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.
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 equipments .
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
nA (non-sparking device) deals with the Device as a unit without any details of the ways to achieve the safety level of non-occurrence of sparks & arcs during normal operation .
nC (Enclosed-break device ) goes one step further and deals with a Special Device which incorporates ELECTRICAL CONTACTS, making & breaking and strong enough to withstand the pressure of any explosion caused by the entry of flammable gas . Enclosed-break device does not transfer the effects of the internal explosions to the outer atmosphere .
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
ZONE II Protection Basket