IEC 60079-25-2020 pdf free download – Explosive atmospheres – Part 25: Intrinsically safe electrical systems.
4Descriptive system document
A descriptive system documentshall be created for all intrinsically safe systems. Thedescriptive system document shall include the technical justification for the combination of the
apparatus and shall include at a minimum the following:
a) a block diagram of the system listing all the items of apparatus within the system includingsimple apparatus and the interconnecting wiring;
b) a statement of the equipment Group subdivision (for equipment Groups ll and llI), the Level of Protection and the Equipment Protection Level’(EPL) for each part of the system,thetemperature classification, and the ambient temperature rating in accordance with Clauses 5 and 6;
c) the requirements and permitted parameters of the interconnecting wiring in accordance with Clause 8;
d) details of the earthing and bonding points on which intrinsic safety depends;
e) where applicable，the confirmation of apparatus as simple apparatus in accordance withIEC 60079-11;
f) the result of the assessment of intrinsically safe systems in accordance with Clause 12; andg) a unique document identification.
The requirements found in Clauses 5 through 12 shall be used to determine the content of thedescriptive system document.
NOTE The descriptive system document is not the same as the control drawing referred to in lEC 60079-11.
Annex E shows an example of a typical diagram, illustrating the requirements of the descriptivesystem document.
5 Grouping and temperature classification
Parts of intrinsically safe systems that are intended for use in an explosive atmosphere shallbe grouped in accordance with the equipment grouping requirements of lEC 60079-0 and be assigned a temperature class or a maximum surface temperature in accordance with thetemperature requirements of lEC 60079-0 and lEC 60079-11.
Associated apparatus not intended for use in an explosive atmosphere shall only be grouped inaccordance with the equipment grouping requirements of lEC 60079-0.
Where the intrinsically safe system or parts of the intrinsically safe system are specified asbeing suitable for operation outside the normal ambient temperature range of -20 C and+40C, then this shall be specified in the descriptive system document.
NOTE Different parts of the same intrinsically safe system can have different groups.The apparatus used can havedifferent temperature classes and different ambient temperature ratings.
6Levels of Protection
6.1 General
Each part of an intrinsically safe system intended for use in an explosive atmosphere shall haveaLevel of Protection “ia”, ib” or “ic” in accordance with IEC 60079-11 and an EPL in accordance with IEC 60079-0. Separate parts of the system may have a different Level of Protection orEPL.
6.2Level of Protection “ia”
Where the requirements applicable to apparatus of Level of Protection “ia”(see IEC 60079-11)
are satisfied by an intrinsically safe system or part of a system considered as an entity, thenthat system or part of a system shall be assigned a Level of Protection “ia”.
6.3Level of Protection”ib”
Where the requirements applicable to apparatus of Level of Protection “ib”(see lEC 60079-11)
are satisfied by an intrinsically safe system or part of a system considered as an entity, thenthat system or part of a system shall be assigned a Level of Protection “ib”.
EXAMPLE ALevel of Protection”ia”field instrument powered via aLevel of Protection “ib”associated apparatuswould be considered as a Level of Protection”ib”system or aLevel of Protection”ib”field instrument powered via aLevel of Protection“ia” associated apparatus would also be considered as a Level of Protection “ib”system.
6.4 Level of Protection”ic”
Where the requirements applicable to apparatus of Level of Protection “ic” (see lEC 60079-11)
are satisfied by an intrinsically safe system orpart of a system considered as an entity, thenthat system or part of a system shall be assigned a Level of Protection “ic”.
EXAMPLE ALevel of Protection“ia”field instrument powered via a Level of Protection“ic”associated apparatuswould be considered as Level of Protectionic” system or a Level of Protection“ic” field instrument powered via aLevel of Protection“ia”associated apparatus would also be considered as a Level of Protection “ic”system.
7 Non-intrinsically safe circuits
The descriptive system document shall define the limitations for connection of circuits to thenon-intrinsically safe terminals of associated apparatus,such as the
Um value(s).
8Interconnecting wiring / cables used in an intrinsically safe system
8.1General
The intrinsic safety parameters of the interconnectingwiring upon which intrinsic safetydepends，and their derivation，shall be specified in the descriptive system document. lf aspecific type of wiring is specified,then the justification for its use shall be included in thedocumentation.IEC 60079-25 pdf download.