Hazardous Areas – IEC and NEC/CEC Comparison 

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SasolSA
Sasol, South Africa

Depending on where in the world you work, you are likely following one of two standards

  • International Electrotechnical Commission (IEC)
  • National Electrical Code/Canadian Electrical Code (NEC/CEC)

The different nature of the two systems makes a direct comparison almost impossible.

If you do need to work with both systems or transition from one to the other, hopefully, the following will make this easier.

Since July 2003, Ex products in Europe must also be certified to the ATEX directive (ATEX 94/9/EC).

Zones & Divisions

 IEC Classification IEC 60079    ANSI/NFPA 70 NEC Article 500
Gas and Vapours
Zone 0 flammable atmosphere highly likely to be present - may be present for long periods or even continuously
Zone 1 flammable atmosphere possible but unlikely to be present for long periods
Zone 2 flammable atmosphere unlikely to be present except for short periods of time - typically as a result of a process fault condition
Dusts
Zone 20 dust cloud likely to be present continuously or for long periods
Zone 21 dust cloud likely to be present occasionally in normal operation
Zone 22 dust cloud unlikely to occur in normal operation, but if it does, will only exist for a short period
 
Class (nature of the material)
Class I hazardous because flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures
Class II hazardous because combustible or conductive dusts are present
Class III hazardous because ignitable fibers or flying's are present, but not likely to be in suspension in sufficient quantities to produce ignitable mixtures.
Division (probability of material being present)
Division 1 the substance referred to by class is present during normal conditions
Division 2 the substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown

Temperature & Explosion Groups

 Explosion Groups    Temperature Class
  IEC NEC/CEC
Inflammable material Zone Group Class Division Group
Gas and Vapours
Acetylene 0,1 or 2 II C I 1 or 2 A
Hydrogen 0,1 or 2 II B+H2 I 1 or 2 B
Propylene oxide
Ethyl oxide
Butadiene
0,1 or 2 II B I 1 or 2 B
Cyclopropane
Ethly ether
Ethylene
0,1 or 2 II B I 1 or 2 C
Acetone
Benzene
Butane
Hexane
Paint solvents
Natural gas
0,1 or 2 II A I 1 or 2 D
Dusts
Metal dust   III C II   E
Coal dust   III C II   F
Grain dust   III B II   G
Wood
Paper
Cotton
  III A III    
 
Temperature
oC
IEC NEC/CEC
85 T6 T6
100 T5 T5
120
135
T4
T4
T4A
T4
160
165
180
200
T3
T3
T3
T3
T3C
T3B
T3A
T3
215
230
260
280
300
T2
T2
T2
T2
T2
T2D
T2C
T2B
T2A
T2
450 T1 T1
                  

Gas Group / Temperature Class
Group T1 T2 T3 T4 T5 T6
I Methane          
IIA

Acetone
Methane
Ethane
Benzene
Methanol
Toluene

Propane
Acetic Acid
Ammonia

Ethanol
Cyclohexane
Propanol 2
N-Butyl alcohol
N-butane
Diesel fuel
Aircraft fuel
Fuel oil
N-Hexane
Heptane
Kerosene
Acetaldehyde
   
IIB Coal Gas Ethylene
Ethylene oxide
Propanol 1
Methyl Ethyl
Ketone
Ethylene glycol
Hydrogen Sulphide
Tetrahydrofuran
Ethyl Methyl Ether
   
IIC Hydrogen Acetylene        
       
 
Ignition Temperatures for Common Flammable Dusts and Fibers
  Ignition Temperature
Material Cloud Layer
Coal Dust 380°C 225°C
Polythene 420°C (melts)
Methyl Cellulose 420°C 320°C
Starch 460°C 435°C
Flour 490°C 340°C
Sugar 490°C 460°C
Grain Dust 510°C 300°C
Phenolic Resin 530°C > 450°C
Aluminium 590°C > 450°C
PVC 700°C > 450°C
Soot 810°C 570°C
       

Equipment & Protection Levels

IEC/ATEX Equipment Protection
Level (EPL)
   IEC Equipment Classification
IEC 60079 94/9/EC (ATEX)

EPL

Zone(s)

Group

Category
Protection
Level
Gas/Vapours
Ga 0,1,2 II 1 G very high
Gb 1,2 II 2 G high
Gc 2 II 3 G increased
Dusts
Da 20,21,22 III 1 D very high
Db 21,22 III 2 D high
Dc 22 III 3 D increased
Methane, Coal Dust
Ma Mining I M1 very high
Mb Mining I M2 high

 

NEC/CEC Equipment Classification

Method of Protection Division
Intrinsic Safety, IS 1 or 2
Explosion-Proof, XP 1 or 2
Pressurization, X,Y,Z 1 or 2
Non-incendive equipment 2

