GB/T 3836.18-2024 Explosive atmospheres — Part 18: Intrinsically safe electrical systems
1 Scope
This document specifies the specific requirements for design, construction and assessment of intrinsically safe systems (Type of Protection “i”).
This document is applicable to the intrinsically safe systems intended for use, as a whole or in part, in locations in which the use of Group I, II or III Ex Equipment is required.
Note 1: This document is intended for use by the designer of the system e.g. a person who could be a manufacturer, a third party, a specialist consultant or a member of the end-user’s staff.
This document supplements and modifies the general requirements of GB/T 3836.1 and the intrinsic safety standard GB/T 3836.4. Where a requirement of this document conflicts with a requirement of GB/T 3836.1 or GB/T 3836.4, the requirement of this document takes precedence.
The installation requirements of Group II or Group III systems designed in accordance with this document are specified in GB/T 3836.15.
Note 2: Group I installation requirements are presently not provided in GB/T 3836.15. Installation requirements for Group I are being considered.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 3836.1 Explosive atmospheres - Part 1: Equipment - General requirements (GB 3836.1-2021, IEC 60079-0:2017, MOD)
GB/T 3836.4 Explosive atmospheres - Part 4: Equipment protection by intrinsic safety "i” (GB/T 3836.4-2021, IEC 60079-11:2011, MOD)
GB/T 3836.15 Explosive atmospheres - Part 15: Electrical installations design, selection and erection (GB/T 3836.15-2017, IEC 60079-14:2007, MOD)
GB/T 16657.2 Industrial communication networks - Fieldbus specifications - Part 2: Physical layer specification and service definition (GB/T 16657.2-2008, IEC 61158-2:2007, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 4960.1 and GB/T 3836.4 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC: http://www.electropedia.org/;
— ISO: http://www.iso.org/obp.
3.1
intrinsically safe system
assembly of interconnected items of apparatus, described in a descriptive system document, in which the circuits or parts of circuits, intended to be used in an explosive atmosphere, are intrinsically safe circuits
3.2
multi-circuit cable
multi-core cable containing more than one intrinsically safe circuit
3.3
descriptive system document
document in which the items of apparatus, their intrinsic safety parameters and those of the interconnecting wiring are specified
3.4
total cable capacitance
Cc
total capacitance of the interconnecting cable that can be connected into an intrinsically safe circuit
3.5
total cable inductance
Lc
total inductance of the interconnecting cable that can be connected into an intrinsically safe circuit
3.6
cable inductance to resistance ratio
Lc/Rc
value of the ratio inductance (Lc) to resistance (Rc) of the interconnecting cable connected into an intrinsically safe circuit
3.7
linear power source
power source from which the available output current is determined by a resistor; the output voltage decreasing linearly as the output current increases
3.8
non-linear power source
power source where the output voltage and output current have a non-linear relationship
Note: For example, a supply with a constant voltage output that can reach a constant current limit controlled by semiconductors
3.9
fieldbus intrinsically safe concept; FISCO
intrinsically safe system architecture that is bus-powered and designed in accordance with specific requirements
Note: The requirements are specified in GB/T 16657.2.
4 Descriptive system document
A descriptive system document shall be created for all intrinsically safe systems. The descriptive 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 including simple apparatus and the interconnecting wiring;
b) a statement of the equipment Group subdivision (for equipment Groups II and III), the Level of Protection and the Equipment Protection Level (EPL) for each part of the system, the temperature 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 with GB/T 3836.4;
f) the result of the assessment of intrinsically safe systems in accordance with Clause 12;
g) a unique document identification.
The requirements found in Clauses 5 through 12 shall be used to determine the content of the descriptive system document.
Note: The descriptive system document is not the same as the control drawing referred to in GB/T 3836.4.
Annex A shows an example of a typical diagram, illustrating the requirements of the descriptive system document.
5 Grouping and temperature classification
Parts of intrinsically safe systems that are intended for use in an explosive atmosphere shall be grouped in accordance with the equipment grouping requirements of .GB/T 3836.1 and be assigned a temperature class or a maximum surface temperature in accordance with the temperature requirements of .GB/T 3836.1 and GB/T 3836.4.
Associated apparatus not intended for use in an explosive atmosphere shall only be grouped in accordance with the equipment grouping requirements of GB/T 3836.1.
Where the intrinsically safe system or parts of the intrinsically safe system are specified as being suitable for operation outside the normal ambient temperature range of -20°C and +40°C, 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 have different temperature classes and different ambient temperature ratings.
6 Level of Protection
6.1 General
Each part of an intrinsically safe system intended for use in an explosive atmosphere shall have a Level of Protection “ia”, “ib” or “ic” in accordance with GB/T 3836.4 and an EPL in accordance with GB/T 3836.1. Separate parts of the system may have a different Level of Protection or EPL.
Note: For Group I applications, an intrinsically safe system can be “ib” in normal operation with external power, but when power is removed under defined safety circumstances (e.g. ventilation failure) then the system could become “ia” under back up battery power. The Level of Protection will be clearly defined for intended circumstances.
6.2 Level of Protection “ia”
Where the requirements applicable to apparatus of Level of Protection “ia” (see GB/T 3836.4) are satisfied by an intrinsically safe system or part of a system considered as an entity, then that system or part of a system shall be assigned a Level of Protection “ia”.
6.3 Level of Protection “ib”
Where the requirements applicable to apparatus of Level of Protection “ib” (see GB/T 3836.4) are satisfied by an intrinsically safe system or part of a system considered as an entity, then that system or part of a system shall be assigned a Level of Protection “ib”.
Example: A Level of Protection “ia” field instrument powered via a Level of Protection “ib” associated apparatus would be considered as a Level of Protection “ib” system or a Level of Protection “ib” field instrument powered via a Level 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 GB/T 3836.4) are satisfied by an intrinsically safe system or part of a system considered as an entity, then that system or part of a system shall be assigned a Level of Protection “ic”.
Foreword II Introduction VII 1 Scope 2 Normative references 3 Terms and definitions 4 Descriptive system document 5 Grouping and temperature classification 6 Level of Protection 7 Non-intrinsically safe circuits 8 Interconnecting wiring/cables used in an intrinsically safe system 9 Requirements of single and multi-circuit cables 10 Enclosures 11 Earthing and bonding of intrinsically safe systems 12 Assessment of an intrinsically safe system 13 Predefined systems Annex A (Informative) Example format for a descriptive system document Annex B (Normative) FISCO systems Annex C (Informative) Use of simple apparatus in systems Annex D (Informative) Assessment of a simple intrinsically safe system Annex E (Informative) Assessment of circuits with more than one power source Annex F (Informative) Interconnection of non-linear and linear intrinsically safe circuits Annex G (Normative) Verification of inductive parameters
