated with Zone 2.

However the choice of the equipment for installation in Zone 2 areas is vast as far as EPL (Equipment Protection Level) is concerned.

The design engineer is free to use following EPL:-

Ga Gb Gc (For explosive Gas)

Da Db Dc (For explosive Dust or Flammable Fibers- Zone 22 )

….And the EPL of nA, nC & nR is Gc

Thus the final decision should be the state-of the art BLEND of :-