bp rec om ended practice electrical system and installation earthing bonding

RP 12-16

ELECTRICAL SYSTEMS ANDINSTALLATIONS

EARTHING AND BONDING

February 1994

Copyright © The British Petroleum Company p.l.c.

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Copyright © The British Petroleum Company p.l.c.All rights reserved. The information contained in this document is subjectto the terms and conditions of the agreement or contract under which thedocument was supplied to the recipient's organisation. None of theinformation contained in this document shall be disclosed outside therecipient's own organisation without the prior written permission ofManager, Standards, BP International Limited, unless the terms of suchagreement or contract expressly allow.

BP GROUP RECOMMENDED PRACTICES AND SPECIFICATIONS FOR ENGINEERING

Issue Date February 1994Doc. No. RP 12-16 Latest Amendment Date

Document Title

ELECTRICAL SYSTEMS ANDINSTALLATIONS

EARTHING AND BONDING(Replaces BP Engineering CP 17 part 16)

APPLICABILITY

Regional Applicability: International

SCOPE AND PURPOSE

To provide guidance and information on the earthing and bonding of electrical systems,including updated standard numbers and increased information on the earthing andbonding of floating roof tanks.

AMENDMENTSAmd Date Page(s) Description___________________________________________________________________

CUSTODIAN (See Quarterly Status List for Contact)

ElectricalIssued by:-

Engineering Practices Group, BP International Limited, Research & Engineering CentreChertsey Road, Sunbury-on-Thames, Middlesex, TW16 7LN, UNITED KINGDOM

Tel: +44 1932 76 4067 Fax: +44 1932 76 4077 Telex: 296041

RP 12-16ELECTRICAL SYSTEMS AND INSTALLATIONS

EARTHING AND BONDINGPAGE i

CONTENTSSection Page

FOREWORD .................................................................................................................. iv

1. INTRODUCTION..................................................................................................... 11.1 Scope .............................................................................................................. 1

2. EARTHING OF ELECTRICAL CIRCUITS AND EQUIPMENT ........................ 12.1 General Requirements ...................................................................................... 12.2 Sub-stations ..................................................................................................... 52.3 High-voltage Motors........................................................................................ 72.4 Low-voltage Equipment................................................................................... 72.5 Offshore Installations ....................................................................................... 7

3. LIGHTNING AND STATIC EARTHING............................................................... 83.1 General Requirements ...................................................................................... 83.2 Common Earthing System................................................................................ 93.3 Steel Structures (Onshore) ............................................................................... 103.4 Vessels and Storage Tanks............................................................................... 103.5 Metallic Stacks and Towers (Not applicable to Flare Stacks)............................ 133.6 Non-metallic Structures ................................................................................... 133.7 Metallic Guy Ropes ......................................................................................... 143.8 Pipelines and Valves......................................................................................... 143.9 Machine Sets with Non-electric Drive .............................................................. 153.10 Machine Sets with Electric Drive .................................................................. 153.11 Road Tanker Loading Bays........................................................................... 153.12 Rail Car Loading Bays .................................................................................. 163.13 Sea Tanker Loading Jetties ........................................................................... 163.14 Portable Container Filling.............................................................................. 173.15 Offshore Installations .................................................................................... 17

4. EARTHING SYSTEM DESIGN .............................................................................. 184.1 Soil Resistivity ................................................................................................. 184.2 Earth Electrodes .............................................................................................. 18

5. EARTHING WHERE CATHODIC PROTECTION IS APPLIED........................ 19

TABLE 1 ......................................................................................................................... 21Typical Values Of K For Protective Conductorsand Fault Rated BondingConnections(Based On The Iee Wiring Regulations) .............................................. 21

TABLE 2 ......................................................................................................................... 21Minimum Cross Sectional Area Of SeparateCopper Protective ConductorsAnd Bonding Connections(Based On The Iee Wiring Regulations)......................... 21

TABLE 3 ......................................................................................................................... 22Conditions for Which Supplementary Bonding is not Required............................... 22

FIGURE 1A..................................................................................................................... 23Typical Methods of Earthing ElectricalEquipment Onshore.................................... 23

FIGURE 1B..................................................................................................................... 24


EARTHING AND BONDINGPAGE ii

Earthing Principles Onshore................................................................................... 24

FIGURE 2A..................................................................................................................... 25Typical Methods of Earthing ElectricalEquipment Offshore ................................... 25

FIGURE 2B..................................................................................................................... 26Earthing Principles Offshore .................................................................................. 26

FIGURE 3 ....................................................................................................................... 27Bonding Principles Cable Glands............................................................................ 27

FIGURE 4 ....................................................................................................................... 28Static and Lightning Earthing Systems(Onshore) General Principles....................... 28

FIGURE 5 ....................................................................................................................... 29Typical Earth Rod and Earth Bar Details................................................................ 29

FIGURE 6 ....................................................................................................................... 30Typical Connections for Double Roof Tankwith 4" Outlet ..................................... 30

FIGURE 7 ....................................................................................................................... 31Typical Connections for Double Roof Tank with6" Outlet ..................................... 31

FIGURE 8 ....................................................................................................................... 32Typical Roof Connection for Double Roof Tank .................................................... 32

FIGURE 9 ....................................................................................................................... 33Typical Connections for Single Roof Tank............................................................. 33

FIGURE 10...................................................................................................................... 35Typical Roof Connection for Single Roof Tank...................................................... 35

FIGURE 11...................................................................................................................... 37Typical Cable Detensioner ..................................................................................... 37

APPENDIX A.................................................................................................................. 38DEFINITIONS AND ABBREVIATIONS............................................................. 38

APPENDIX B.................................................................................................................. 39LIST OF REFERENCED DOCUMENTS............................................................. 39


EARTHING AND BONDINGPAGE iv

FOREWORD

Introduction to BP Group Recommended Practices and Specifications forEngineering

The Introductory Volume contains a series of documents that provide an introductionto the BP Group Recommended Practices and Specifications for Engineering (RPSEs).In particular, the 'General Foreword' sets out the philosophy of the RPSEs. Otherdocuments in the Introductory Volume provide general guidance on using the RPSEsand background information to Engineering standards in BP. There are alsorecommendations for specific definitions and requirements.

Value of this Practice

This document collates the methods and requirements for earthing and bonding ofelectrical systems and installations regarding both static earthing and lightningconduction.

The section regarding floating roof storage tanks has been expanded in light ofinformation received from sites.

Application

Text in italics is Commentary. Commentary provides background information whichsupports the requirements of the Recommended Practice, and may discuss alternativeoptions.

This document may refer to certain local, national or international regulations but theresponsibility to ensure compliance with legislation and any other statutoryrequirements lies with the user. The user should adapt or supplement this document toensure compliance for the specific application.

Principal Changes from Previous Edition

Generally updated and re-formatted. Additional information included regardingfloating roof tanks.

Feedback and Further Information

Users are invited to feed back any comments and to detail experiences in theapplication of BP RPSE's, to assist in the process of their continuous improvement.

For feedback and further information, please contact Standards Group, BPInternational or the Custodian. See Quarterly Status List for contacts.


