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IECEx scheme<br />
IECEx scheme<br />
Technical appendix<br />
The IECEx scheme is an international certification<br />
scheme for products which meet the requirements of the<br />
international standards, e.g. the technical committee TC31’s<br />
IEC standards.<br />
The certificates awarded in this scheme are published on the<br />
IECEx website (www.iecex.com) as an electronic certificate.<br />
They can be viewed online and printed out.<br />
A Certificate of Conformity (CoC) refers to a test report<br />
(Ex Test Report ExTR) and on an assessment of the quality<br />
assessment report from the manufacturer (QAR).<br />
The standards used for the production of the test report<br />
correspond almost entirely to the harmonised standards<br />
in Europe. Recent EN standards were initially adopted as<br />
IEC standards.<br />
Protection concepts<br />
The zoning described above provides the basis for the<br />
selection of the type of ignition protection. So, as an<br />
example, in the ATEX applicable areas, only ignition<br />
protection devices meeting Ex ia for Zone 0 (highest<br />
probability of an explosive atmosphere being present) are<br />
allowed.<br />
Increased safety Ex e<br />
No sparks and a surface temperature limited<br />
to a safe level<br />
Increased safety is for products where there<br />
are no sparks produced during normal<br />
operation or in case of a failure. The surface<br />
temperature of the relevant parts is limited<br />
to a value below the ignition temperature.<br />
Increased safety is achieved by reducing the current load<br />
and raising the isolation properties and by maintaining<br />
clearance and creepage distances above the value in an<br />
industrial application. The highest voltage permitted for this<br />
protection scheme is 11 kV (D.C. or A.C. rms).<br />
This protection scheme is usually used for distribution<br />
cabinets..<br />
Intrinsically safe Ex i<br />
Limited to a safe level of ignition energy<br />
Intrinsic safety is for products where<br />
electrical energy which flows into the<br />
product, or is stored in the product, is not<br />
sufficient to ignite the surrounding explosive<br />
atmosphere. This also applies in fault<br />
conditions. The methods that achieve intrinsic safety mean<br />
that it is important that not only the devices installed in<br />
direct contact with the explosive atmosphere are<br />
constructed correctly, but also the electrical devices to<br />
which they are connected.<br />
Intrinsically safe equipment and intrinsically safe parts of the<br />
associated equipment are divided into protection levels: ia<br />
(for zones 0, 1, and 2), ib (for zones 1 and 2), and ic (only for<br />
zone 2).<br />
A typical application area are control and display circuits<br />
with low voltage and current.<br />
Pressure-resistant Ex d encapsulation<br />
Limits the explosion to the inside of the enclosure<br />
Pressure-resistant encapsulated enclosures<br />
are designed for devices where sparks are<br />
generated or which have hot surfaces which<br />
are a source of ignition during normal<br />
operation. Similarly, industrial components<br />
for use in potentially explosive atmospheres are often made<br />
suitable by encapsulating them in a pressure-resistant<br />
enclosure which otherwise could not be used.<br />
The surrounding possibly explosive atmosphere can enter<br />
the enclosure and will produce an internal explosion during<br />
the equipment’s lifespan.<br />
The enclosure must therefore be stable enough to ensure<br />
that it is not deformed or destroyed by the pressure created.<br />
All connections of the enclosure are sized so that they<br />
cannot transmit an explosion from inside to the surrounding<br />
atmosphere. These connections are known as ignition gaps.<br />
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