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Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’semployees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,or disclosed to third parties, or otherwise used in whole, or in part,without the written permission of the Vice President, EngineeringServices, Saudi Aramco.

Chapter : Electrical For additional information on this subject, contactFile Reference: EEX20502 W.A. Roussel on 874-1320

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Design And ApplicationOf Equipment Grounding

Engineering Encyclopedia Electrical

Design and Application of Equipment Grounding

Saudi Aramco DeskTop Standards

CONTENTS PAGES

Locating Equipment Grounding Information...............................................................1

Basis For Installing Equipment Grounds In Saudi Aramco ElectricalSystems .....................................................................................................................6

Determining The Equipment Grounding Requirements For SaudiAramco Electrical Systems ......................................................................................15

Determining The Stationary Equipment Grounding Requirement ForSaudi Aramco Electrical Installations.......................................................................27

Determining The Mobile Equipment Grounding Requirements ForSaudi Aramco Electrical Installations.......................................................................38

Determining The Building And Structure Grounding Requirements ForSaudi Aramco Installations ......................................................................................42

Determining The Lightning Protection Requirements For SaudiAramco Installations.................................................................................................44

Determining The Static Grounding Requirements For Saudi AramcoInstallations ..............................................................................................................54

Determining The Grounding Requirements For Saudi AramcoOffshore Platforms ...................................................................................................62

Determining The Grounding Requirements For Digital EquipmentUsed At Saudi Aramco Installations.........................................................................64

Work Aid 1: Saudi Aramco And Industry Standards Applicable ToEquipment Grounding ..........................................................................67

Work Aid 2: Formula And Table Of Wire Sizes And Ampacity ................................68

Work Aid 3: Formula To Determine Conductor Size And ReferencesFor Determining Stationary Equipment GroundingRequirements.......................................................................................74



Saudi Aramco DeskTop Standards

Work Aid 4: Formula To Determine Conductor Size And ReferencesFor Determining Mobile Equipment GroundingRequirements.......................................................................................75

Work Aid 5: References For Determining Building And StructureGrounding Requirements.....................................................................76

Work Aid 6: References For Determining Lightning ProtectionRequirements And Tables For Calculating Risk Index ........................77

Work Aid 7: References For Determining Static GroundingRequirements.......................................................................................80

Work Aid 8: References For Determining Offshore Platform GroundingRequirements.......................................................................................81

Work Aid 9: References For Determining Digital Equipment GroundingRequirements.......................................................................................82

Glossary...................................................................................................................83

Addendum A ............................................................................................................87



Saudi Aramco DeskTop Standards 1

LOCATING EQUIPMENT GROUNDING INFORMATION

The Engineer should consult the following Saudi Aramco Standards and Industry Standardsfor answers to questions on locating equipment grounding information:

_ Saudi Aramco Design Practices_ Saudi Aramco Engineering Standards_ IEEE Standards_ National Electrical Code

Saudi Aramco Design Practices

The Saudi Aramco Design Practice, SADP-P-111, applies to the design and the application ofequipment grounding for Saudi Aramco electrical installations. The following chapters ofSADP-P-111 contain information on equipment grounding:

_ Chapter 6_ Chapter 8_ Chapter 9_ Chapter 12_ Chapter 13

Chapter 6

Chapter 6 of SADP-P-111, titled "Equipment Grounding," discusses the specific SaudiAramco requirements for the grounding of the metallic parts of equipment that does notnormally carry current. The following specific topics are discussed in Chapter 6:

_ General Requirements_ Generators and Motors_ Switchboards_ Transmission Substations_ Transmission Lines_ Overhead Distribution_ Industrial Plant Areas_ Distribution and Utilization - 600 V and Below_ Cable Sheaths_ Fences_ Instruments, Meters, Relays, Instrument Transformers_ Cable Trays_ Conduits




Saudi Aramco Design Practices (Cont'd)

_ Cranes and Mechanical Handling Equipment_ Computer Installations_ Portable Equipment_ Lightning Protection

Chapter 8

Chapter 8 of SADP-P-111, titled "Offshore Platforms," discusses the specific groundingpractices for use on Saudi Aramco offshore platforms. The following specific topics arediscussed in Chapter 8:

_ General Requirements_ Grounding Electrode_ Grounding Conductors_ Installation

Chapter 9

Chapter 9 of SADP-P-111, titled "Lightning Protection of Buildings and Structures,"discusses the general lightning protection requirements for Saudi Aramco buildings andstructures such as flag poles and floodlighting poles. Chapter 9 does not apply to thelightning protection requirements in substations or to the problems associated with flammableliquids or gases. The following specific topics are discussed in Chapter 9:

_ General Requirements_ Need for Protection_ Materials_ Component Parts of a Lightning Protection System

Chapter 12

Chapter 12 of SADP-P-111, titled "Communication Facility Grounding," discusses the designcriteria for the grounding and the bonding of communication facilities. The followingspecific topics are discussed in Chapter 12:

_ General Requirements_ Terminology_ Design Criteria_ Earth Resistance and Bonding Requirements_ Review and Adoption of GTE Practices




Saudi Aramco Design Practices (Cont'd)

Chapter 13

Chapter 13 of SADP-P-111, titled "Safeguards Against Static Electricity, Lightning, and StrayCurrents," describes current Saudi Aramco practices and requirements to safeguard againstpossible ignitions from static electricity, lightning, and stray currents when a hazard exists inthe handling of flammable materials.

Chapter 13 is intended to supplement but not to replace Article 250 (Grounding) of theNational Electrical Code (NFPA 70), which deals with the protection of electrical installationsby grounding or bonding.

Chapter 13 also discusses the Saudi Aramco requirements to safeguard against possibledegradation or possible failures, as a result of the presence of static electricity, ofmicroelectronic components currently in use in communications and in process controlcomputers. The following specific topics are discussed in Chapter 13:

_ Definitions and Fundamentals_ General Requirements_ Protection of Specific Installations and Operations

Saudi Aramco Engineering Standards

Saudi Aramco Engineering Standard SAES-P-111 applies to the design and application ofequipment grounding for Saudi Aramco electrical installations. SAES-P-111 contains theminimum mandatory requirements for the design and the installation of equipment grounding.Any deviations from these requirements must have written approval from the Saudi AramcoChief Engineer in Dhahran. User/specifier requirements that exceed the minimumrequirements need no waiver approval even though they are different. SAES-P-111 containsthe minimum mandatory requirements for the design and the installation of the followingtypes of grounds:

_ Equipment Grounding_ Fence Grounding_ Tank Grounding_ Lightning Protection




IEEE Standards

IEEE Standards give information on how to design, specify, test, and measure equipment.This information is the consensus opinion of a group of subject matter experts. The IEEEstandard that applies to the design and the application of equipment grounding is IEEEStandard 142. The following sections of IEEE Standard 142 contain information onequipment grounding:

_ Section 2_ Section 3

Section 2

Section 2 of IEEE Standard 142 is titled "Equipment Grounding." Section 2 discusses theproblems caused by connection of the frames and the enclosures of electrical apparatus (suchas motors, switchgear, transformers, buses, cables, conduits, building frames, and portableequipment) to a ground system. Section 2 outlines the fundamentals of making theinterconnection system or the ground-conductor system between electrical equipment and theground rods. The following specific topics are discussed in Section 2:

_ Basic Objectives_ Fundamental Concepts_ Equipment Grounding as Influenced by Type of Use_ Outdoor Open-Frame Substations_ Outdoor Unit Substations_ Outdoor Installations Serving Heavy Portable Electric Machinery_ Interior Wiring Systems_ Interior Unit Substations and Switching Centers

Section 3

Section 3 of IEEE Standard 142 is titled "Static and Lightning Protection Grounding."Section 3 discusses the problems (such as how static electricity is generated) associated withstatic electricity, what processes produce static electricity, what must be done to prevent staticelectricity generation, or what must be done to drain static electric charges to earth to preventsparking. Section 3 also discusses the methods for protection of structures against the effectsof lightning. The following specific topics are discussed in Section 3:

_ Static Grounding_ Lightning Protection Grounding




National Electrical Code (NEC)

The purpose of the NEC is to practically safeguard persons and property from the hazards thatcan arise due to the use of electricity. NEC Article 250, titled "Grounding" applies toequipment grounding at Saudi Aramco electrical installations. Article 250 discusses thegeneral requirements for the grounding or the bonding of electrical installations. Groundingand ground system installation must be in accordance with Article 250 (as supplemented bySAES-P-111). The following specific sections of Article 250 apply to equipment grounding:

_ Section A, General Requirements_ Section B, Enclosure Grounding_ Section E, Equipment Grounding_ Section F, Methods of Grounding_ Section G, Bonding_ Section H, Grounding Electrode System_ Section J, Grounding Conductors_ Section K, Grounding Conductor Connections_ Section L, Instrument Transformers, Relays, Etc.




BASIS FOR INSTALLING EQUIPMENT GROUNDS IN SAUDI ARAMCOELECTRICAL SYSTEMS

The installation of equipment grounds at Saudi Aramco is based on solid ElectricalEngineering practices. These practices are determined by known parameters or well-documented theories.