EARTHING AND BONDINGPAGE 1

1. INTRODUCTION

1.1 Scope

BP Group RP 12 series specify BP general requirements for electricalsystems, equipment, materials and installations.

This document (BP Group RP 12-16) specifies requirements forearthing and bonding of electrical and non-electrical equipment on bothland-based and offshore installations. It covers earthing of electricalequipment, earthing for the control of static electricity, earthing forprotection against lightning, earthing of tanks, and in certaincircumstances the measures necessary to protect against 'stray' currents.

The section dealing with protection against static electricity does notcover all the additional precautions which have to be observed whenhandling the range of products found in the petrochemical and relatedindustries. 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 controlsystems are covered in BP Group RP 30-1.

BP Group RP 30-1 should also be consulted for special requirements forapplications including intrinsically safe systems and electronic systems such ascomputers.

1.2 Quality Assurance

Verification of the vendor's quality system is normally part of the pre-qualificationprocedure, and is therefore not specified in the core text of this specification. Ifthis is not the case, clauses should be inserted to require the vendor to operate andbe prepared to demonstrate the quality system to the purchaser. The quality systemshould ensure that the technical and QA requirements specified in the enquiry andpurchase documents are applied to all materials, equipment and services providedby 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 beenreferenced in this document, their use does not preclude the application ofequivalent national Standards where these are available.

2. EARTHING OF ELECTRICAL CIRCUITS AND EQUIPMENT

2.1 General Requirements

2.1.1 In this document it is assumed that the power system has a neutralpoint at its source which is earthed directly or via a current limiting



device. However, regardless of the method of earthing the supply, oreven if the supply is not earthed, the same basic requirements forbonding will apply. For guidance on methods of earthing powersystems refer to BP Group RP 12-3.

2.1.2 Onshore power earthing systems shall be designed and installed asrecommended in BS 7430.

Section 4 paragraph 26 of BS 7430 mentions earthing in hazardous areas, howeverthe following should also be noted:-

The minimum earth fault current required to trip the circuit follows from thetripping characteristic of the overcurrent protective device being used. In view ofthe fact that earth fault currents may be passing through areas classified ashazardous, along unknown routes, it is appropriate to limit strictly the time forwhich such a fault condition could persist as well as seeking to ensure the safety ofthe electrical system.

Where electrical equipment is bonded to the main plant structure or directlyconnected to the common static and lightning earthing system, there will be manyearth paths in parallel with the cable armour and the required disconnection timecan normally be achieved.

In other circumstances however, the earth fault current return path may be via thecable armour alone. If the cable length exceeds that which will give the requiredlow value of earth loop impedance to trip the circuit within 5 seconds, specialmeasures may need to be taken to reduce the earth loop impedance. In the case ofa single cable, these measures may involve either increasing the cable size orproviding a separate earth return conductor in addition to the cable armouring. Inthe case of multiple cables, each circuit should be checked to ensure that the earthloop impedance for each circuit, taking account of all cable armourings in parallel,is low enough to pass the required earth fault current.

2.1.3 Typical earthing and bonding installations for both onshore andoffshore are shown in Fig. 1A, 1B, 2A and 2B.

The use of structural steelwork as part of an earthing current system and as a pathfor fault current is acceptable practice, particularly offshore where the welded steelstructure of the platform is regarded as 'earth'. The term only applies to verysubstantial permanent structures such as an offshore platform or an onshoreprocess plant.

When a complex structure is used as (one of) the protective conductors, itsimpedance cannot be readily calculated. However, it can be assumed that a verylarge structure such as an offshore platform has negligible impedance comparedwith that of the cable armouring. For the purpose of calculations, the impedanceof 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 bemaintained when extensions to the plant are designed.

2.1.4 Protective conductors may consist of one or a parallel combination ofthe following:



(i) Cable armouring or metallic sheath(ii) Rigid screwed conduit(iii) Earth core within a multicore cable(iv) Separate conductor(v) Structural steelwork

Sole reliance on cable armouring and/or metallic sheathing shall only bemade if it is adequately fault rated as a protective conductor.

Note Structural steelwork may be considered as a protectiveconductor provided it is part of the common static and lightningearthing system and there is a permanent metallic path for faultcurrent via such steelwork and other earthing conductors backto the source of the power supply.

This is a fundamental requirement which should be met in the case of faults withinelectrical equipment. In the case of faults within the cable, it may not be possibleto have armour which is fully fault-rated, particularly if the armour is of the steelbraid type. However, the advantages of steel braid armour over steel wire armouron cables used offshore are considered to outweigh this possible disadvantage.

2.1.5 The cross sectional area of every protective conductor and bondingconnection between exposed and extraneous conductive parts shall besuch that they are capable of carrying the earth fault current, or anappropriate fraction of the total fault current, for the duration of thefault without damage to the conductor or associated insulation.

The required minimum cross sectional area may be determined by thefollowing formula:

Sp = a I t

k mm2

where,

Sp = Cross-section of protective conductor (mm)I = Total earth fault current through the

protective device (amperes)a = Fraction of the fault current in that part

of the earth return path.t = Operating time of the disconnecting device (seconds)

k = Factor dependent on the material of theconductor, the type of insulation, theassumed initial temperature and the maximumallowable temperature of the insulation

Notes:



(i) Where electrical apparatus is required to be bonded to anearthing system, e.g. to earthed structural steelwork or buriedearthing grid, any cable used for such purpose shall be sized onthe assumption that it may carry the total fault current, i.e.assume a = 1.

(ii) Where the 'protective conductor' consists mainly of a large steelstructure such as an offshore platform, or an extensive mesh ofinterconnected copper earthing conductors, the impedance ofthe earth return path may generally be ignored for the purposeof fault current calculation.

(iii) Values of k for typical types of protective conductor are givenin Table 1. For conditions and conductor types not covered byTable 1, reference should be made to IEE Regulations forElectrical Installations, 16th Edition Tables 54B to 54F.

The formula is based on IEE Regulations for Electrical Installations, 16th Edition.

2.1.6 As an alternative to the above method of calculation, the size of copperprotective conductors and associated bonding connections may beselected from Table 2.

Notes:

(i) Minimum size without mechanical protection shall be 4 mm2.

(ii) 2.5 mm2 protective conductors shall be multistranded, i.e.7/0.67.

(iii) In practice it may be desirable for any one project, to limit thenumber of sizes of protective/bonding conductors to makepurchasing more economical and/or to simplify design andinstallation.

2.1.7 Buried earthing conductors should normally be bare copper cable ortapes. However, if there is a likelihood of corrosion (for exampleparticularly acidic soil) an overall protective covering, e.g. green/yellowPVC, shall be provided.

2.1.8 Joints in protective conductors should be avoided. If this is notpossible, effective measures shall be taken to prevent inadvertentdisconnection, corrosion or other forms of deterioration at all suchjoints.



2.1.9 For terminating high voltage cables, the design of the cable gland ortermination shall incorporate a lug for bonding the cable armour toearth, or to the equipment enclosure.

2.1.10 Where a low-voltage cable enters a metallic enclosure, a bondingconnection between the gland and the enclosure is not required,providing there is no electrical discontinuity of the enclosure. Tappedentry holes are preferred, but where entry is through a clearance hole a'star' washer shall be fitted under the backnut to ensure good electricalcontact. Refer to Figure 3.

2.1.11 Where plastic enclosures are used, means shall be provided to preservethe electrical continuity of the armouring and/or metallic sheaths ofcables. Refer to Figure 3.

2.2 Sub-stations

2.2.1 A bar of high conductivity hard drawn (hchd) copper shall be fixed tothe inside wall of the substation, to which the earth bars of allswitchboards and the metallic enclosures of all low-voltage ancillaryequipment (e.g. battery charger, lighting distribution board, etc.) shallbe connected. The minimum size of the copper conductor shall be 75mm2.

The main substation earth bar shall be connected to one or moreearthing busbars to form a complete ring. The earthing busbar(s) shallbe as shown in Figure 5.

Alternatively, stranded copper cable may be used to connect each itemto the earthing busbars. A typical earthing layout is shown in Fig. 1A.

2.2.2 The star points of all Dy and similarly connected transformers and allalternator windings shall be connected to the earthing system (eitherdirectly via a current limiting impedance and/or earthing switchgear, asrequired by BP Group RP 12-3). Either hard-drawn high-conductivitycopper bar or stranded copper cable shall be used and in either case theconductor shall have a green/yellow PVC covering. Figure 1A refersto this clause.

2.2.3 The neutral of low-voltage three phase four wire systems shall beconnected to earth via the relevant main switchboard earth bar. Abolted 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 tothis clause.

2.2.4 The tank of each main transformer shall be connected directly to anearthing bus-bar. Figure 1A refers to this clause.



2.2.5 The armouring and metallic sheath (if provided) of all multicore cablesshall, be bonded to the switchboard earth bar, via the termination or thegland and gland plate as detailed in BP Group GS 112-8 and GS 112-9.Figure 1A refers to this clause.

2.2.6 Where armours and/or metallic sheaths are specified on single corecables they shall be bonded to earth at each termination unless theassociated cable de-rating is unacceptable. A metallic gland platenormally provides an adequate bonding connection between thearmours but care must be taken to eliminate magnetic and eddy currenteffects if metal gland plates are used for single core cables.

In single core cable installations the effect of load current in the cable causesmagnetic fields between the conductors. Where the cable penetrates a ferrousmaterial the magnetic field interacts to produce hysteresis so that eddy currenteffects which will heat up the gland plate and can lead to insulation stress. Theeffect can be reduced by introducing an air gap (or other means of producing highmagnetic reluctance) between the cables and the eddy currents cannot flowconcentrically around the cable penetration. Alternately a non ferrous gland platecould be employed. In the latter case either corrosion due to dissimilar metalsneeds to be considered or the method of achieving the cable sheath earth bondneeds to be carefully considered.

The problems associated with eddy currents and hysteresis in single core cablesalso affect the armour should these be ferrous. Single core cables should alwayshave a non ferrous armour applied.

Where single point bonding is necessary unearthed termination's shallbe insulated and shrouded for the maximum possible touch voltage forthe application. The earthed end should be at the hazardous area end(if any). Maximum permissible sheath voltages to earth are 25V atsealing ends and 50V at joint positions. The maximum permissiblesubstation potential rise is 430V on systems protected by overcurrentprotection and 650V on systems with high speed protection. Figure 1Aand Figure 2A refers to this clause.

By limiting the sheath voltage to 50 v the system safety is enhanced by complyingwith the provisions of a functional extra low voltage system as defined in the IEERegulations for Electrical Installations 16th Edition.

Many standards offer levels to limit the rise of earth potentials during faultconditions, the levels referenced above have been adopted as good practice bybeing proven safe in addition to being readily achievable.

2.2.7 For onshore sites, electrodes shall be installed in the ground in thevicinity of each main substation. Connections to the electrodes androds shall be made using conductors of 70 mm2 minimum cross-sectional area.

The earth electrodes are used in this case to create a reference point for the supplysystem. They are not generally required to carry full fault currents as all electricalsupplies entering and emanating from the substation will have earth continuity



provided (i.e. by armours and separate earth conductors). Although it is thereforeless important to achieve a low electrode to earth resistance, the number andlength of the earth rods shall be such as to achieve a combined electrode resistanceto earth of 4 ohms or less under all soil conditions likely to occur. Figure 1A refersto this clause.

2.2.8 At least one more than the required minimum number of electrodesshall be installed. By this means, each electrode can be disconnectedone at a time for testing without affecting the integrity of the powerearthing system.

2.2.9 All main switchboards shall be connected to the substation earthingsystem at two separate points. Figure 1A refers to this clause.

2.3 High-voltage Motors

2.3.1 The enclosures of all high-voltage motors shall be connected directly tothe local static and lightning earthing system, or to local earthelectrodes. A common earth electrode system may be used for severalmotors in the same area. If high-voltage motors are already inpermanent electrical contact with steelwork forming part of thecommon earthing system, no additional copper bonding connections arerequired. Figure 1A refers to this clause.

2.3.2 Metallic enclosures of the local control station and any other associatedelectrical devices local to the motor, shall be bonded to the motorenclosure or to the earthing system to which the motor is connected.This may be achieved through the mounting bolts and earthedsteelwork. Figure 1A refers to this clause.

2.4 Low-voltage Equipment

2.4.1 If the enclosure is in permanent direct metallic contact, e.g. via pumpbedplates, vessels, piping, structures, etc., with the general mass ofearthed plant steelwork, there is no necessity for any further connectionto any earthing system. Figure 1A refers to this clause.

2.4.2 If the enclosure is not in permanent direct metallic contact with earthedplant steelwork or pipework, it shall be bonded to the static andlightning earthing systems or to the adjacent earthed steelwork bymeans of a copper conductor. Figure 1A refers to this clause.

2.5 Offshore Installations

2.5.1 Earthing shall comply generally with the IEE Regulations for theElectrical and Electronic Equipment of Mobile and Fixed OffshoreInstallations, Section 2.



2.5.2 The enclosure of each main generator, transformer and switchboardshall be solidly bonded to the steel structure. Figure 2A refers to thisclause.

2.5.3 The requirements of sections 2.1, 2.3 and 2.4 of this RecommendedPractice are also applicable, but the provisions of Figure 2A apply.

2.5.4 The position of all earthing connections shall be visible and easilyaccessible. Earthing points shall be protected against corrosion.

2.5.5 Where additional bonding connections are required, they shall be madeat welded bosses local to the equipment to avoid the need for longruns.

2.5.6 Providing that low-voltage electrical equipment is in permanent metalliccontact with the general mass of earthed steelwork, no further bondingconnection is required. If the protection arrangements are inaccordance with Table 3.

3. LIGHTNING AND STATIC EARTHING

3.1 General Requirements

3.1.1 The static earthing and bonding system shall be in accordance with therecommendations of BS 5958 or the equivalent national standard of thecountry of installation and shall be designed to take the maximumadvantage of inherent earthing. The minimum amount of copper tapeor conductor shall be used. In areas classified as hazardous, therelevant parts of BS 5345 or the equivalent national standard of thecountry of installation shall also be adhered to.

3.1.2 All equipment and parts of equipment which are liable to accumulatepotentially dangerous levels of static shall be in effective metalliccontact with adjacent metal and with 'earth'.

3.1.3 The resistance to earth from all parts of fixed metal equipment shall notexceed 10 ohms.

To prevent accumulation of static electricity, the resistance to earth may safely beas high as 108 ohms. For adequate discharge of lightning, resistances of 10 ohmsor less are required. Hence for general bonding a figure of 10 ohms should beadopted in order to satisfy both lightning and static requirements.

3.1.4 Normal pipe and equipment flanges, unless specially insulated, providea sufficiently low resistance to dissipate static electricity and do notrequire bonding connections across them. Similarly, any equipment



which is in metallic contact with an earthed metal structure does notrequire any other earthing connection.

Note: Earthing of fixed plant does not in all cases remove the risk ofstatic discharge. Other precautions are also necessary such asconnecting an earthing clamp to road tankers before filling,control of pumping rates, avoidance of splash filling, etc. Theseprecautions will typically be detailed in any relevant safetycodes that are applied.

The detailed design of lightning protection systems should generally bein accordance with BS 6651 or the equivalent national standard of thecountry of installation.

Guidance is given in BS 6651 on how the requirement for lightning protection forvarious structures can be assessed.

3.1.5 In order to protect against a direct lightning stroke, as a minimum, thetallest structure on the plant shall be directly earthed as close to thebase as possible with a minimum of two electrodes and the individualresistance of each shall not exceed 10 ohms.

3.1.6 Directly earthed items shall, where possible, also be connected to thegeneral earthing system.

3.1.7 Structures which are made of metal and which are electricallycontinuous do not require a separate down conductor for lightningprotection; a connection to earth at a point near the base is sufficient.

3.2 Common Earthing System

3.2.1 The requirements for protection against static electricity and lightningshall normally be met by a common earthing system to which allstructures and items of process equipment are connected either directlyor indirectly.

3.2.2 The common earthing system shall comprise either of, or a combinationof, the following elements:

(a) Buried 70 mm2 copper strip or single core copper conductor.

(b) A steel structure to which all equipment to be earthed is indirect contact or is bonded.

At onshore sites, the earthing system shall be independently connectedto a number of earth electrodes (minimum of 2). Figure 4 refers to thisclause.



3.2.3 Where the plant is located in proximity to the process area substation,the static and lightning earthing system shall be connected to the powerearthing system at two points.

3.3 Steel Structures (Onshore)

3.3.1 An earth lug or boss shall be welded to the main columns atapproximately 450 mm above ground level and at intervals of not morethan 30 m.

3.3.2 Where a steel structure forms the common earthing system, or partthereof, or requires direct earthing for lightning, each earth lug or bossshall be directly connected by 50 mm copper conductor tape to anadjacent earth electrode.

3.3.3 Where the steel structure does not form part of the common earthingsystem and does not require direct earthing for lightning, each lug orboss shall be connected by 35 mm copper conductor to the commonearthing system. Figure 4 refers to this clause.

3.4 Vessels and Storage Tanks

3.4.1 Vessels

3.4.1.1 When mounted directly on and in metallic contact with an earthed steelstructure, no further bonding is necessary other than that which may benecessary for lightning protection.

3.4.1.2 When the mounting is insulated from steelwork by materials havingpoor conductivity such as wood, concrete, rubber etc., two earthingconnections shall be taken from the vessel to the common earthingsystem. Where the vessel is so remote from the plant as to makeconnection to the common earthing system impractical, twoconnections shall be taken from the vessel to separate earth electrodesand the resistance to earth of each electrode shall not exceed 10 ohms.Figure 4 refers to this clause.

3.4.1.3 Looping of earthing conductors between vessels is permitted provideda connection is taken from each end of the 'looped' system to thegeneral earth system or earth electrodes.

3.4.1.4 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 10ohms is not achieved, additional earthing is required.



3.4.1.5 Earthing connections shall be 35 mm2 copper conductor except fordirect earthing connections for lightning which shall be 50 mm2 copperconductor.

3.4.1.6 Where a vessel has insulation and an outer metal cladding or wirereinforcement, the metal cladding or reinforcement shall be electricallycontinuous and bonded to the vessel. Figure 4 refers to this clause.

3.4.1.7 The armouring of cables which enter the vessel shall be bonded to theshell at the point of entry.

3.4.2 Storage Tanks

3.4.2.1 Tanks up to 30 m diameter shall be provided with two, and tanks over30 m diameter shall be provided with three, equally spaced earthingbosses. The bosses shall be positioned near the base of the tank and bein accordance with Figure 1A.

3.4.2.2 The earthing lugs or bosses on the tank shall be connected to the samenumber of separate earth electrodes as there are lugs or bosses, eitherindividually or on a shared basis. The earth electrodes should preferablybe close to the tank base.

3.4.2.3 For a group of tanks, earth electrodes common to the group may beinstalled provided that each tank has, as a minimum, two paths to earth.This ensures that during testing of one electrode, the tank will remainearthed by a system with an earth resistance not exceeding 10 ohms.

3.4.2.4 All tank internals, e.g. mixers, gauge floats and sling arms, shall bebonded to the tank shell at one or more locations depending on the sizeof the internal object.

Bonding can preferably be achieved by direct bolting. Care should be taken toavoid the formation of re-entrant loops.

3.4.2.5 On floating roof tanks, multiple shunt connections comprising stainlesssteel strips 50 x 0.6 x 400 mm long, shall be provided between thefloating roof and the tubbing shoe at adequate intervals around the roofperiphery or one per pantograph where these are fitted.

Where high winds prevail the shunt strips may be replaced with cablesbolted in position. Shunts should be fitted above the sealingarrangement.

The spacing of shunt connections should avoid the risk of dischargefrom the roof to the tank wall directly across the gap rather than via ashunt, due to the formation of re-entrant loops. BS 6651 givesguidance that the risk is increased when the path length of the loopexceeds eight time the width of the open side. In this case the



maximum loop length is half the peripheral distance of the closed pathbetween adjacent shunts.

Although hanger linkages on the pantograph offer an earthing path from thefloating roof to the shell they can be a source of arcs during a lightning strike ifplaced too close together (accepted minimum on an empirical basis is 1 m). Thearcs occur from sharp points or joints. The arcs may be avoided by installation of ashort insulated jumper around each pinned hanger joint together with coveringsharp points of hangers with insulating material.

3.4.2.6 When a rolling ladder is fitted, a 35 mm2 flexible copper bondingconductor shall be applied across the ladder hinges, between the ladderand the tank top, and between the ladder and the floating roof. (This isin addition to earthing required in 3.4.2.5)

The earthing provisions assume the ladder is articulated in the centre in a mannerwhich allows continuity of earthing. Where there may be appreciable movement ofthe ladder at either the roof or rim which makes earth bonding non feasible,another approach entirely may be necessary. No specific advice is available forthis eventuality but past instances have led to arrangements which stowed laddersaway from the roof when not in use.

3.4.2.7 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 tankshell was practised as a supplement to the pantograph earthing system. However,experience showed that these cables frequently became entangled and broke withthe movement of the roof. Also, the tangling of the cable produced re-entrant loops.Thus, this practice is no longer recommended.

3.4.2.8 As an alternative to the provisions of 3.4.2.7 lightning protection canbe achieved using an air termination network as described in clause21.2 of BS 6651.

3.4.3 Floating Roof Tanks without Rolling Ladders

3.4.3.1 Figures 6 - 11 give suggested typical details for earthing floating rooftanks when no rolling ladder is fitted.

3.4.3.2 Earthing of the roof should be provided by 70 mm2 flexible earth cables(e.g. neoprene covered) laid along the roof drain.

3.4.3.3 One earth cable should be installed for each roof drain. Typicalschemes are shown in Figures 6, 7 and 9.



3.4.3.4 Suggested Roof connections for double and single roof tanks areshown in Figures 8 and 10. The connections should be to a similarmaterial specification to that for the tank itself.

3.4.3.5 Roof connections should be sited close to the roof drains with suitablefacilities to securely fix the earth cable to the roof. All connectionsshould be protected against corrosion.

3.4.3.6 At the point where the earth cable exits the roof connection adetensioner (see Figure 11) should be fitted. The earth cable shouldthen be fixed to the roof drain using suitable clips (e.g. stainless steelcable ties) with due allowance for movement of all swivels.

3.4.3.7 Once earthing cables have been installed, tests should be undertaken toensure there is a low resistance (less than 0.1 ohm) between the roofand the wall.

3.5 Metallic Stacks and Towers (Not applicable to Flare Stacks)

3.5.1 Provided they are of welded, bolted or riveted construction, no airterminals or down conductors are required. Figure 4 refers to thisclause.

3.5.2 Two earth lugs or bosses near to the ground, on opposite sides of theequipment, shall be provided and independently connected either to thegeneral earthing system or to two earth electrodes near to the base ofthe equipment. The method used shall depend on the need forprotection against direct lightning strokes.

3.5.3 The armouring of all cables which enter metallic stacks shall be bondedto the stack at the point of entry. Figure 4 refers to this clause.

3.6 Non-metallic Structures

3.6.1 In all areas classified as hazardous, steelwork such as stairways, cableracks, handrails, etc., which is mounted on or attached to non-metallicstructures shall be bonded to the general earthing system either directlyor via other earthed metal at intervals not exceeding 30 m.

If such steelwork is not already bonded as an extraneous conductivepart (IEE wiring regulations) then as an alternative to bonding, anassessment shall be carried out to ensure:-

(a) that the steelwork is sufficiently isolated from other potentiallightning discharge carrying conductors to ensure no sideflashing will occur, guidance is given in BS 6651.



(b) no static build up above the minimum ignition energy ofhydrocarbons present is possible, guidance given in BS 5958Part 1.

3.6.2 Non-metallic structures less than 9 m in height do not generally requirelightning protection or earthing. If greater than 18 m in height, theyshall be provided with lightning protection. Figure 4 refers to thisclause.

3.6.3 The need for lightning protection on non-metallic structures between 9m and 18 m in height shall be determined taking into account theheights of other adjacent structures, the nearness of flammablematerials, consequences of damage, etc. BS 6651 or the equivalentnational standard of the country of installation should be referred to forguidance.

3.7 Metallic Guy Ropes

3.7.1 Metallic guy ropes used for supporting metallic or non-metallic stacksor other structures shall be bonded at their upper ends to the stack orstructure if metallic, or to the lightning protective system in the case ofnon-metallic stacks or structures. The lower end of each guy rope shallbe directly earthed. Where a guy rope is comprised of two ropes inparallel, they shall be bonded together at the upper and lower ends andthen treated as one rope. Figure 4 refers to this clause.

3.8 Pipelines and Valves

3.8.1 It is not necessary to bond across the flanges of pipe joints, nor is itnormally necessary to earth pipelines separately, since adequateearthing is provided via the vessels and other equipment to which thepipes are connected. However, long pipelines crossing open groundshall be earthed at or near any plant boundary. The spindles of all ballvalves will need to be bonded to their pipeline only where the ball valveis controlling a two phase mixture, and where the valve is not fittedwith a special earthing washer, or where the valve is immediatelydownstream of fine filtration facilities.

Charge generation is increased in a two phase mixture due to theincreased surface area of the individual phases, and is increaseddownstream of fine filters due to extensive charge separation.

3.8.2 An exception to 3.8.1 shall be made in areas where liquefied petroleumgas is handled such as tanker loading bays. Particular attention shouldbe paid to earthing across flexible connections.

As LPG is normally contained in closed systems there is no dangerunder these conditions as the gas concentration will be well above the



upper flammable limit. The release and/or rapid expansion of LPGresults in the formation of a mist which is capable of generating staticelectricity. Danger only exists therefore where LPG is handled, andthere is the risk of static build up if all metallic parts are not adequatelybonded.

3.8.3 For earthing associated with cathodically protected pipelines, referenceshould be made to Section 6 of this Recommended Practice.

3.9 Machine Sets with Non-electric Drive

3.9.1 When driving and driven machines are in direct metallic contact with anearthed steel structure, no further earthing is required.

3.9.2 When the driving and driven machines are bolted to a common metallicbedplate which is on a concrete or other poorly conducting foundation,one connection shall be taken from the bedplate to the general earthingsystem. Figure 4 refers to this clause.

3.9.3 When the driving and driven machines are on separate bedplatesmounted on separate concrete plinths or other poorly conductingmaterial, the bedplates shall be bonded together and one connectionshall be taken to the general earthing system. Figure 4 refers to thisclause.

3.9.4 All earth connections shall be 35 mm2 copper conductor.

3.10 Machine Sets with Electric Drive

3.10.1 No specific earthing connection is required if the driven machine ismounted on a metallic bedplate providing for the dissipation of static.Figure 4 refers to this clause.

3.11 Road Tanker Loading Bays

3.11.1 Each loading gantry shall have a connection to earth at each end of thegantry. The connections may be direct to independent earth electrodesor to the general earthing system of adjacent plant. The individualresistance to earth of the connections to the earthing system shall notexceed 10 ohms.

3.11.2 All product pipelines shall be bonded to the loading gantry either bymeans of pipe clamps or pipe flange bolts.

3.11.3 All loading hoses shall be electrically continuous from the productpipeline to the loading nozzle or flange. A bond shall be installedacross each swivel joint in metallic loading arms.



3.11.4 Each loading bay shall be provided with a number of flexibleconnections of 35 mm2 copper which are bolted to an earth boss in theloading gantry at one end, and which have a robust earthing clamp ofan approved type for the other end for bonding the tanker to earthduring loading and discharge.

3.11.5 For LPG loading bays, the earthing arrangements for the vehicle shallensure that the earth connection shall be completed in an area classifiedas non hazardous or via an earthing switch in a suitably certifiedenclosure.

3.11.6 Earth proving devices and interlock arrangements shall be provided sothat tanker loading or discharge is possible only when effective earthinghas been achieved.

3.11.7 All connections to earth shall be 35 mm2 stranded copper conductor.

3.12 Rail Car Loading Bays

3.12.1 The requirements of 3.11 of this Recommended Practice apply, exceptthat a flexible cable connection is not required since the contactbetween the tanker wheels and the track provides sufficient earthing.

3.12.2 All rails shall be bonded together and connected to the loading gantryor earthing system.

3.12.3 To guard against stray currents, insulated joints shall be inserted in therails to isolate those in the loading gantry from the remainder of the railsystem.

3.12.4 On electrified rail systems the live contact rails or overhead conductorsshall terminate outside the loading compound.

3.13 Sea Tanker Loading Jetties

3.13.1 The earthing and bonding system on tanker loading jetties shall complygenerally with the International Safety Guide for Oil Tankers andTerminals.

3.13.2 The loading arms on all jetties shall have an insulated flange inserted inthe 'outboard' end of the loading arm to prevent flows of stray currentalong the loading arm and hence potential sparking when theconnection 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.



3.13.3 For jetties using hose loading gantries, the jib handling rig hook shall beinsulated.

3.13.4 Breasting dolphins, fenders and quays having metallic parts connectedto the jetty earthing system shall be protected from direct contact withships hulls, e.g. by wooden linings.

3.13.5 Mooring dolphins shall be insulated from the jetty earthing system orlocated in a safe area but insulated from the shore earthing system.

3.13.6 Insulating flanges shall be inserted in each pipeline at the shore end.The jetty structure and earthing system should also be isolated from theshore earthing system.

3.13.7 In the case of steel jetties which have impressed current cathodicprotection, cables entering the jetty area from the shore should havetheir metallic sheaths and/or armours bonded to the jetty earthingsystem but isolated from the shore earthing system at the shore end.Where this connection presents excessive diversion of impressedcurrent, resulting in the protection potential not being maintained, analternative insulation arrangement shall be utilised.

It is no longer considered safe practice to bond the tanker to the jetty earthingsystem, because of potential difference which may exist due to cathodic protectionof the ship's hull and/or the jetty structure. When such a bond is broken, anincendive spark can be produced. (See International Safety Guide for Oil Tankersand 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 amulti-meter, which should be of a type of protection suitable for the classificationof the area. See BP Group RP 12-2 for guidance.

3.14 Portable Container Filling

3.14.1 In addition to the earthing of items already mentioned in this section,the following shall be electrically continuous and bonded to thecommon earthing system or to an earthing system installed specificallyfor the filling installation:

(i) Weighing machine platforms and bases(ii) Conveyor tracks(iii) Any other ancillary equipment.

Filling hoses shall be electrically continuous. A separate flexibleearthing lead with a robust clip or clamp shall be provided forconnecting to the drum during filling, although such an arrangement isnot necessary for the filling of pressure containers.



An earth proving unit, interlocked with the product delivery pumpsshall be installed.

3.15 Offshore Installations

3.15.1 All plant which is not in metallic contact with earthed structuralsteelwork shall be bonded to the platform steelwork. A separateearthing system for lightning and static protection is not required.

3.15.2 A reel of single core flexible cable, minimum size 35 mm, shall beinstalled in an area classified as non-hazardous by the helideck, forbonding helicopters to the platform during refuelling. The reel shallincorporate a slip ring to pick up the connection to earth.

4. EARTHING SYSTEM DESIGN

4.1 Soil Resistivity

4.1.1 The resistance of an earth electrode of given dimensions and geometryis dependent on the soil resistivity, which varies according to the typeof soil, moisture content, degree of compaction and chemicalcomposition. Specific guidance on soil resistivities for various types ofsoil is given in BS 7430, Table 1.

4.1.2 Resistivity measurements shall be made at the proposed electrodelocations. These measurements and the subsequent electrode designshould be carried out at an early stage of the project so that theelectrode locations are compatible with plot layouts, foundations, etc.

4.1.3 Where there is any option, a site should be chosen for the electrodeswhich is not naturally well drained. However the ground need not bewater-logged. Locations where the ground is kept moist by waterflowing over it should be avoided. Wherever possible, dry, sandy orrocky ground should also be avoided.

4.1.4 The effect of possible seasonal increases in electrode resistance due todrying out or freezing of the ground shall be taken into account.Wherever possible, the earth electrode should be installed deep enoughto reach the water table or permanent moisture level, deeper than frostis likely to penetrate and to reach stable ground conditions.

4.1.5 Bentonite or similar material may be used to improve contact efficiencyin difficult ground conditions.



4.2 Earth Electrodes

4.2.1 Earth electrodes shall normally consist of a number of rod sectionscoupled together and driven vertically into the ground. A number ofsuch rods may need to be connected in parallel to obtain the requiredelectrode resistance. The distance between rods should be greater thantheir depth.

In soils of uniform resistivity, it is more economical to install a number of rodsconnected in parallel than to attempt to obtain the required resistance from asingle deeply driven rod. However if the rods are driven too closely together, theireffectiveness is reduced. In practice, a separation of less than 3m should beavoided.

4.2.2 Earthing materials shall comply generally with the requirements of BS6651 or the equivalent national standard of the country of installation.

4.2.3 Earth rods may be of the following materials providing that they areentirely suitable for the application and ground conditions:

(i) solid hard drawn copper(ii) phosphor bronze(iii) copper clad steel(iv) stainless steel(v) galvanised steel.(vi) 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 minimumdiameter shall be 15 mm.

4.2.4 Copper clad steel rods shall be of the molecularly bonded type. Thethickness of copper shall be 0.25 mm minimum and the coating shall bemaintained over the entire length of the rod including the threadedportion. Couplings shall be made of silicone aluminium bronze andshall be of sufficient length to enclose completely the threads with therods in end-to-end contact.

4.2.5 Each earth rod shall be protected against corrosion and terminated inan inspection pit complying with Figure 5.

5. EARTHING WHERE CATHODIC PROTECTION IS APPLIED

5.1 Cathodic protection system design shall comply generally with BS 7361Pt 1. Attention is drawn particularly to 12.3.1 and 12.4 of BS 7361 Pt1.



5.2 Bonding between a cathodically protected pipeline or storage tank,etc., and any earthing system can reduce the efficiency of an impressedcurrent cathodic protection system by diverting the flow of impressedcurrent. As far as possible, the cathodically protected sections ofpipeline should be isolated from unprotected sections and from anyearthing systems, although the presence in the line of electricallyoperated valves may make complete isolation impractical.

Isolation can be achieved when electrically operated valves or otherdevices are installed by inserting insulating bushes between the cablegland and the device. In this case the device should be bonded to thepipeline. It should be established however that a return earth path viathe pipeline is sufficient to ensure correct operation of protectivedevices on the supply to the equipment.

Sometimes it is necessary to earth buried pipelines which are impressedcurrent cathodically protected, e.g. to alleviate the effects of localoverhead power lines. In such cases the pipeline should be earthed bypolarisation cells or alternatively by the use of earthing rod materials ofa suitable galvanic potential.

5.3 Where plant is cathodically protected, either by sacrificial anodes or byan impressed current system, the design of the earthing systems shall beagreed with the suppliers and designers of the cathodic protectionsystem.



Material of Protective Conductor Assumed InitialTemperature °°C

FinalTemp.°°C

k

Copper with PVC sheath 30 160 143Bare copper 30 200 159Copper as a core of a PVC cable 70 160 115Copper as a core of an EPR cable 85 220 134Steel armour in contact with PVC 60 200 51Lead sheath in contact with PVC 60 200 26Bare steelwork 30 200 58

TABLE 1

Typical Values Of K For Protective Conductorsand Fault Rated BondingConnections (Based On The IEE Wiring Regulations)

Cross-sectional Areaof Associated CurrentCarrying Conductor

mm

Minimum Cross-sectionalArea of Copper

Earthing/Bonding Connectionmm

1.0 2.5 See Notes1.5 2.5 } In2.5 2.5 (i) & (ii) Para 2.1.64 46 610 1016 1625 1635 1650 2570 3595 50

120 and over 70

TABLE 2

Minimum Cross Sectional Area Of SeparateCopper Protective Conductors AndBonding Connections (Based On The IEE Wiring Regulations)



System Voltage Protection arrangements not requiring

supplementary bonding110V up to and

including440V

Protective device rating 32 A or less; or RCDprotected.

55-0-55 V Fuse rating 16 A or less; orMCB rating 32 A or less; orRCD protected.

24 V Fuse rating 6 A or less; orMCB rating 10 A or less; orRCD protected.

TABLE 3

Conditions for Which Supplementary Bonding is not Required

(Based on the IEE Recommendations for the Electrical and Electronic Equipment ofMobile and Fixed Offshore Installations)

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

23

NO

TE

S:

1.N

UM

BE

RS SH

OW

N T

HU

S 2.2.1 IND

ICA

TE

TH

E R

EL

EV

AN

T C

LA

USE

IN T

HE

TE

XT

.2.

FOR

EA

RT

HIN

G D

ET

AIL

S SEE

FIG 5.

FIG

UR

E 1A

Typical M

ethods of Earthing E

lectrical Equipm

ent Onshore



NOTES:

1. APPARATUS WHICH IS BONDED TO AN EARTHED STEEL STRUCTUREBY MEANS OF ITS HOLDING DOWN BOLTS OR BY WELDINGREQUIRES NO ADDITIONAL BONDING CONNECTION.

2. APPARATUS WHICH IS OTHERWISE ISOLATED FROM THE EARTHINGSYSTEM SHOULD BE BONDED AS SHOWN. THE CROSS SECTION OFTHE EARTH BOND SHOULD BE IN ACCORDANCE WITH SUB-SECTION2.1.5 OR 2.1.6.

3. WHERE THE PLANT/APPARATUS IS REMOTE FROM THE SUB-STATIONTHE EARTHING SYSTEMS NEED NOT BE INTERCONNECTED. IN THISCASE EARTH FAULT CURRENT WILL RETURN VIA THE CABLEARMOUR OR EARTH CORE. ACCOUNT SHOULD BE TAKEN OFPARALLEL EARTH PATHS VIA THE ARMOUR OF OTHER CABLES.

FIGURE 1B

Earthing Principles Onshore



FIGURE 2A( PAGE 1 OF 2 )

Typical Methods of Earthing Electrical Equipment Offshore



NOTES

1. FIXED OFF SHORE INSTALLATIONS ARE GROUNDED OR EARTHED INTO THESEABED 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 THESTRUCTURAL SUPPORT STEELWORK TO EXTEND THE EARTH CONTINUITYTO THE EXTREMEITIES OF THE INSTALLATION.

3. ALL TANKS, VESSELS,PIPE DUCT & TRAYWORK, HANDLING & ACCESSWAYS ARE BOLTED OR WELDED TO THE STRUCTURAL STEELWORK TOENSURE THAT ANY STATIC POTENTIAL BUILD UP WILL BE AVOIDED BYCONTINUOUS DRAIN TO ‘EARTH’

4. ALL LIVE CONDUCTORS ARE PROTECTED AGAINST TOUCHING BYPERSONNEL, CORROSION AND POSSIBLE MECHANICAL DAMAGE

5. ALL METALLIC ENCLOSURES, GLAND PLATES & CABLES GLANDS HAVEEARTH CONTINUITY BY PHYSICAL CONNECTION.

6. ALL INSULATED ENCLOSURES HAVE EARTH CONTINUITY FACILITY FORINTERNAL METAL WORK, VIA CABLE ARMOURING SYSTEM.

7. NEUTRALS OF LV SYSTEMS ARE EARTHED AT THE SWITCHBOARD8. EXPOSED METALLIC PARTS OF ELECTRICAL EQUIPMENT ARE IN

ELECTRICAL CONTACT WITH THE STRUCTURE BY HOLDING DOWN BOLTS,BEDPLATES ETC, BUT ADDTIONAL BONDING CONNECTIONS ARE REQUIREDWHERE INDICATED

9. NUMBERS SHOWN THUS :- 2.2.1 INDICATE THE RELAVENT CLAUSE IN THETEXT.

10. THIS DRAWING IS BASED ON FIG 2.1 OF THE IEE RECOMMENDATIONS FORTHE ELECTRICAL & ELECTRONIC EQUIPMENT OF MOBILE & FIXEDOFFSHORE INSTALLATIONS.

FIGURE 2A( PAGE 2 OF 2 )

Typical Methods of Earthing Electrical Equipment Offshore

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

27

FIG

UR

E 2B

( PA

GE

1 OF

2 )

Earthing P

rinciples Offshore



NOTES

1. THE STEEL STRUCTURE OF THE PLATFORM JACKET & MODULESFORMS THE EARTHING SYSTEM & THE PRINCIPLE PROTECTIVECONDUCTOR

2. EXPOSED METALLIC PARTS OF ELECTRICAL ( & NON ELECTRICAL )APPARATUS ARE NORMALLY EFFECTIVILY BONDED TO THE STEELSTRUCTURE BY HOLDING DOWN BOLTS, BEDPLATES WELDS ETCBUT ADDTIONAL BONDING CONNECTIONS ARE REQUIRED WHEREINDICATED

3. ALL TANKS, VESSELS . PIPES, DUCTS, TRAYWORK, HANDRAILS, ETC.ARE BOLTED OR WELDED TO THE STEEL STRUCTURE ENSURINGELECTRICAL 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 & THEARMOURING OF OTHER CABLES.

FIGURE 2B( PAGE 2 OF 2 )

EARTHING PRINCIPLES OFFSHORE



NOTES

1. WHERE CABLES ENTER A METALLIC ENCLOSURE IT IS NOT NECESSARY TOINSTALL ADDTIONAL BONDING CONNECTIONS BETWEEN GLANDS ORBETWEEN GLANDS AND THE EQUIPMENT, PROVIDED THAT THE ENTRY ISTAPPED OR A ‘ STAR ‘ WASHER IS FITTED UNDER THE BACKNUT TOENSURE GOOD ELECTRICITY

2. WHERE CABLES ENTER A NON-METALLIC ENCLOSURE MEANS SHOULD BEPROVIDED EITHER INTERNALLY OR EXTERNALLY FOR BONDING THECABLE ARMOUR TO EACH OTHER & TO EARTH. ( THIS IS NORMALLYACHIEVED WITH AN EARTH CONTINUITY PLATE INTERNALLY ON THEENCLOSURE ).

FIGURE 3

Bonding Principles Cable Glands

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

30

NO

TE

S1. N

UM

BE

RS SH

OW

N T

HU

S 3.4.1 RE

FER

TO

TH

E R

EL

AV

EN

T C

LA

USE

OF T

HE

TE

XT

2. FOR

EA

RT

HIN

G D

ET

AIL

S RE

FER

FIG 5

3. TH

IS D

IAG

RA

M

IS IN

TE

ND

ED

T

O

ILL

UST

RA

TE

A

T

YPIC

AL

ST

AT

IC

AN

D

LIG

HT

ING

EA

RT

HIN

G SC

HE

ME

. IN PR

AC

TIC

E T

HE

DE

SIGN

OF T

HE

EA

RT

HIN

G SY

STE

M W

ILL

DE

PEN

DO

N

SITE

C

ON

DIT

ION

S, SO

IL

RE

SISTIV

ITY

, PL

AN

T

LA

YO

UT

, N

EE

D

FOR

L

IGH

TIN

GPR

OT

EC

TIO

N,E

TC



FIGURE 4

Static and Lightning Earthing Systems (Onshore) General Principles

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

32

FIG

UR

E 5 ( P

AG

E 1 O

F 2 )

Typical E

arth Rod and E

arth Bar D

etails



NOTES

1. CONDUCTORS MINIMUM SIZE & TYPE OR EARTH CONDUCTOR FORGENERAL USE SHALL BE 25 x 3 COPPER TAPE OR 70mm2 BARE COPPERCABLE MINIMUM SIZE & TYPE OF FLEXIBLE EARTH CONDUCTOR SHOULDBE 35mm2 276/0 SINGLE CORE 600/1000 VOLT GRADE. WHILST COPPERCONDUCTORS ARE PREFERRED OTHER EQUVALANT MATERIALS MAY BEUSED SUBJECT TO APPROVAL FOR MECHANICAL PROTECTION OR WHERECORROSIVE CONDITIONS MAY EXIST AN OVERALL COVERING, eg PVC,SHALL BE PROVIDED

2. WHERE RODS CANNOT BE DRIVEN TO A SUITABLE DEPTH THEIRINSTALLATION MUST BE PRECEDED BY DRILLING. CARE MUST BE TAKENTO ENSURE THE SATISFACTIRY CONSOLIDATION OF THE BACKFILL SOILRESISTIVITY CAN BE REDUCED BY THE USE OF A SUITABLE SOILCONDITIONING AGENT. SALT B AGENT SHOULD BE AVOIDED AS THEYENCOURGE CORROSION.

3. THE USE OF CLADWELD JOINTING TECHNIQUE IS PERMITTED FOR THEEARTH CONDUCTOR JOINTS, AND IS THE PREFERRED METHOD FORUNDERGROUND JOINTS.

5. EARTHING BOSSES WELDED TO PRESURISED VESSELS SHALL BE OF THESAME MATERIAL QUALITY AS THE VESSEL

FIGURE 5 ( PAGE 2 OF 2 )

Typical Earth Rod and Earth Bar Details

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

34

FIG

UR

E 6

Typical C

onnections for Double R

oof Tank w

ith 4" Outlet

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

35

FIG

UR

E 7

Typical C

onnections for Double R

oof Tank w

ith 6" Outlet



FIGURE 8

Typical Roof Connection for Double Roof Tank

RP

12-16E

LE

CT

RIC

AL

SYST

EM

S AN

D IN

STA

LL

AT

ION

SE

AR

TH

ING

AN

D B

ON

DIN

GPA

GE

37

FIG

UR

E 9

Typical C

onnections for Single Roof T

ank



FIGURE 10

Typical Roof Connection for Single Roof Tank



FIGURE 11

Typical Cable Detensioner



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.

Note: Two metallic parts which are welded or solidly bolted togetherso as to form a permanent conductive path across thejoint or through the bolts may be considered to be'bonded'.

bonding: particular attention shall be given to the potential for deterioration ofbolted connections due to corrosion. Most welding techniques and boltedlugs are usually found to be entirely satisfactory.

exposed conductive parts: a conductive part of electrical equipment which can be touchedand which is not live but may become live under faultconditions.

extraneous conductive parts: exposed metal parts of other services or of a structure whichare normally at earth potential.

high voltage: a system whose voltage exceeds 1000 V a.c. or 1500 d.c.between conductors.

low voltage: a system whose voltage does not exceed 1000 V a.c. or 1500 Vd.c. between conductors.

protective conductor: a conductor connecting exposed or extraneous conductive partsto the earthed point of the source, to provide a return path forfault current.

Abbreviations

BS British StandardEN European StandardIEC International Electrotechnical CommissionIEE Institution of Electrical EngineersIP Institute of PetroleumISO International Standards OrganisationPVC Polyvinyl ChlorideSI Systeme International d'Unites



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 orotherwise recognised provided that it can be shown to the satisfaction of the purchaser'sprofessional 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 CompaniesInternational Marine Forum/International Association of Portsand Harbours)

British Codes and Standards

BS 5345 Code of practice for the selection, installation and maintenanceof electrical apparatus for use in potentially explosiveatmospheres (other than mining applications or explosiveprocessing and manufacture).

BS 5958 Code of Practice for the control of undesirable static electricity.

BS 6651 Protection of structures against lightning.

BS 7361 Pt 1 Cathodic protection part 1. Code of practice for land andmarine applications. (Formerly CP 1021)

BS 7430 Code of Practice for Earthing (Formerly CP 1013 : 1965)

UK Industry Standards

IP Institute of Petroleum Model Code of Safe Practice: Part 1Electrical.

IEE Regulations for Electrical Installations (Wiring Regulations).16th Edition.

IEE Recommendations for the Electrical and Electronic Equipmentof Mobile and Fixed Offshore Installations.



BP Group Documents

BP Group RP 12-2 Electrical Equipment in Flammable Atmospheres andCombustible Dusts(replaces BP CP 17 Part 1)

BP Group RP 12-3 Power System Design(replaces BP CP 17 Part 3)

BP Group RP 30-1 Instrumentation(replaces BP CP 18 Part 2)

BP Group RP 58-1 Petroleum and Petrochemical Storage(replaces BP CP 21)

BP Group GS 112-9 High-voltage Switchgear and Control Gear(replaces BP Std 225)

BP Group GS 112-8 Low-voltage Switchgear and Control Gear(replaces BP Std 227)