Source: https://www.scribd.com/document/65745938/RP12-16
Timestamp: 2019-08-19 01:53:16
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Matched Legal Cases: ['art 16', 'art 1', 'ARTH 4', 'art 1', 'art 1', 'art 1', 'art 3', 'art 2']

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RP 12-16 ELECTRICAL SYSTEMS AND INSTALLATIONS EARTHING AND BONDING
RP 12-16
ELECTRICAL SYSTEMS AND INSTALLATIONS EARTHING AND BONDING
(Replaces BP Engineering CP 17 part 16)
To provide guidance and information on the earthing and bonding of electrical systems, including updated standard numbers and increased information on the earthing and bonding of floating roof tanks.
CONTENTS Section Page FOREWORD .................................................................................................................. iv 1. INTRODUCTION..................................................................................................... 1 1.1 Scope .............................................................................................................. 1 2. EARTHING OF ELECTRICAL CIRCUITS AND EQUIPMENT ........................ 1 2.1 General Requirements ...................................................................................... 1 2.2 Sub-stations ..................................................................................................... 5 2.3 High-voltage Motors........................................................................................ 7 2.4 Low-voltage Equipment................................................................................... 7 2.5 Offshore Installations ....................................................................................... 7 3. LIGHTNING AND STATIC EARTHING............................................................... 8 3.1 General Requirements ...................................................................................... 8 3.2 Common Earthing System................................................................................ 9 3.3 Steel Structures (Onshore) ............................................................................... 10 3.4 Vessels and Storage Tanks............................................................................... 10 3.5 Metallic Stacks and Towers (Not applicable to Flare Stacks)............................ 13 3.6 Non-metallic Structures ................................................................................... 13 3.7 Metallic Guy Ropes ......................................................................................... 14 3.8 Pipelines and Valves......................................................................................... 14 3.9 Machine Sets with Non-electric Drive .............................................................. 15 3.10 Machine Sets with Electric Drive .................................................................. 15 3.11 Road Tanker Loading Bays........................................................................... 15 3.12 Rail Car Loading Bays .................................................................................. 16 3.13 Sea Tanker Loading Jetties ........................................................................... 16 3.14 Portable Container Filling.............................................................................. 17 3.15 Offshore Installations .................................................................................... 17 4. EARTHING SYSTEM DESIGN .............................................................................. 18 4.1 Soil Resistivity ................................................................................................. 18 4.2 Earth Electrodes .............................................................................................. 18 5. EARTHING WHERE CATHODIC PROTECTION IS APPLIED........................ 19 TABLE 1 ......................................................................................................................... 21 Typical Values Of K For Protective Conductorsand Fault Rated Bonding Connections(Based On The Iee Wiring Regulations) .............................................. 21 TABLE 2 ......................................................................................................................... 21 Minimum Cross Sectional Area Of SeparateCopper Protective Conductors And Bonding Connections(Based On The Iee Wiring Regulations)......................... 21 TABLE 3 ......................................................................................................................... 22 Conditions for Which Supplementary Bonding is not Required............................... 22 FIGURE 1A..................................................................................................................... 23 Typical Methods of Earthing ElectricalEquipment Onshore.................................... 23 FIGURE 1B..................................................................................................................... 24
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Earthing Principles Onshore................................................................................... 24 FIGURE 2A..................................................................................................................... 25 Typical Methods of Earthing ElectricalEquipment Offshore ................................... 25 FIGURE 2B..................................................................................................................... 26 Earthing Principles Offshore .................................................................................. 26 FIGURE 3 ....................................................................................................................... 27 Bonding Principles Cable Glands............................................................................ 27 FIGURE 4 ....................................................................................................................... 28 Static and Lightning Earthing Systems(Onshore) General Principles....................... 28 FIGURE 5 ....................................................................................................................... 29 Typical Earth Rod and Earth Bar Details................................................................ 29 FIGURE 6 ....................................................................................................................... 30 Typical Connections for Double Roof Tankwith 4" Outlet ..................................... 30 FIGURE 7 ....................................................................................................................... 31 Typical Connections for Double Roof Tank with6" Outlet ..................................... 31 FIGURE 8 ....................................................................................................................... 32 Typical Roof Connection for Double Roof Tank .................................................... 32 FIGURE 9 ....................................................................................................................... 33 Typical Connections for Single Roof Tank............................................................. 33 FIGURE 10...................................................................................................................... 35 Typical Roof Connection for Single Roof Tank...................................................... 35 FIGURE 11...................................................................................................................... 37 Typical Cable Detensioner ..................................................................................... 37 APPENDIX A.................................................................................................................. 38 DEFINITIONS AND ABBREVIATIONS............................................................. 38 APPENDIX B.................................................................................................................. 39 LIST OF REFERENCED DOCUMENTS ............................................................. 39
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FOREWORD Introduction to BP Group Recommended Practices and Specifications for Engineering The Introductory Volume contains a series of documents that provide an introduction to the BP Group Recommended Practices and Specifications for Engineering (RPSEs). In particular, the 'General Foreword' sets out the philosophy of the RPSEs. Other documents in the Introductory Volume provide general guidance on using the RPSEs and background information to Engineering standards in BP. There are also recommendations for specific definitions and requirements. Value of this Practice This document collates the methods and requirements for earthing and bonding of electrical systems and installations regarding both static earthing and lightning conduction. The section regarding floating roof storage tanks has been expanded in light of information received from sites. Application Text in italics is Commentary. Commentary provides background information which supports the requirements of the Recommended Practice, and may discuss alternative options. This document may refer to certain local, national or international regulations but the responsibility to ensure compliance with legislation and any other statutory requirements lies with the user. The user should adapt or supplement this document to ensure compliance for the specific application. Principal Changes from Previous Edition Generally updated and re-formatted. Additional information included regarding floating roof tanks. Feedback and Further Information Users are invited to feed back any comments and to detail experiences in the application of BP RPSE's, to assist in the process of their continuous improvement. For feedback and further information, please contact Standards Group, BP International or the Custodian. See Quarterly Status List for contacts.
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INTRODUCTION 1.1 Scope BP Group RP 12 series specify BP general requirements for electrical systems, equipment, materials and installations. This document (BP Group RP 12-16) specifies requirements for earthing and bonding of electrical and non-electrical equipment on both land-based and offshore installations. It covers earthing of electrical equipment, earthing for the control of static electricity, earthing for protection against lightning, earthing of tanks, and in certain circumstances the measures necessary to protect against 'stray' currents. The section dealing with protection against static electricity does not cover all the additional precautions which have to be observed when handling the range of products found in the petrochemical and related industries. In such cases reference should be made to relevant national, local or product specific guidance.
BS 5958 gives much detailed guidance on precautions to be taken.
