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This specification was revised by the drafting group according to the requirements of Notice on printing and distributing the development and revision plan on the third batch of professional standards in 2015 (GONGXINTINGKE [2015] No.115) issued by the Ministry of Industry and Information Technology of the People's Republic of China, through extensive investigation, careful summarization of practical experience on specification implementation and actual engineering, reference to relevant international and foreign advanced standards and extensive solicitation of opinions.
This specification comprises 7 clauses and 2 annexes.
The main technical contents of this specification include: function types and earthing method; earthing system configuration; bonding; earthing resistance and bonding resistance.
This specification is a revision of SH/T 3081-2003 Design code for instrument grounding in petrochemical industry, with the main technical contents revised as follows:
——network type earthing configuration is added;
——Annex A (normative) Shielded cable earthing referenced drawing is added;
——Annex B (informative) Network type earthing referenced drawing is added;
China Petrochemical Corporation (SINOPEC) is in charge of the administration of this specification, Automatic Control Design Technology Center Station of China Petrochemical Corporation is responsible for the routine management, and SINOPEC Engineering Incorporation is responsible for the explanation of the specific technical contents. In case of any opinion or suggestion in the process of implementing this specification, please send it to the routine management organization and the chief development organization.
This specification was firstly issued in 1997 and revised for the first time in 2003. This is the second revision.
Design specification for instrumentation earthing in petrochemical engineering
1 Scope
This specification specifies the design principles and technical requirements of earthing types, earthing system configuration, earthing method, engineering implementation, earthing resistance and design scheme of instrumentation system in petrochemical engineering.
This specification is applicable to the engineering design for instrumentation and automatic control system in petrochemical engineering and in new construction, extension and renovation of enterprises using coal as raw materials to prepare oil and chemical products.
2 Normative references
The following documents are indispensable for the application of this specification. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB 50057-2010 Code for design protection of structures against lightning
3 Terms and definitions
For the purposes of this specification, the following terms and definitions apply.
3.1
earthing system
earthing network with bonding wire, bonding conductor, bonding bar, bonding terminal bar, earthing termination system, etc.
3.2
protective earthing
earthing for personal safety and electrical equipment safety, also known as safety earthing
3.3
common bonding
connection between instrumentation signal or DC power supply and common potential reference point
?
3.4
shield earthing
earthing of shielding layer and shielding body to realize electric field shielding and electromagnetic field shielding functions
3.5
electrostatic protective earthing
earthing for discharging static electricity
3.6
lightning protective earthing
earthing for discharging lightning current
3.7
isolative signal
circuit of input signal (or output signal) and circuit of output signal (or input signal) being isolated conductive circuits, both ends of this signal circuit, as well as this signal circuit and other circuits being electrically insulated and insulated from the ground
3.8
TN-S system
a form of low-voltage distribution system, with the protection line PE at the power supply being grounded and the protection line PE being separated from the neutral line N in the whole system
3.9
equipotential bonding
electrical connection among various conductive objects such as metal components, metal facilities, metal pipelines and metal equipment with wire or conductor, so that the objects have approximately equal potentials
3.10
common earthing system
earthing system with various earthing facilities, bondings, earthing equipment, equipotential bonding systems and earthing termination systems, which can be used for instrumentation earthing, low-voltage distribution system earthing and lightning protection system earthing
3.11
bonding
connection of the equipment, instrumentation and bonding bar that need to be earthed into an earthing system with bonding wires and conductors
?
3.12
bonding conductor
conductor used for connecting various equipment and bonding bar that need to be earthed into an earthing system
3.13
bonding bar
strip metal with relatively small specifications used for collecting various bonding wires in the cabinet, also known as bonding strip, which may be classified into common bonding bar, protective bonding bar, etc. based on the application
3.14
bonding terminal bar
strip metal terminal bar with large specifications used for collecting multiple bonding wires or bonding trunk wires, which may be classified into common bonding terminal bar, protective bonding terminal bar, main bonding terminal bar, etc. based on the application
3.15
bonding wire
insulated wire for bonding
3.16
bonding trunk wire
insulated wire for connecting various bonding bars
3.17
earthing electrode
buried metal conductor forming electrical contact with the earth, also known as earthing body. Various metal components, metal facilities, metal pipelines, metal equipment, etc., which are in direct contact with the earth, may also be used as earthing electrode, which is called natural earthing electrode
3.18
earthing termination system
set of bonding conductors between earthing electrodes
3.19
bonding resistance
sum of the wire resistance from the earthing terminal of the instrumentation or equipment to the earthing termination system and the contact resistance of the connection point
