Ex-pert Electrical Technologies

Dynamic elaboration on the Art & Science of Hazardous Area Protection

Zone II

Zone 2

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

SCOPE: IEC 60079-15 is applicable to:

  1. Non-sparking electrical equipment
  2. Equipment having parts or circuits producing arcs or sparks
  3. Equipment  having hot surfaces
  4. 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  n

1. 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.

Types of Ex n

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:

  • Enclosed Break Device
  • 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 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 :-

  • Protection
  • Safety
  • Economics
  • Outage-free operation

(the list is certainly not complete . The innovative inventor will always add to this list.)

MARKING

Examples of Marking are as follows:-

  1. Ex nA d IIB T3 Gc

-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


A graphic representation

Zone 2 Protection basket

ZONE II Protection Basket


Zone2 new entrance

top

Information

This entry was posted on October 29, 2012 by in Uncategorized.
%d bloggers like this: