Hazardous Areas – IEC and NEC/CEC Comparison

By Steven McFadyen on March 9th, 2012

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	Intended to prevent a potential ignition arising
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 15^o)	0.375 Joule
3	Objects > 2.5 mm dia.	Spraying water (up to 60^o)	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.

Hazardous Areas, Standards, Safety

More interesting Notes:

Possibly related posts:

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