Additional requirements for earthing of instrumentation and control systems are covered in BP Group RP 30-1.
BP Group RP 30-1 should also be consulted for special requirements for applications including intrinsically safe systems and electronic systems such as computers. 1.2 Quality Assurance Verification of the vendor's quality system is normally part of the pre-qualification procedure, and is therefore not specified in the core text of this specification. If this is not the case, clauses should be inserted to require the vendor to operate and be prepared to demonstrate the quality system to the purchaser. The quality system should ensure that the technical and QA requirements specified in the enquiry and purchase documents are applied to all materials, equipment and services provided by sub-contractors and to any free issue materials. Further suggestions may be found in the BP Group RPSEs Introductory Volume. 1.3 Application of Standards In the absence of relevant international equivalents, British Standards have been referenced in this document, their use does not preclude the application of equivalent national Standards where these are available.
EARTHING OF ELECTRICAL CIRCUITS AND EQUIPMENT 2.1 2.1.1 General Requirements In this document it is assumed that the power system has a neutral point at its source which is earthed directly or via a current limiting
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device. However, regardless of the method of earthing the supply, or even if the supply is not earthed, the same basic requirements for bonding will apply. For guidance on methods of earthing power systems refer to BP Group RP 12-3. 2.1.2 Onshore power earthing systems shall be designed and installed as recommended in BS 7430.
Section 4 paragraph 26 of BS 7430 mentions earthing in hazardous areas, however the following should also be noted:The minimum earth fault current required to trip the circuit follows from the tripping characteristic of the overcurrent protective device being used. In view of the fact that earth fault currents may be passing through areas classified as hazardous, along unknown routes, it is appropriate to limit strictly the time for which such a fault condition could persist as well as seeking to ensure the safety of the electrical system. Where electrical equipment is bonded to the main plant structure or directly connected to the common static and lightning earthing system, there will be many earth paths in parallel with the cable armour and the required disconnection time can normally be achieved. In other circumstances however, the earth fault current return path may be via the cable armour alone. If the cable length exceeds that which will give the required low value of earth loop impedance to trip the circuit within 5 seconds, special measures may need to be taken to reduce the earth loop impedance. In the case of a single cable, these measures may involve either increasing the cable size or providing a separate earth return conductor in addition to the cable armouring. In the case of multiple cables, each circuit should be checked to ensure that the earth loop impedance for each circuit, taking account of all cable armourings in parallel, is low enough to pass the required earth fault current.
Typical earthing and bonding installations for both onshore and offshore are shown in Fig. 1A, 1B, 2A and 2B.
The use of structural steelwork as part of an earthing current system and as a path for fault current is acceptable practice, particularly offshore where the welded steel structure of the platform is regarded as 'earth'. The term only applies to very substantial permanent structures such as an offshore platform or an onshore process plant. When a complex structure is used as (one of) the protective conductors, its impedance cannot be readily calculated. However, it can be assumed that a very large structure such as an offshore platform has negligible impedance compared with that of the cable armouring. For the purpose of calculations, the impedance of the return path through such a structure can be assumed to be zero. A consistency in the choice of protective conductor for a particular plant shall be maintained when extensions to the plant are designed.
Protective conductors may consist of one or a parallel combination of the following:
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Cable armouring or metallic sheath Rigid screwed conduit Earth core within a multicore cable Separate conductor Structural steelwork
Sole reliance on cable armouring and/or metallic sheathing shall only be made if it is adequately fault rated as a protective conductor. Note Structural steelwork may be considered as a protective conductor provided it is part of the common static and lightning earthing system and there is a permanent metallic path for fault current via such steelwork and other earthing conductors back to the source of the power supply.
This is a fundamental requirement which should be met in the case of faults within electrical equipment. In the case of faults within the cable, it may not be possible to have armour which is fully fault-rated, particularly if the armour is of the steel braid type. However, the advantages of steel braid armour over steel wire armour on cables used offshore are considered to outweigh this possible disadvantage.
The cross sectional area of every protective conductor and bonding connection between exposed and extraneous conductive parts shall be such that they are capable of carrying the earth fault current, or an appropriate fraction of the total fault current, for the duration of the fault without damage to the conductor or associated insulation. The required minimum cross sectional area may be determined by the following formula: Sp = aI t mm2 k
where, Sp I a t k = = = = = Cross-section of protective conductor (mm) Total earth fault current through the protective device (amperes) Fraction of the fault current in that part of the earth return path. Operating time of the disconnecting device (seconds) Factor dependent on the material of the conductor, the type of insulation, the assumed initial temperature and the maximum allowable temperature of the insulation
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Where electrical apparatus is required to be bonded to an earthing system, e.g. to earthed structural steelwork or buried earthing grid, any cable used for such purpose shall be sized on the assumption that it may carry the total fault current, i.e. assume a = 1. Where the 'protective conductor' consists mainly of a large steel structure such as an offshore platform, or an extensive mesh of interconnected copper earthing conductors, the impedance of the earth return path may generally be ignored for the purpose of fault current calculation. Values of k for typical types of protective conductor are given in Table 1. For conditions and conductor types not covered by Table 1, reference should be made to IEE Regulations for Electrical Installations, 16th Edition Tables 54B to 54F.
The formula is based on IEE Regulations for Electrical Installations, 16th Edition.
As an alternative to the above method of calculation, the size of copper protective conductors and associated bonding connections may be selected from Table 2. Notes: (i) (ii) Minimum size without mechanical protection shall be 4 mm2. 2.5 mm2 protective conductors shall be multistranded, i.e. 7/0.67. In practice it may be desirable for any one project, to limit the number of sizes of protective/bonding conductors to make purchasing more economical and/or to simplify design and installation.
Buried earthing conductors should normally be bare copper cable or tapes. However, if there is a likelihood of corrosion (for example particularly acidic soil) an overall protective covering, e.g. green/yellow PVC, shall be provided. Joints in protective conductors should be avoided. If this is not possible, effective measures shall be taken to prevent inadvertent disconnection, corrosion or other forms of deterioration at all such joints.
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For terminating high voltage cables, the design of the cable gland or termination shall incorporate a lug for bonding the cable armour to earth, or to the equipment enclosure. Where a low-voltage cable enters a metallic enclosure, a bonding connection between the gland and the enclosure is not required, providing there is no electrical discontinuity of the enclosure. Tapped entry holes are preferred, but where entry is through a clearance hole a 'star' washer shall be fitted under the backnut to ensure good electrical contact. Refer to Figure 3. Where plastic enclosures are used, means shall be provided to preserve the electrical continuity of the armouring and/or metallic sheaths of cables. Refer to Figure 3. Sub-stations A bar of high conductivity hard drawn (hchd) copper shall be fixed to the inside wall of the substation, to which the earth bars of all switchboards and the metallic enclosures of all low-voltage ancillary equipment (e.g. battery charger, lighting distribution board, etc.) shall be connected. The minimum size of the copper conductor shall be 75 mm2. The main substation earth bar shall be connected to one or more earthing busbars to form a complete ring. The earthing busbar(s) shall be as shown in Figure 5. Alternatively, stranded copper cable may be used to connect each item to the earthing busbars. A typical earthing layout is shown in Fig. 1A.
The star points of all Dy and similarly connected transformers and all alternator windings shall be connected to the earthing system (either directly via a current limiting impedance and/or earthing switchgear, as required by BP Group RP 12-3). Either hard-drawn high-conductivity copper bar or stranded copper cable shall be used and in either case the conductor shall have a green/yellow PVC covering. Figure 1A refers to this clause. The neutral of low-voltage three phase four wire systems shall be connected to earth via the relevant main switchboard earth bar. A bolted link shall be provided between the neutral bar and the earth bar, as detailed in BP Group GS 112-8. Figure 1A and Figure 2A refer to this clause. The tank of each main transformer shall be connected directly to an earthing bus-bar. Figure 1A refers to this clause.
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The armouring and metallic sheath (if provided) of all multicore cables shall, be bonded to the switchboard earth bar, via the termination or the gland and gland plate as detailed in BP Group GS 112-8 and GS 112-9. Figure 1A refers to this clause. Where armours and/or metallic sheaths are specified on single core cables they shall be bonded to earth at each termination unless the associated cable de-rating is unacceptable. A metallic gland plate normally provides an adequate bonding connection between the armours but care must be taken to eliminate magnetic and eddy current effects if metal gland plates are used for single core cables.
In single core cable installations the effect of load current in the cable causes magnetic fields between the conductors. Where the cable penetrates a ferrous material the magnetic field interacts to produce hysteresis so that eddy current effects which will heat up the gland plate and can lead to insulation stress. The effect can be reduced by introducing an air gap (or other means of producing high magnetic reluctance) between the cables and the eddy currents cannot flow concentrically around the cable penetration. Alternately a non ferrous gland plate could be employed. In the latter case either corrosion due to dissimilar metals needs to be considered or the method of achieving the cable sheath earth bond needs to be carefully considered. The problems associated with eddy currents and hysteresis in single core cables also affect the armour should these be ferrous. Single core cables should always have a non ferrous armour applied.
Where single point bonding is necessary unearthed termination's shall be insulated and shrouded for the maximum possible touch voltage for the application. The earthed end should be at the hazardous area end (if any). Maximum permissible sheath voltages to earth are 25V at sealing ends and 50V at joint positions. The maximum permissible substation potential rise is 430V on systems protected by overcurrent protection and 650V on systems with high speed protection. Figure 1A and Figure 2A refers to this clause.
By limiting the sheath voltage to 50 v the system safety is enhanced by complying with the provisions of a functional extra low voltage system as defined in the IEE Regulations for Electrical Installations 16th Edition. Many standards offer levels to limit the rise of earth potentials during fault conditions, the levels referenced above have been adopted as good practice by being proven safe in addition to being readily achievable.
For onshore sites, electrodes shall be installed in the ground in the vicinity of each main substation. Connections to the electrodes and rods shall be made using conductors of 70 mm2 minimum crosssectional area.
The earth electrodes are used in this case to create a reference point for the supply system. They are not generally required to carry full fault currents as all electrical supplies entering and emanating from the substation will have earth continuity
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provided (i.e. by armours and separate earth conductors). Although it is therefore less important to achieve a low electrode to earth resistance, the number and length of the earth rods shall be such as to achieve a combined electrode resistance to earth of 4 ohms or less under all soil conditions likely to occur. Figure 1A refers to this clause.
At least one more than the required minimum number of electrodes shall be installed. By this means, each electrode can be disconnected one at a time for testing without affecting the integrity of the power earthing system. All main switchboards shall be connected to the substation earthing system at two separate points. Figure 1A refers to this clause. High-voltage Motors The enclosures of all high-voltage motors shall be connected directly to the local static and lightning earthing system, or to local earth electrodes. A common earth electrode system may be used for several motors in the same area. If high-voltage motors are already in permanent electrical contact with steelwork forming part of the common earthing system, no additional copper bonding connections are required. Figure 1A refers to this clause. Metallic enclosures of the local control station and any other associated electrical devices local to the motor, shall be bonded to the motor enclosure or to the earthing system to which the motor is connected. This may be achieved through the mounting bolts and earthed steelwork. Figure 1A refers to this clause. Low-voltage Equipment If the enclosure is in permanent direct metallic contact, e.g. via pump bedplates, vessels, piping, structures, etc., with the general mass of earthed plant steelwork, there is no necessity for any further connection to any earthing system. Figure 1A refers to this clause. If the enclosure is not in permanent direct metallic contact with earthed plant steelwork or pipework, it shall be bonded to the static and lightning earthing systems or to the adjacent earthed steelwork by means of a copper conductor. Figure 1A refers to this clause. Offshore Installations Earthing shall comply generally with the IEE Regulations for the Electrical and Electronic Equipment of Mobile and Fixed Offshore Installations, Section 2.
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The enclosure of each main generator, transformer and switchboard shall be solidly bonded to the steel structure. Figure 2A refers to this clause. The requirements of sections 2.1, 2.3 and 2.4 of this Recommended Practice are also applicable, but the provisions of Figure 2A apply. The position of all earthing connections shall be visible and easily accessible. Earthing points shall be protected against corrosion. Where additional bonding connections are required, they shall be made at welded bosses local to the equipment to avoid the need for long runs. Providing that low-voltage electrical equipment is in permanent metallic contact with the general mass of earthed steelwork, no further bonding connection is required. If the protection arrangements are in accordance with Table 3.
LIGHTNING AND STATIC EARTHING 3.1 3.1.1 General Requirements The static earthing and bonding system shall be in accordance with the recommendations of BS 5958 or the equivalent national standard of the country of installation and shall be designed to take the maximum advantage of inherent earthing. The minimum amount of copper tape or conductor shall be used. In areas classified as hazardous, the relevant parts of BS 5345 or the equivalent national standard of the country of installation shall also be adhered to. All equipment and parts of equipment which are liable to accumulate potentially dangerous levels of static shall be in effective metallic contact with adjacent metal and with 'earth'. The resistance to earth from all parts of fixed metal equipment shall not exceed 10 ohms.
To prevent accumulation of static electricity, the resistance to earth may safely be as high as 108 ohms. For adequate discharge of lightning, resistances of 10 ohms or less are required. Hence for general bonding a figure of 10 ohms should be adopted in order to satisfy both lightning and static requirements.
Normal pipe and equipment flanges, unless specially insulated, provide a sufficiently low resistance to dissipate static electricity and do not require bonding connections across them. Similarly, any equipment
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which is in metallic contact with an earthed metal structure does not require any other earthing connection. Note: Earthing of fixed plant does not in all cases remove the risk of static discharge. Other precautions are also necessary such as connecting an earthing clamp to road tankers before filling, control of pumping rates, avoidance of splash filling, etc. These precautions will typically be detailed in any relevant safety codes that are applied. The detailed design of lightning protection systems should generally be in accordance with BS 6651 or the equivalent national standard of the country of installation.
Guidance is given in BS 6651 on how the requirement for lightning protection for various structures can be assessed.
In order to protect against a direct lightning stroke, as a minimum, the tallest structure on the plant shall be directly earthed as close to the base as possible with a minimum of two electrodes and the individual resistance of each shall not exceed 10 ohms. Directly earthed items shall, where possible, also be connected to the general earthing system. Structures which are made of metal and which are electrically continuous do not require a separate down conductor for lightning protection; a connection to earth at a point near the base is sufficient. Common Earthing System The requirements for protection against static electricity and lightning shall normally be met by a common earthing system to which all structures and items of process equipment are connected either directly or indirectly. The common earthing system shall comprise either of, or a combination of, the following elements: (a) (b) Buried 70 mm2 copper strip or single core copper conductor. A steel structure to which all equipment to be earthed is in direct contact or is bonded.
At onshore sites, the earthing system shall be independently connected to a number of earth electrodes (minimum of 2). Figure 4 refers to this clause.
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Where the plant is located in proximity to the process area substation, the static and lightning earthing system shall be connected to the power earthing system at two points. Steel Structures (Onshore) An earth lug or boss shall be welded to the main columns at approximately 450 mm above ground level and at intervals of not more than 30 m. Where a steel structure forms the common earthing system, or part thereof, or requires direct earthing for lightning, each earth lug or boss shall be directly connected by 50 mm copper conductor tape to an adjacent earth electrode. Where the steel structure does not form part of the common earthing system and does not require direct earthing for lightning, each lug or boss shall be connected by 35 mm copper conductor to the common earthing system. Figure 4 refers to this clause. Vessels and Storage Tanks Vessels When mounted directly on and in metallic contact with an earthed steel structure, no further bonding is necessary other than that which may be necessary for lightning protection. When the mounting is insulated from steelwork by materials having poor conductivity such as wood, concrete, rubber etc., two earthing connections shall be taken from the vessel to the common earthing system. Where the vessel is so remote from the plant as to make connection to the common earthing system impractical, two connections shall be taken from the vessel to separate earth electrodes and the resistance to earth of each electrode shall not exceed 10 ohms. Figure 4 refers to this clause. Looping of earthing conductors between vessels is permitted provided a connection is taken from each end of the 'looped' system to the general earth system or earth electrodes. Direct earthing for lightning shall be applied if necessary.
When vessels are mounted in accordance with 3.4.1.1 and the minimum value of 10 ohms is not achieved, additional earthing is required.
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Earthing connections shall be 35 mm2 copper conductor except for direct earthing connections for lightning which shall be 50 mm2 copper conductor. Where a vessel has insulation and an outer metal cladding or wire reinforcement, the metal cladding or reinforcement shall be electrically continuous and bonded to the vessel. Figure 4 refers to this clause. The armouring of cables which enter the vessel shall be bonded to the shell at the point of entry. Storage Tanks Tanks up to 30 m diameter shall be provided with two, and tanks over 30 m diameter shall be provided with three, equally spaced earthing bosses. The bosses shall be positioned near the base of the tank and be in accordance with Figure 1A. The earthing lugs or bosses on the tank shall be connected to the same number of separate earth electrodes as there are lugs or bosses, either individually or on a shared basis. The earth electrodes should preferably be close to the tank base. For a group of tanks, earth electrodes common to the group may be installed provided that each tank has, as a minimum, two paths to earth. This ensures that during testing of one electrode, the tank will remain earthed by a system with an earth resistance not exceeding 10 ohms. All tank internals, e.g. mixers, gauge floats and sling arms, shall be bonded to the tank shell at one or more locations depending on the size of the internal object.
Bonding can preferably be achieved by direct bolting. Care should be taken to avoid the formation of re-entrant loops.
On floating roof tanks, multiple shunt connections comprising stainless steel strips 50 x 0.6 x 400 mm long, shall be provided between the floating roof and the tubbing shoe at adequate intervals around the roof periphery or one per pantograph where these are fitted. Where high winds prevail the shunt strips may be replaced with cables bolted in position. Shunts should be fitted above the sealing arrangement. The spacing of shunt connections should avoid the risk of discharge from the roof to the tank wall directly across the gap rather than via a shunt, due to the formation of re-entrant loops. BS 6651 gives guidance that the risk is increased when the path length of the loop exceeds eight time the width of the open side. In this case the
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maximum loop length is half the peripheral distance of the closed path between adjacent shunts.
Although hanger linkages on the pantograph offer an earthing path from the floating roof to the shell they can be a source of arcs during a lightning strike if placed too close together (accepted minimum on an empirical basis is 1 m). The arcs occur from sharp points or joints. The arcs may be avoided by installation of a short insulated jumper around each pinned hanger joint together with covering sharp points of hangers with insulating material.
When a rolling ladder is fitted, a 35 mm2 flexible copper bonding conductor shall be applied across the ladder hinges, between the ladder and the tank top, and between the ladder and the floating roof. (This is in addition to earthing required in 3.4.2.5)
The earthing provisions assume the ladder is articulated in the centre in a manner which allows continuity of earthing. Where there may be appreciable movement of the ladder at either the roof or rim which makes earth bonding non feasible, another approach entirely may be necessary. No specific advice is available for this eventuality but past instances have led to arrangements which stowed ladders away from the roof when not in use.
When a rolling ladder is not fitted a flexible earth cable of 70 mm2 cross-section shall be installed along the roof drain of the tank. Instructions regarding installation of these cables is included in 3.4.3. (This is in addition to earthing required in 3.4.2.5)
Previously, fitting of flexible earthing cable between the floating roof and tank shell was practised as a supplement to the pantograph earthing system. However, experience showed that these cables frequently became entangled and broke with the movement of the roof. Also, the tangling of the cable produced re-entrant loops. Thus, this practice is no longer recommended.