Specifically assessed equipment

2
 
Code Description EPL Type of Protection
Ex e Increased safety Gc Intended to prevent a potential ignition arising
Ex n Type - n protection Gc
Ex ia Intrinsic safety 'ia' Ga Intended to limit the ignition energy of the equipment
Ex ib Intrinsic safety 'ib' Gb
Ex ic Intrinsic Safety 'ic' Gc
Ex n Type - n protection Gc
Ex p Purge/pressurized protection Gb Intended to prevent the explosive atmosphere contacting the ignition
source
Ex px Purge/pressurized protection 'px' Gb
Ex py Purge/pressurized protection 'py' Gb
Ex pz Purge/pressurized protection 'pz' Gc
Ex m Encapsulation Gb
Ex ma Encapsulation Ga
Ex mb Encapsulation Gb
Ex o Oil immersion Gb
Ex n Type - n protection Gc
Ex d Flameproof protection Gb Intended to prevent an ignition from escaping outside the equipment
Ex q Sand / powder (quartz) filling Gb
Ex nC Type - n protection Gc
Ex s Special protection Refer to equipment marking and documentation

Degrees of Protection

Ingress Protection Codes
IPxx (IEC 60079)
   NEMA Enclosure Types (& IEC IP Equivalent)
x 1st Numeral
Solid Bodies
2nd Numeral
Liquids
3rd (optional)
Impact
0 No protection No protection No protection
1 Objects > 50 mm dia. Vertically dripping water 0.225 Joule
2 Objects > 12.5 mm dia. Angled dripping water (up to 15o) 0.375 Joule
3 Objects > 2.5 mm dia. Spraying water (up to 60o) 0.5 Joule
4 Objects > 1.0 mm dia. Splashing water (all directions) 2.0 Joule
5 Dust protected Low pressure water jets 6.0 Joule
6 Dust tight High pressure water jets 20.0 Joule
7   Temporary immersion  
8   Continuous immersion  
 
Type Area Description IP
1 Indoor General Purpose 10
2 Indoor Drip proof protection against falling water and dirt 11
3 Indoor
Outdoor
Dust & rain tight protection against windblown dust, rain, and sleet & damage from formation of ice 54
3R Outdoor Rain proof & ice/sleet proof protection against falling rain & damage from formation of ice 14
3S Outdoor Dust tight, rain tight, & ice/sleet proof protection against sleet and damage from formation of ice 55
4 Indoor
Outdoor
Water tight & dust tight 66
4X Indoor
Outdoor
Water tight, dust tight, & corrosion resistant protection from corrosion, hose directed water and damage from formation of ice 66
5 Indoor Dust tight & drip tight protection against dust, fibres, falling dirt, and dripping non-corrosive liquids 52
6 Indoor
Outdoor
Temporary submersion protection against falling dirt, dust, fibres, hose directed water and temporary submersion in water 67
6P Indoor
Outdoor
Prolonged submersion protection against falling dirt, dust, fibres, hose directed water and prolonged submersion in water 67
7 Indoor Class I, Division 1, Groups A, B, C, and D hazardous locations, air-break equipment  
8 Indoor
Outdoor
Class I, Division 1 Groups A, B, C, and D hazardous locations, oil-immersed equipment  
9 Indoor Class II, Division 1, Groups E, F, and G hazardous locations, air-break equipment  
10 Mining Mining applications  
12 Indoor Dust tight & drip tight protection against dust, fibres, falling dirt, and dripping non-corrosive liquids (enclosure without knockouts) 52
12K Indoor Dust tight & drip tight protection against dust, fibres, falling dirt, and dripping non-corrosive liquids (enclosure with knockouts) 52
13 Indoor Dust tight & oil tight protection against dust, spraying of water, oil, and noncorrosive coolant. 54

Product Markings

Typical IEC Type Marking

Typical NEC/CEC Type Marking

As a general rule equipment should be marked as follows:

  • Company/Manufacturers name
  • Class I, II and/or III
  • Division 1 and/or 2
  • Group A, B, C, D, E, F and/or G
  • Approving NRTL (Nationally Recognized Testing Laboratory) logo
  • Product identification
  • Serial number
  • Other relevant safety information
  • Enclosure Type Rating

Finally

Finally the end...  When I started this post I thought it would be one of the easier ones - reproduce and sort a few tables and I'm done.  Well, it took a lot longer than I had anticipated and quite a bit more work.  Anyhow now that it's finished I relieved. Having said that, if anyone notices any errors or has suggestions to improve the post, please add them below and I'll update the post as necessary.



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

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