Материал: m083300e
Explosive Environments • 137
Classification meeting CENELEC / IEC
Explosive areas resulting from combustible gases, fumes or mist:
•Zone 0 areas are subject to an explosive atmosphere (> 1000 h /year) continuously or for extended periods.
•Zone 1 areas can expect the occasional occurrence of an explosive atmosphere (> 10 h ≤ 1000 h /year).
•Zone 2 areas can expect the rare or short-term occurrence of an explosive atmosphere (> 0 h ≤ 10 h /year).
Explosive areas subject to air-borne dust:
•Zone 20 areas are subject to an explosive atmosphere (> 1000 h /year) continuously or for extended periods.
•Zone 21 areas can expect the occasional occurrence of an explosive atmosphere (> 10 h ≤ 1000 h /year).
•Zone 22 areas can expect the rare or short-term occurrence of an explosive atmosphere (> 0 h ≤ 10 h /year).
7.3.2Explosion protection group
In addition, the electrical components for explosive areas are subdivided into two groups:
Group I: Group I includes electrical components for use in fire-damp mine structures.
Group II: Group II includes electrical components for use in all other explosive environments. The group is further subdivided by pertinent combustible gasesin the environment.
Subdivision IIA, IIB and IIC takes into account that different materials/substances/gases have various ignition energy characteristic values. For this reason the three sub-groups are assigned representative types of gases:
•IIA – Propane
•IIB – Ethylene
•IIC – Hydrogen
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Minimal ignition energy of representative types of gases |
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Explosion group |
I |
IIA |
IIB |
IIC |
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Gases |
Methane |
Propane |
Ethylene |
Hydrogen |
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Ignition energy (mWs) |
0,28 |
0,25 |
0,082 |
0,016 |
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WAGO-I/O-SYSTEM 750 |
D R A F T |
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PROFIBUS |
2001-02-27 |
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138 • Explosive Environments
Classification meeting CENELEC / IEC
7.3.3Unit categories
Moreover, the areas of use (zones) and the conditions of use (explosion groups) are subdivided into categories for the electrical operating means:
Unit |
Explosion |
Area of use |
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categories |
group |
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M1 |
I |
Fire-damp protection |
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M2 |
I |
Fire-damp protection |
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1G |
II |
Zone 0 |
Explosivi environment by gas, fumes or mist |
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2G |
II |
Zone 1 |
Explosive environment by gas, fumes or mist |
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3G |
II |
Zone 2 |
Explosive environment by gas, fumes or mist |
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1D |
II |
Zone 20 Explosive environment by dust |
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2D |
II |
Zone 21 Explosive environment by dust |
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3D |
II |
Zone 22 Explosive environment by dust |
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D R A F T |
WAGO-I/O-SYSTEM 750 |
2001-02-27 |
PROFIBUS |
Explosive Environments • 139
Classification meeting CENELEC / IEC
7.3.4Temperature classes
The maximum surface temperature for electrical components of explosion protection group I is 150 °C (danger due to coal dust deposits) or 450 °C (if there is no danger of coal dust deposit).
In line with the maximum surface temperature for all ignition protection types, the electrical components are subdivided into temperature classes, as far as electrical components of explosion protection group II are concerned. Here the temperatures refer to a surrounding temperature of 40 °C for operation and testing of the electrical components. The lowest ignition temperature of the existing explosive atmosphere must be higher than the maximum surface temperature.