As an alternative to the provisions of 3.4.2.7 lightning protection can be achieved using an air termination network as described in clause 21.2 of BS 6651. Floating Roof Tanks without Rolling Ladders Figures 6 - 11 give suggested typical details for earthing floating roof tanks when no rolling ladder is fitted. Earthing of the roof should be provided by 70 mm2 flexible earth cables (e.g. neoprene covered) laid along the roof drain. One earth cable should be installed for each roof drain. schemes are shown in Figures 6, 7 and 9. Typical
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Suggested Roof connections for double and single roof tanks are shown in Figures 8 and 10. The connections should be to a similar material specification to that for the tank itself. Roof connections should be sited close to the roof drains with suitable facilities to securely fix the earth cable to the roof. All connections should be protected against corrosion. At the point where the earth cable exits the roof connection a detensioner (see Figure 11) should be fitted. The earth cable should then be fixed to the roof drain using suitable clips (e.g. stainless steel cable ties) with due allowance for movement of all swivels. Once earthing cables have been installed, tests should be undertaken to ensure there is a low resistance (less than 0.1 ohm) between the roof and the wall. Metallic Stacks and Towers (Not applicable to Flare Stacks) Provided they are of welded, bolted or riveted construction, no air terminals or down conductors are required. Figure 4 refers to this clause. Two earth lugs or bosses near to the ground, on opposite sides of the equipment, shall be provided and independently connected either to the general earthing system or to two earth electrodes near to the base of the equipment. The method used shall depend on the need for protection against direct lightning strokes. The armouring of all cables which enter metallic stacks shall be bonded to the stack at the point of entry. Figure 4 refers to this clause. Non-metallic Structures In all areas classified as hazardous, steelwork such as stairways, cable racks, handrails, etc., which is mounted on or attached to non-metallic structures shall be bonded to the general earthing system either directly or via other earthed metal at intervals not exceeding 30 m. If such steelwork is not already bonded as an extraneous conductive part (IEE wiring regulations) then as an alternative to bonding, an assessment shall be carried out to ensure:(a) that the steelwork is sufficiently isolated from other potential lightning discharge carrying conductors to ensure no side flashing will occur, guidance is given in BS 6651.
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no static build up above the minimum ignition energy of hydrocarbons present is possible, guidance given in BS 5958 Part 1.
Non-metallic structures less than 9 m in height do not generally require lightning protection or earthing. If greater than 18 m in height, they shall be provided with lightning protection. Figure 4 refers to this clause. The need for lightning protection on non-metallic structures between 9 m and 18 m in height shall be determined taking into account the heights of other adjacent structures, the nearness of flammable materials, consequences of damage, etc. BS 6651 or the equivalent national standard of the country of installation should be referred to for guidance. Metallic Guy Ropes Metallic guy ropes used for supporting metallic or non-metallic stacks or other structures shall be bonded at their upper ends to the stack or structure if metallic, or to the lightning protective system in the case of non-metallic stacks or structures. The lower end of each guy rope shall be directly earthed. Where a guy rope is comprised of two ropes in parallel, they shall be bonded together at the upper and lower ends and then treated as one rope. Figure 4 refers to this clause. Pipelines and Valves It is not necessary to bond across the flanges of pipe joints, nor is it normally necessary to earth pipelines separately, since adequate earthing is provided via the vessels and other equipment to which the pipes are connected. However, long pipelines crossing open ground shall be earthed at or near any plant boundary. The spindles of all ball valves will need to be bonded to their pipeline only where the ball valve is controlling a two phase mixture, and where the valve is not fitted with a special earthing washer, or where the valve is immediately downstream of fine filtration facilities. Charge generation is increased in a two phase mixture due to the increased surface area of the individual phases, and is increased downstream of fine filters due to extensive charge separation.
An exception to 3.8.1 shall be made in areas where liquefied petroleum gas is handled such as tanker loading bays. Particular attention should be paid to earthing across flexible connections. As LPG is normally contained in closed systems there is no danger under these conditions as the gas concentration will be well above the
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upper flammable limit. The release and/or rapid expansion of LPG results in the formation of a mist which is capable of generating static electricity. Danger only exists therefore where LPG is handled, and there is the risk of static build up if all metallic parts are not adequately bonded. 3.8.3 For earthing associated with cathodically protected pipelines, reference should be made to Section 6 of this Recommended Practice. Machine Sets with Non-electric Drive When driving and driven machines are in direct metallic contact with an earthed steel structure, no further earthing is required. When the driving and driven machines are bolted to a common metallic bedplate which is on a concrete or other poorly conducting foundation, one connection shall be taken from the bedplate to the general earthing system. Figure 4 refers to this clause. When the driving and driven machines are on separate bedplates mounted on separate concrete plinths or other poorly conducting material, the bedplates shall be bonded together and one connection shall be taken to the general earthing system. Figure 4 refers to this clause. All earth connections shall be 35 mm2 copper conductor. Machine Sets with Electric Drive No specific earthing connection is required if the driven machine is mounted on a metallic bedplate providing for the dissipation of static. Figure 4 refers to this clause. Road Tanker Loading Bays Each loading gantry shall have a connection to earth at each end of the gantry. The connections may be direct to independent earth electrodes or to the general earthing system of adjacent plant. The individual resistance to earth of the connections to the earthing system shall not exceed 10 ohms. All product pipelines shall be bonded to the loading gantry either by means of pipe clamps or pipe flange bolts. All loading hoses shall be electrically continuous from the product pipeline to the loading nozzle or flange. A bond shall be installed across each swivel joint in metallic loading arms.
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Each loading bay shall be provided with a number of flexible connections of 35 mm2 copper which are bolted to an earth boss in the loading gantry at one end, and which have a robust earthing clamp of an approved type for the other end for bonding the tanker to earth during loading and discharge. For LPG loading bays, the earthing arrangements for the vehicle shall ensure that the earth connection shall be completed in an area classified as non hazardous or via an earthing switch in a suitably certified enclosure. Earth proving devices and interlock arrangements shall be provided so that tanker loading or discharge is possible only when effective earthing has been achieved. All connections to earth shall be 35 mm2 stranded copper conductor. Rail Car Loading Bays The requirements of 3.11 of this Recommended Practice apply, except that a flexible cable connection is not required since the contact between the tanker wheels and the track provides sufficient earthing. All rails shall be bonded together and connected to the loading gantry or earthing system. To guard against stray currents, insulated joints shall be inserted in the rails to isolate those in the loading gantry from the remainder of the rail system. On electrified rail systems the live contact rails or overhead conductors shall terminate outside the loading compound. Sea Tanker Loading Jetties The earthing and bonding system on tanker loading jetties shall comply generally with the International Safety Guide for Oil Tankers and Terminals. The loading arms on all jetties shall have an insulated flange inserted in the 'outboard' end of the loading arm to prevent flows of stray current along the loading arm and hence potential sparking when the connection is made. That section of the loading arm which is 'downstream' of the flange shall be connected to the ship and the 'upstream' section connected to the jetty earthing system.
