Zone II and IEC 60079-15

Recalling some Basics

1. Explosive Atmosphere

Mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapour, or dust, fibres, or flyings which, after ignition, permits self-sustaining propagation

2. Hazardous Area

Aea in which an explosive atmosphere is present, or can be expected to be present, in quantities such that special precautions for the construction, installation and use of equipment are required

Explosive gas atmosphere is mixture with air, under atmospheric conditions, of flammable substances in the form of gas or vapour, which, after ignition, permits self-sustaining flame propagation

(for a comprehensive and clarity oriented study of Zones see :https://wp.me/s8t0O-zones )

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ZONE 2

That area in which an  Explosive Gas Atmosphere , consisting of a mixture with air of Flammable substance in the form of gas, vapor or mist is not likely to occur in normal operation but, if it does occur , will persist for a short period only. In view of this official definition the Equipment Protection Level (EPL) exclisively used is Gc.

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)

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DOMAIN of Ex n 

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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)

 

 

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

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The new nC (Modified ) domain 

 

The simple meaning of the above diagram is as follows :

Equipment or components which in normal operation produce arcs, sparks or hot surfaces which otherwise would be capable of igniting a surrounding atmosphere shall be protected against causing ignition by one or more of the following methods, all of which provide Equipment Protection Level Gc:

• 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.

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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

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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.

Alternately : Device which is so constructed that it cannot be opened and is sealed effectively by fusion
to prevent entry of an external atmosphere

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.

Alternately : Component having contacts for making or breaking a specified ignition capable circuit but in which the contacting mechanism is designed and constructed so that the component is not capable of causing ignition of the specified explosive gas atmosphere

nR  (Restricted breathing 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

Alternately :Enclosure that is designed to restrict the entry of gases, vapours and mists

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

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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 ec 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

ec(nA previous marking ): non-Sparking Equipment

d   : flame-proof component

IIB : Gas Group

Gc : EPL

12345FG X: X indicates the special conditions of use

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2. Ex nR IIC Gc

Certificate No: 7865 U

Its a restricted breathing enclosure as a component

 

History of Ex n

Traditionally   Ex n  consisted of  following  EPLs  :-

 

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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 

 

……..Existing ZONE 2 Protection Basket

 

 

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