Dynamic elaboration on the Art & Science of Hazardous Area Protection
Reference Documents: 60079-15 (Equipment protection by type of protection ‘n’)
SCOPE: IEC 60079-15 is applicable to:
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.
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:
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 :-
(the list is certainly not complete . The innovative inventor will always add to this list.)
Examples of Marking are as follows:-
-20°C ≤ Ta ≤ +60° C
Certificate No: 12345FG X
Its a non-sparking equipment incorporating a flame-proof component for ambient temperature range of -20 to +60°C with specific conditions of use
nA : non-Sparking Equipment
d : flame-proof component
IIB : Gas Group
Gc : EPL
12345FG X: X indicates the special conditions of use
2. Ex nR IIC Gc
Certificate No: 7865 U
Its a restricted breathing enclosure as a component
Traditionally Ex n consisted of following EPLs :-
During the past years, IEC has shifted the following EPLs from the domain of Ex n (IEC 60079-15) to others , as specified below :-
Ex nA non-sparking device is now Ex ec
Ex nC enclosed break device is now Ex dc
Ex nC Encapsulated device is now Ex mc
Ex nL Energy Limited is now Ex ic
Ex nZ Simplified Pressurization is now Ex pz