3.11.7 3.12 3.12.1
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For jetties using hose loading gantries, the jib handling rig hook shall be insulated. Breasting dolphins, fenders and quays having metallic parts connected to the jetty earthing system shall be protected from direct contact with ships hulls, e.g. by wooden linings. Mooring dolphins shall be insulated from the jetty earthing system or located in a safe area but insulated from the shore earthing system. Insulating flanges shall be inserted in each pipeline at the shore end. The jetty structure and earthing system should also be isolated from the shore earthing system. In the case of steel jetties which have impressed current cathodic protection, cables entering the jetty area from the shore should have their metallic sheaths and/or armours bonded to the jetty earthing system but isolated from the shore earthing system at the shore end. Where this connection presents excessive diversion of impressed current, resulting in the protection potential not being maintained, an alternative insulation arrangement shall be utilised.
It is no longer considered safe practice to bond the tanker to the jetty earthing system, because of potential difference which may exist due to cathodic protection of the ship's hull and/or the jetty structure. When such a bond is broken, an incendive spark can be produced. (See International Safety Guide for Oil Tankers and Terminals). The resistance across insulated flanges should be at least 25 x 103 ohms when new, but in service a resistance as low as 103 ohms is acceptable. Periodic measurements of the insulation resistance should be carried out with a multi-meter, which should be of a type of protection suitable for the classification of the area. See BP Group RP 12-2 for guidance.
Portable Container Filling In addition to the earthing of items already mentioned in this section, the following shall be electrically continuous and bonded to the common earthing system or to an earthing system installed specifically for the filling installation: (i) (ii) (iii) Weighing machine platforms and bases Conveyor tracks Any other ancillary equipment.
Filling hoses shall be electrically continuous. A separate flexible earthing lead with a robust clip or clamp shall be provided for connecting to the drum during filling, although such an arrangement is not necessary for the filling of pressure containers.
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An earth proving unit, interlocked with the product delivery pumps shall be installed. 3.15 3.15.1 Offshore Installations All plant which is not in metallic contact with earthed structural steelwork shall be bonded to the platform steelwork. A separate earthing system for lightning and static protection is not required. A reel of single core flexible cable, minimum size 35 mm, shall be installed in an area classified as non-hazardous by the helideck, for bonding helicopters to the platform during refuelling. The reel shall incorporate a slip ring to pick up the connection to earth.
EARTHING SYSTEM DESIGN 4.1 4.1.1 Soil Resistivity The resistance of an earth electrode of given dimensions and geometry is dependent on the soil resistivity, which varies according to the type of soil, moisture content, degree of compaction and chemical composition. Specific guidance on soil resistivities for various types of soil is given in BS 7430, Table 1. Resistivity measurements shall be made at the proposed electrode locations. These measurements and the subsequent electrode design should be carried out at an early stage of the project so that the electrode locations are compatible with plot layouts, foundations, etc. Where there is any option, a site should be chosen for the electrodes which is not naturally well drained. However the ground need not be water-logged. Locations where the ground is kept moist by water flowing over it should be avoided. Wherever possible, dry, sandy or rocky ground should also be avoided. The effect of possible seasonal increases in electrode resistance due to drying out or freezing of the ground shall be taken into account. Wherever possible, the earth electrode should be installed deep enough to reach the water table or permanent moisture level, deeper than frost is likely to penetrate and to reach stable ground conditions. Bentonite or similar material may be used to improve contact efficiency in difficult ground conditions.
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Earth Electrodes Earth electrodes shall normally consist of a number of rod sections coupled together and driven vertically into the ground. A number of such rods may need to be connected in parallel to obtain the required electrode resistance. The distance between rods should be greater than their depth.
In soils of uniform resistivity, it is more economical to install a number of rods connected in parallel than to attempt to obtain the required resistance from a single deeply driven rod. However if the rods are driven too closely together, their effectiveness is reduced. In practice, a separation of less than 3m should be avoided.
Earthing materials shall comply generally with the requirements of BS 6651 or the equivalent national standard of the country of installation. Earth rods may be of the following materials providing that they are entirely suitable for the application and ground conditions: (i) (ii) (iii) (iv) (v) (vi) solid hard drawn copper phosphor bronze copper clad steel stainless steel galvanised steel. cast iron pipe
Earth rods are generally available in standard lengths of at least 1.22 m. Copper clad steel rods are available in lengths up to 3 m. The minimum diameter shall be 15 mm. 4.2.4 Copper clad steel rods shall be of the molecularly bonded type. The thickness of copper shall be 0.25 mm minimum and the coating shall be maintained over the entire length of the rod including the threaded portion. Couplings shall be made of silicone aluminium bronze and shall be of sufficient length to enclose completely the threads with the rods in end-to-end contact. Each earth rod shall be protected against corrosion and terminated in an inspection pit complying with Figure 5.
EARTHING WHERE CATHODIC PROTECTION IS APPLIED 5.1 Cathodic protection system design shall comply generally with BS 7361 Pt 1. Attention is drawn particularly to 12.3.1 and 12.4 of BS 7361 Pt 1.
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Bonding between a cathodically protected pipeline or storage tank, etc., and any earthing system can reduce the efficiency of an impressed current cathodic protection system by diverting the flow of impressed current. As far as possible, the cathodically protected sections of pipeline should be isolated from unprotected sections and from any earthing systems, although the presence in the line of electrically operated valves may make complete isolation impractical. Isolation can be achieved when electrically operated valves or other devices are installed by inserting insulating bushes between the cable gland and the device. In this case the device should be bonded to the pipeline. It should be established however that a return earth path via the pipeline is sufficient to ensure correct operation of protective devices on the supply to the equipment. Sometimes it is necessary to earth buried pipelines which are impressed current cathodically protected, e.g. to alleviate the effects of local overhead power lines. In such cases the pipeline should be earthed by polarisation cells or alternatively by the use of earthing rod materials of a suitable galvanic potential.
Where plant is cathodically protected, either by sacrificial anodes or by an impressed current system, the design of the earthing systems shall be agreed with the suppliers and designers of the cathodic protection system.