Temperature classes |
Maximum surface |
Ignition temperature |
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temperature |
of the combustible materials |
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T1 |
450 °C |
> 450 |
°C |
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T2 |
300 °C |
> 300 |
°C ≤ 450 °C |
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T3 |
200 °C |
> 200 |
°C ≤ 300 °C |
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T4 |
135 °C |
> 135 |
°C ≤ 200 °C |
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T5 |
100 °C |
>100 °C ≤ 135 °C |
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T6 |
85°C |
> 85 |
°C ≤ 100 °C |
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The following table represents the division and attribution of the materials to the temperature classes and material groups in percent:
Temperature classes
T1 |
T2 |
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T3 |
T4 |
T5 |
T6 |
Total |
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28 % |
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37,6 % |
30.5 % |
3,1 % |
0 % |
0,3 % |
351 |
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96,5 % |
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Explosion group |
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IIA |
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IIB |
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IIC |
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Total |
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80,2 % |
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18,1 % |
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0,7 % |
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436 |
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7.3.5Types of ignition protection
Ignition protection defines the special measures to be taken for electrical components in order to prevent the ignition of surrounding explosive atmospheres. For this reason a differentiation is made between the following types of ignition protection:
WAGO-I/O-SYSTEM 750 |
D R A F T |
PROFIBUS |
2001-02-27 |
140 • Explosive Environments
Classification meeting CENELEC / IEC
Identification |
CENELEC stan- |
Explanation |
Application |
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dard |
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EEx o |
EN 50 015 |
Oil encapsulation |
Zone 1 + 2 |
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EEx p |
EN 50 016 |
Overpressure encapsulation |
Zone 1 + 2 |
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EEx q |
EN 50 017 |
Sand encapsulation |
Zone 1 + 2 |
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EEx d |
EN 50 018 |
Pressure resistant encapsu- |
Zone 1 + 2 |
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lation |
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EEx e |
EN 50 019 |
Increased safety |
Zone 1 + 2 |
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EEx m |
EN 50 028 |
Cast encapsulation |
Zone 1 + 2 |
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EEx i |
EN 50 020 (Unit) |
Intrinsic safety |
Zone 0 + 1 + 2 |
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EN 50 039 (System) |
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EEx n |
EN 50 021 |
Components for zone 2 |
Zone 2 |
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(see below) |
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Ignition protection “n“ describes exclusively the use of explosion protected components in zone 2. This zone encompasses three areas where explosive atmospheres can only be expected to occur rarely or short-term. It represents the transition between the area of zone 1, which requires an explosion protection and safe area in which for instance welding is allowed at any time.
Regulations covering these electrical components are being prepared on a world-wide scale. The standard EN 50 021 allows electrical component manufacturers to obtain certificates from the corresponding authorities for instance KEMA in the Netherlands or the PTB in Germany, certifying that the tested components meet the above mentioned standards draft.
Type “n” ignition protection additionally requires electrical components to be marked , with the following extended identification:
•A – non spark generating (function modules without relay /without switches), previously V
•AC – spark generating, contacts protected by seals (function modules with relays / without switches), previously VW
•L – limited energy (function modules with switch)
More information
i For more detailed information please refer to the national and/or international standards, directives and regulations!
D R A F T |
WAGO-I/O-SYSTEM 750 |
2001-02-27 |
PROFIBUS |
Explosive Environments • 141
Classifications meeting the NEC
7.4 Classifications meeting the NEC
The following classifications according to NEC 500 (National Electric Code) are valid for North America, in contrast to the specifications governing use in Europe:
7.4.1Division into zones
An indication for the probability of a danger – of whatever type it may be – is subdivided into “Divisions“. Here are the following descriptions:
Explosion endangered areas due to combustible gases, fumes, mist and dust:
Division 1 encompasses areas in which explosive atmospheres are to be expected occasionally (> 10 h ≤ 1000 h /year) as well as continuously and longterm (> 1000 h /year).
Division 2 encompasses areas in which explosive atmospheres can be expected rarely and short-term (>0 h ≤ 10 h /year).
7.4.2Explosion protection groups
Electrical components for explosion endangered areas are subdivided in three danger categories:
Class I (gases and fumes): |
Group A (Acetylene) |
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Group B (Hydrogen) |
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Group C (Ethylene) |
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Group D (Methane) |
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Class II (dust): |
Group E (Metal dust) |
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Group F (Coal dust) |
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Group G (Flour, starch and cereal dust) |
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Class III (fibers): |
No sub-groups |
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WAGO-I/O-SYSTEM 750 |
D R A F T |
PROFIBUS |
2001-02-27 |