Page 615 - Wago_Rail-MountedTerminalBlockSystems_Volume1_2015_US.pdf

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EN 60079-0 also classified electrical This information is also given under Item Thermal resistance of the insulating mate-
equipment for use in hazardous areas 12 in the EC Prototype Test Certificates, rial must be at least 20°C greater than
into two groups: based on which the terminal blocks have the highest operating temperature. Low
been approved for Group I and Group temperature stability is considered to be
Group I: II. sufficient when the insulating material can
Electrical equipment for mines susceptible withstand 24-hour storage at a tempera-
Maximum
to firedamp. Temperature Surface Temperature °C ture of -60°C without nullifying the type
Category
T1 450 of protection.
Group II: T2 300
Electrical equipment for potentially explo- T3 200 Special Requirements
sive areas, except for mines susceptible T4 135 “Increased Safety Ex e”
to firedamp. T5 100 The European Standard EN 60079-7 –
As this broad application range encom- T6 85 VDE 0170, Part 6 – contains “special
passes a large number of potentially requirements” for the design and testing
flammable gases, Group II is broken Depending on the maximum surface tem- of electrical equipment with protection
down into subgroups IIA, IIB and IIC. perature, electrical equipment in Group II type – Increased safety “e” – for use in
This breakdown is based on different gas- are classified in temperature categories hazardous areas.
es/materials exhibiting differing ignition T1 to T6 protection types. The ambient This standard is a supplement to EN
power levels as parameters. Therefore, temperature, which must be accounted 60079-0 and applies to equipment or
representative gases have been allocated for in dimensioning, is defined as 40°C parts thereof that neither generate sparks
to these three sub-groups: (104°F) (deviations are acceptable or arcing under normal operating condi-
● IIA – Propane under some conditions). tions, nor exhibit hazardous temperatures.
● IIB – Ethylene This standard describes special measures,
● IIC – Hydrogen Terminal blocks protection type – which have to be observed to obtain a
Increased safety “e” – are generally safety degree according to the type of
Publication of the WBK Mining Author- assigned to temperature category T6. protection – Increased safety “e” –.
ity dated March 1989. When terminal blocks are used in equip- Ex components such as rail-mounted ter-
Quote: “ . . . terminal blocks that have ment of temperature categories T1 to T5, minal blocks are covered by Section 4.2
been certified for the type of protection ensure that the highest temperature on “Terminal Blocks for External Conduc-
Ex e II will also be accepted, for exam- the insulating parts does not exceed tors.”
ple, for Group I – Electrical equipment 85°C (185°F). The following are the most important
of the type of protection – Increased The highest measured surface tempera- design requirements for terminal blocks
safety “e”. ture rise shall not exceed 40 K. for external electrical conductors:
These must:
● be sufficiently large to permit reliable
Minimum Ignition Power of Typical Gases: connection of external conductors
with cross section of at least the size

Explosion Group I IIA IIB IIC required by the nominal current of the
equipment.
Gases Methane Propane Ethylene Hydrogen ● be protected against self-loosening
and designed such that the external
Ignition Power 280 250 82 16
conductors cannot slip out of their
clamping units.
The following table shows a comparison between the current practice based ● be designed such that adequate con-
on ElexV, DIN VDE 0165: 1991 and the new EN 1127-1: tact pressure is ensured without dam-
Device Group II aging the conductors.
Category Protection Adequate safety Comparable to New, ● be designed such that their contact
degree for current practice based on pressure does not change with tem-
EN 1127 perature cycling.
● be equipped with a spring connect-
1 Ex atmosphere Highest 2 protective Group II Zone 0
is very probable, measures Zone 0 Zone 20 ing link for the connection of stranded
dust in air 2 faults Zone 10 conductors. 14
2 Occasional Increased Equipment Group II Zone 1 ● be designed so as to allow safe con-
Ex atmosphere failure or Zone 1 Zone 21 nection of smaller conductor cross sec-
fault tions for terminal blocks up to 4 mm² /
3 Low probability of Normal Fault-free Group II Zone 2 AWG 12.
Ex atmosphere, operation Zone 2 Zone 22
settled dust Zone 11