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Material of Protective Conductor Copper with PVC sheath Bare copper Copper as a core of a PVC cable Copper as a core of an EPR cable Steel armour in contact with PVC Lead sheath in contact with PVC Bare steelwork
Assumed Initial Temperature C 30 30 70 85 60 60 30
Final Temp.C 160 200 160 220 200 200 200
k 143 159 115 134 51 26 58
TABLE 1 Typical Values Of K For Protective Conductorsand Fault Rated Bonding Connections (Based On The IEE Wiring Regulations)
Cross-sectional Area of Associated Current Carrying Conductor mm 1.0 1.5 2.5 4 6 10 16 25 35 50 70 95 120 and over
Minimum Cross-sectional Area of Copper Earthing/Bonding Connection mm 2.5 See Notes 2.5 } In 2.5 (i) & (ii) Para 2.1.6 4 6 10 16 16 16 25 35 50 70
TABLE 2 Minimum Cross Sectional Area Of SeparateCopper Protective Conductors And Bonding Connections (Based On The IEE Wiring Regulations)
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System Voltage 110V up to and including 440V 55-0-55 V
Protection arrangements not requiring supplementary bonding Protective device rating 32 A or less; or RCD protected. Fuse rating 16 A or less; or MCB rating 32 A or less; or RCD protected. Fuse rating 6 A or less; or MCB rating 10 A or less; or RCD protected.
TABLE 3 Conditions for Which Supplementary Bonding is not Required (Based on the IEE Recommendations for the Electrical and Electronic Equipment of Mobile and Fixed Offshore Installations)
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NUMBERS SHOWN THUS 2.2.1 INDICATE THE RELEVANT CLAUSE IN THE TEXT. FOR EARTHING DETAILS SEE FIG 5.
FIGURE 1A Typical Methods of Earthing Electrical Equipment Onshore
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NOTES: 1. APPARATUS WHICH IS BONDED TO AN EARTHED STEEL STRUCTURE BY MEANS OF ITS HOLDING DOWN BOLTS OR BY WELDING REQUIRES NO ADDITIONAL BONDING CONNECTION. 2. APPARATUS WHICH IS OTHERWISE ISOLATED FROM THE EARTHING SYSTEM SHOULD BE BONDED AS SHOWN. THE CROSS SECTION OF THE EARTH BOND SHOULD BE IN ACCORDANCE WITH SUB-SECTION 2.1.5 OR 2.1.6. 3. WHERE THE PLANT/APPARATUS IS REMOTE FROM THE SUB-STATION THE EARTHING SYSTEMS NEED NOT BE INTERCONNECTED. IN THIS CASE EARTH FAULT CURRENT WILL RETURN VIA THE CABLE ARMOUR OR EARTH CORE. ACCOUNT SHOULD BE TAKEN OF PARALLEL EARTH PATHS VIA THE ARMOUR OF OTHER CABLES.
FIGURE 1B Earthing Principles Onshore
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FIGURE 2A( PAGE 1 OF 2 ) Typical Methods of Earthing Electrical Equipment Offshore
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NOTES 1. FIXED OFF SHORE INSTALLATIONS ARE GROUNDED OR EARTHED INTO THE SEABED BY STEEL PIPES, WELL CONDUCTORS ETC. MOBILE UNITS ARE EARTHED BY THE CONDUCTIVITY OF THE SEAWATER 2. ALL TOPSIDES METALWORK IS EITHER BOLTED OR WELDED ONTO THE STRUCTURAL SUPPORT STEELWORK TO EXTEND THE EARTH CONTINUITY TO THE EXTREMEITIES OF THE INSTALLATION. 3. ALL TANKS, VESSELS,PIPE DUCT & TRAYWORK, HANDLING & ACCESS WAYS ARE BOLTED OR WELDED TO THE STRUCTURAL STEELWORK TO ENSURE THAT ANY STATIC POTENTIAL BUILD UP WILL BE AVOIDED BY CONTINUOUS DRAIN TO EARTH 4. ALL LIVE CONDUCTORS ARE PROTECTED AGAINST TOUCHING BY PERSONNEL, CORROSION AND POSSIBLE MECHANICAL DAMAGE 5. ALL METALLIC ENCLOSURES, GLAND PLATES & CABLES GLANDS HAVE EARTH CONTINUITY BY PHYSICAL CONNECTION. 6. ALL INSULATED ENCLOSURES HAVE EARTH CONTINUITY FACILITY FOR INTERNAL METAL WORK, VIA CABLE ARMOURING SYSTEM. 7. NEUTRALS OF LV SYSTEMS ARE EARTHED AT THE SWITCHBOARD 8. EXPOSED METALLIC PARTS OF ELECTRICAL EQUIPMENT ARE IN ELECTRICAL CONTACT WITH THE STRUCTURE BY HOLDING DOWN BOLTS, BEDPLATES ETC, BUT ADDTIONAL BONDING CONNECTIONS ARE REQUIRED WHERE INDICATED 9. NUMBERS SHOWN THUS :- 2.2.1 INDICATE THE RELAVENT CLAUSE IN THE TEXT. 10. THIS DRAWING IS BASED ON FIG 2.1 OF THE IEE RECOMMENDATIONS FOR THE ELECTRICAL & ELECTRONIC EQUIPMENT OF MOBILE & FIXED OFFSHORE INSTALLATIONS.
FIGURE 2A( PAGE 2 OF 2 ) Typical Methods of Earthing Electrical Equipment Offshore
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FIGURE 2B( PAGE 1 OF 2 ) Earthing Principles Offshore
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NOTES 1. THE STEEL STRUCTURE OF THE PLATFORM JACKET & MODULES FORMS THE EARTHING SYSTEM & THE PRINCIPLE PROTECTIVE CONDUCTOR 2. EXPOSED METALLIC PARTS OF ELECTRICAL ( & NON ELECTRICAL ) APPARATUS ARE NORMALLY EFFECTIVILY BONDED TO THE STEEL STRUCTURE BY HOLDING DOWN BOLTS, BEDPLATES WELDS ETC BUT ADDTIONAL BONDING CONNECTIONS ARE REQUIRED WHERE INDICATED 3. ALL TANKS, VESSELS . PIPES, DUCTS, TRAYWORK, HANDRAILS, ETC. ARE BOLTED OR WELDED TO THE STEEL STRUCTURE ENSURING ELECTRICAL CONTINUITY THROUGHTOUT INSTALLATION & PREVENTING ANY BUILD UP OF STATIC. 4. ARROWS INDICATE ROUTE OF CURRENT FOR EARTH FAULT AT POINT F IN ADDTION FAULT CURRENT WILL RETURN VIA PIPEWORK & THE ARMOURING OF OTHER CABLES.
FIGURE 2B( PAGE 2 OF 2 ) EARTHING PRINCIPLES OFFSHORE
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NOTES 1. WHERE CABLES ENTER A METALLIC ENCLOSURE IT IS NOT NECESSARY TO INSTALL ADDTIONAL BONDING CONNECTIONS BETWEEN GLANDS OR BETWEEN GLANDS AND THE EQUIPMENT, PROVIDED THAT THE ENTRY IS TAPPED OR A STAR WASHER IS FITTED UNDER THE BACKNUT TO ENSURE GOOD ELECTRICITY 2. WHERE CABLES ENTER A NON-METALLIC ENCLOSURE MEANS SHOULD BE PROVIDED EITHER INTERNALLY OR EXTERNALLY FOR BONDING THE CABLE ARMOUR TO EACH OTHER & TO EARTH. ( THIS IS NORMALLY ACHIEVED WITH AN EARTH CONTINUITY PLATE INTERNALLY ON THE ENCLOSURE ).
