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Application in Explosive Environments • 307

8.3.3Unit 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
categories	group
categories	group
M1	I	Fire-damp protection

M2	I	Fire-damp protection

1G	II	Zone 0 Explosive environment by gas, fumes or mist

2G	II	Zone 1 Explosive environment by gas, fumes or mist

3G	II	Zone 2 Explosive environment by gas, fumes or mist

1D	II	Zone 20 Explosive environment by dust

2D	II	Zone 21 Explosive environment by dust

3D	II	Zone 22 Explosive environment by dust

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308 • Application in Explosive Environments

8.3.4Temperature 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
	temperature	of the combustible materials
	temperature	of the combustible materials

T1	450 °C	> 450	°C

T2	300 °C	> 300	°C - 450 °C

T3	200 °C	> 200	°C - 300 °C

T4	135 °C	> 135	°C - 200 °C

T5	100 °C	>100 °C -135 °C

T6	85°C	> 85	°C - 100 °C

The following table represents the division and attribution of the materials to the temperature classes and material groups in percent:

Temperature classes

T1	T2	T3	T4		T5	T6	Total*
26.6 %	42.8 %	25.5 %

	94.9 %		4.9 %		0 %	0.2 %	432

Explosion group

IIA	IIB	IIC					Total*
80.2 %	18.1 %	0.7 %					436
				* Number of classified materials

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Application in Explosive Environments • 309

8.3.5Types 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:

Identifi-	CENELEC stan-	IEC stan-	Explanation	Application
cation	dard	dard
cation	dard	dard

EEx o	EN 50 015	IEC 79-6	Oil encapsulation	Zone 1 + 2

EEx p	EN 50 016	IEC 79-2	Overpressure encap-	Zone 1 + 2
			sulation

EEx q	EN 50 017	IEC 79-5	Sand encapsulation	Zone 1 + 2

EEx d	EN 50 018	IEC 79-1	Pressure resistant	Zone 1 + 2
			encapsulation

EEx e	EN 50 019	IEC 79-7	Increased safety	Zone 1	+ 2

EEx m	EN 50 028	IEC 79-18	Cast encapsulation	Zone 1	+ 2

EEx i	EN 50 020 (unit)	IEC 79-11	Intrinsic safety	Zone 0	+ 1 + 2
	EN 50 039 (system)

EEx n	EN 50 021	IEC 79-15	Electrical components	Zone 2
			for zone 2 (see below)

Ignition protection “n“ describes exclusively the use of explosion protected electrical components in zone 2. This zone encompasses 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)

•AC – spark generating, contacts protected by seals (function modules with relays / without switches)

•L – limited energy (function modules with switch)

Further information

i For more detailed information please refer to the national and/or international standards, directives and regulations!

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8.4 Classifications meeting the NEC 500

The following classifications according to NEC 500 (National Electric Code) are valid for North America.

8.4.1Divisions

The "Divisions" describe the degree of probability of whatever type of dangerous situation occurring. Here the following assignments apply:

Explosion endangered areas due to combustible gases, fumes, mist and dust:

Division 1

Division 2

encompasses areas in which explosive atmospheres are to be expected occasionally (> 10 h ≤ 1000 h /year) as well as continuously and long-term (> 1000 h /year).

encompasses areas in which explosive atmospheres can be expected rarely and short-term (>0 h ≤ 10 h /year).

8.4.2Explosion protection groups

Electrical components for explosion endangered areas are subdivided in three danger categories:

Class I (gases and fumes):

Class II (dust):

Class III (fibers):

Group A (Acetylene)

Group B (Hydrogen)

Group C (Ethylene)

Group D (Methane)

Group E (Metal dust) Group F (Coal dust)

Group G (Flour, starch and cereal dust)

No sub-groups

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Application in Explosive Environments • 311

8.4.3Temperature classes

Electrical components for explosive areas are differentiated by temperature classes:

Temperature classes	Maximum	Ignition temperature
	surface temperature	of the combustible materials
	surface temperature	of the combustible materials

T1	450 °C	> 450 °C

T2	300 °C	> 300 °C - 450 °C

T2A	280 °C	> 280 °C - 300 °C

T2B	260 °C	> 260 °C - 280 °C

T2C	230 °C	>230 °C - 260 °C

T2D	215 °C	>215 °C - 230 °C

T3	200 °C	>200 °C - 215 °C

T3A	180 °C	>180 °C - 200 °C

T3B	165 °C	>165 °C - 180 °C

T3C	160 °C	>160 °C - 165 °C

T4	135 °C	>135 °C - 160 °C

T4A	120 °C	>120 °C - 135 °C

T5	100 °C	>100 °C - 120 °C

T6	85 °C	> 85 °C - 100 °C

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