3.20
earthing resistance
resistance of earthing termination system to ground
3.21
earthing system resistance
sum of bonding resistance and earthing resistance
4 Function types and earthing method
4.1 Protective earthing
4.1.1 The exposed conductive parts of instrumentation and control system shall be provided with protective earthing.
4.1.2 The metal panels, tables, boxes, cabinets and racks equipped with instrumentation or control system should be provided with protective earthing.
4.1.3 The earthed metal panels, tables, boxes, cabinets and racks with good electrical contact, or the exposed conductive parts of instrumentation and control systems which are electrically connected may not be separately provided with protective earthing.
4.1.4 In the non-explosion hazard environment, the metal enclosure, metal protective box and metal junction box of field instrumentation with power supply voltage lower than 36V may not be provided with protective earthing, but those that may contact with equipment with voltage higher than 36V shall be provided with protective earthing.
4.1.5 In explosion hazard environment, the metal enclosure, metal protective box and metal junction box of field instrumentation in non-intrinsic safety system shall be provided with protective earthing, while those in intrinsic safety system may not be provided with protective earthing.
4.1.6 The metal enclosure, metal protective box and metal junction box of field instrumentation used for lightning protection shall be provided with protective earthing.
4.1.7 The metal enclosure, metal protective box and metal junction box of field instrumentation requiring protective earthing shall be connected to the earthing network nearby, or connected to the metal components such as earthed metal cable trough, metal protective pipe, cable armor layer, metal support, frame, platform, fence and equipment.
4.1.8 The metal cable trough and metal protective box shall be provided with protective earthing by being directly welded or connected with bonding wire to the earthing network or metal components such as earthed metal support, frame, platform, fence and equipment; if the cable trough is very long, iterative earthing at multiple points shall be conducted, with the distance between earthing points not greater than 30m.
4.1.9 If the instrumentation, metal protective box and metal junction box in 4.1.4, 4.1.5 and 4.1.6 fail to meet the earthing conditions in 4.1.7, special bonding wire may be laid according to those specified in 6.1.2 b).
4.1.10 Metal cable trough and protective metal pipe shall be connected to the nearby earthing network outside the building before entering the building.
4.2 Common bonding
4.2.1 The instrumentation signal circuit requiring earthing for instrumentation and control systems shall be provided with common bonding.
4.2.2 For non-isolative signal, the negative terminal of DC power supply shall be used as the common terminal as the common bonding reference point.
4.2.3 The isolative signal may not be earthed; the circuits for isolative signals (input or output signals) shall be electrically insulated from the circuits for other signals (input or output signals).
4.2.4 The common bonding shall not be mixed with protective earthing before being connected to the terminal bar or network type bonding bar.
4.2.5 The common bonding wires, connecting points, common bonding strip, etc. shall be insulated from other conductors before being connected to the terminal bar or network type bonding bar.
4.2.6 Single point earthing shall be adopted for the signal circuit.
4.2.7 Multi-point earthing shall be avoided in instrumentation signal circuit. If the signal source and signal receiving terminal on the same wire are inevitably earthed, isolator shall be used to isolate the two earthing points.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Function types and earthing method
4.1 Protective earthing
4.2 Common bonding
4.3 Intrinsic safety system earthing
4.4 Shield earthing
4.5 Electrostatic protective earthing
4.6 Lightning protective earthing
5 Earthing system configuration
5.1 Earthing principle
5.2 Branch type configuration
5.3 Network type configuration
5.4 Combined configuration
6 Bonding
6.1 Bonding wire
6.2 Bonding wire laying
6.3 Bonding bar or terminal bar
6.4 Bonding conductor
7 Earthing resistance and bonding resistance
7.1 Earthing resistance
7.2 Bonding resistance
Annex A (Normative) Shielded cable earthing referenced drawing
Annex B (Informative) Network type earthing referenced drawing
Bibliography
Explanation of wording in this specification