FIGURE 3 Bonding Principles Cable Glands
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NOTES 1. NUMBERS SHOWN THUS 3.4.1 REFER TO THE RELAVENT CLAUSE OF THE TEXT 2. FOR EARTHING DETAILS REFER FIG 5 3. THIS DIAGRAM IS INTENDED TO ILLUSTRATE A TYPICAL STATIC AND LIGHTING EARTHING SCHEME. IN PRACTICE THE DESIGN OF THE EARTHING SYSTEM WILL DEPEND ON SITE CONDITIONS, SOIL RESISTIVITY, PLANT LAYOUT, NEED FOR LIGHTING PROTECTION,ETC
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FIGURE 4 Static and Lightning Earthing Systems (Onshore) General Principles
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FIGURE 5 ( PAGE 1 OF 2 ) Typical Earth Rod and Earth Bar Details
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NOTES 1. CONDUCTORS MINIMUM SIZE & TYPE OR EARTH CONDUCTOR FOR GENERAL USE SHALL BE 25 x 3 COPPER TAPE OR 70mm2 BARE COPPER CABLE MINIMUM SIZE & TYPE OF FLEXIBLE EARTH CONDUCTOR SHOULD BE 35mm2 276/0 SINGLE CORE 600/1000 VOLT GRADE. WHILST COPPER CONDUCTORS ARE PREFERRED OTHER EQUVALANT MATERIALS MAY BE USED SUBJECT TO APPROVAL FOR MECHANICAL PROTECTION OR WHERE CORROSIVE CONDITIONS MAY EXIST AN OVERALL COVERING, eg PVC, SHALL BE PROVIDED 2. WHERE RODS CANNOT BE DRIVEN TO A SUITABLE DEPTH THEIR INSTALLATION MUST BE PRECEDED BY DRILLING. CARE MUST BE TAKEN TO ENSURE THE SATISFACTIRY CONSOLIDATION OF THE BACKFILL SOIL RESISTIVITY CAN BE REDUCED BY THE USE OF A SUITABLE SOIL CONDITIONING AGENT. SALT B AGENT SHOULD BE AVOIDED AS THEY ENCOURGE CORROSION. 3. THE USE OF CLADWELD JOINTING TECHNIQUE IS PERMITTED FOR THE EARTH CONDUCTOR JOINTS, AND IS THE PREFERRED METHOD FOR UNDERGROUND JOINTS. 5. EARTHING BOSSES WELDED TO PRESURISED VESSELS SHALL BE OF THE SAME MATERIAL QUALITY AS THE VESSEL
FIGURE 5 ( PAGE 2 OF 2 ) Typical Earth Rod and Earth Bar Details
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FIGURE 6 Typical Connections for Double Roof Tank with 4" Outlet
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FIGURE 7 Typical Connections for Double Roof Tank with 6" Outlet
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FIGURE 8 Typical Roof Connection for Double Roof Tank
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FIGURE 9 Typical Connections for Single Roof Tank
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FIGURE 10 Typical Roof Connection for Single Roof Tank
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FIGURE 11 Typical Cable Detensioner
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APPENDIX A DEFINITIONS AND ABBREVIATIONS Definitions Standardised definitions may be found in the BP Group RPSEs Introductory Volume. bonding: an electrical connection between 'exposed' and/or 'extraneous' conductive parts to equalise their potential. Two metallic parts which are welded or solidly bolted together so as to form a permanent conductive path across the joint or through the bolts may be considered to be 'bonded'.
particular attention shall be given to the potential for deterioration of bolted connections due to corrosion. Most welding techniques and bolted lugs are usually found to be entirely satisfactory.
a conductive part of electrical equipment which can be touched and which is not live but may become live under fault conditions.
extraneous conductive parts: exposed metal parts of other services or of a structure which are normally at earth potential. high voltage: a system whose voltage exceeds 1000 V a.c. or 1500 d.c. between conductors. a system whose voltage does not exceed 1000 V a.c. or 1500 V d.c. between conductors. a conductor connecting exposed or extraneous conductive parts to the earthed point of the source, to provide a return path for fault current.
Abbreviations BS EN IEC IEE IP ISO PVC SI British Standard European Standard International Electrotechnical Commission Institution of Electrical Engineers Institute of Petroleum International Standards Organisation Polyvinyl Chloride Systeme International d'Unites
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APPENDIX B LIST OF REFERENCED DOCUMENTS A reference invokes the latest published issue or amendment unless stated otherwise. Referenced standards may be replaced by equivalent standards that are internationally or otherwise recognised provided that it can be shown to the satisfaction of the purchaser's professional engineer that they meet or exceed the requirements of the referenced standards. International Codes and Standards International Safety Guide for Oil Tankers and Terminals (Compiled by International Chamber of Shipping/Oil Companies International Marine Forum/International Association of Ports and Harbours) British Codes and Standards BS 5345 Code of practice for the selection, installation and maintenance of electrical apparatus for use in potentially explosive atmospheres (other than mining applications or explosive processing and manufacture). Code of Practice for the control of undesirable static electricity. Protection of structures against lightning. Cathodic protection part 1. Code of practice for land and marine applications. (Formerly CP 1021) Code of Practice for Earthing (Formerly CP 1013 : 1965)
BS 5958 BS 6651 BS 7361 Pt 1
BS 7430 UK Industry Standards IP
Institute of Petroleum Model Code of Safe Practice: Part 1 Electrical. Regulations for Electrical Installations (Wiring Regulations). 16th Edition. Recommendations for the Electrical and Electronic Equipment of Mobile and Fixed Offshore Installations.
ELECTRICAL SYSTEMS AND INSTALLATIONS EARTHING AND BONDING PAGE 41
BP Group Documents BP Group RP 12-2 Electrical Equipment in Combustible Dusts (replaces BP CP 17 Part 1) Power System Design (replaces BP CP 17 Part 3) Instrumentation (replaces BP CP 18 Part 2) Petroleum and Petrochemical Storage (replaces BP CP 21) High-voltage Switchgear and Control Gear (replaces BP Std 225) Low-voltage Switchgear and Control Gear (replaces BP Std 227) Flammable Atmospheres and
BP Group RP 12-3
BP Group RP 30-1
BP Group RP 58-1
BP Group GS 112-9
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