This section provides information on the following topics:

_ Voltage Exposure_ Minimum Equipment Damage_ Isolation of Fault_ Minimize Electric Noise in the System

Voltage Exposure

Voltage exposure is defined as the unintentional contact between an energized electricalconductor and the metal frame or the structure that encloses (or is adjacent to) the conductor.This unintentional contact causes the metal frame or the structure to become energized at thesame voltage level that exists in the energized conductor.

The method for reducing the possibility of voltage exposure is to install an effectiveequipment grounding conductor on the metal frame or the structure that encloses theenergized conductor. An effective equipment grounding conductor must provide a lowimpedance path from the metal frame (or structure) to the zero-potential ground referencejunction that is located at the equipment power supply. The impedance of the groundingconductor must be low enough to carry full ground-fault current without creating animpedance (IZ) voltage drop large enough to be dangerous to personnel.

Minimum Equipment Damage

Electrical equipment that does not have an equipment ground connection or that has animproperly installed equipment ground connection can easily be damaged under ground faultconditions. The damage can be caused by the heat that is produced from the increased currentflow, the magnetic forces that are produced from the increased current flow, or the energy thatis released from an arcing ground fault. The possibility of the occurrence of equipmentdamage depends on the following variables:

_ The length of time that the ground fault current is allowed to flow(amount of time before protective devices isolate the ground fault).




Minimum Equipment Damage (Cont'd)

_ The magnitude of the ground fault current.

_ The resistance of the equipment ground return path.

_ The type of conductors that are used as the ground return path (insulatedor non-insulated).

The possibility of equipment damage increases with the length of time that the ground faultcurrent is allowed to flow. This length of time can be minimized by ensuring that a sufficientamount of ground fault current is available to quickly operate the protective equipment. Themajor step involved in providing a sufficient amount of ground fault current is to ensure thatthe equipment ground return path has the lowest possible impedance. A low impedanceground return path can be achieved through use of the following techniques:

_ The installation of only safety-listed ground return path components.

_ The interconnection of all equipment grounding conductors to acommon grounding electrode system.

_ The elimination of the use of separate isolated or dedicated groundingconductors.

_ The elimination of the use of actual earth as part of the equipmentground return path.

_ The use of proper bonding methods when the conductors in theequipment ground return path are connected.

_ The installation of equipment grounding conductors so that theconductors are physically running with the equipment powerconductors.

_ The installation of equipment grounding conductors so that the faultloop area is small.

_ Proper protection corrosion of all terminated/spliced connections of thegrounding conductors.




Minimum Equipment Damage (Cont'd)

The possibility of equipment damage also increases with the magnitude of the ground faultcurrent. The maximum amount of ground fault current that can flow in a circuit is equal tothe phase voltage of the circuit divided by the total impedance of the ground return path. Themaximum amount of ground fault current can only be reduced through insertion of impedancein the ground return path. The maximum amount of ground fault current should not belimited to less than 10 to 15 times the current rating of the ground fault protective devices toensure that sufficient ground fault current is available to operate the ground fault protectivedevices. The only step that can be taken to reduce the possibility of equipment damage fromexcessive ground fault currents is to ensure that all of the components in the ground returnpath are rated to carry the maximum ground fault current.

The possibility of equipment damage also increases with the amount of impedance in theequipment ground return path. The portions of the equipment ground return path that aremost likely to result in an increase in the impedance of the ground return path are the bondingconnections between the conductors. The following steps can be taken to reduce thepossibility of high resistance bonding connections between conductors:

_ The bonding surfaces should not be painted.

_ Simple screw connections should not be relied on to make an adequatebonding connection between two pieces of sheet metal.

_ The bonding surfaces should not be made from raw (untreated) metal.

_ The bonding surfaces should not be made from dissimilar metals.

_ The bonding connection should be made through use of approvedcompression hardware, brazing, or welding. Bonding connectionsshould not be made through use of soldering.

The possibility of equipment damage also increases with the use of non-insulated equipmentground conductors. Large voltage differences can exist between components such asraceways and a non-insulated equipment ground conductor under ground fault conditions.This voltage difference can cause arcing between the non-insulated equipment groundconductor and the raceway. This arcing can damage adjacent conductors. The possibility ofequipment damage from non-insulated equipment ground conductors can be eliminatedthrough use of insulated equipment ground conductors.




Isolation of Faults

An electrical fault is defined as a physical condition that causes a device, a component, or anelement to not perform in a required manner. Although this definition applies to all types ofelectrical faults, this section is only concerned with ground faults. The specific definition of aground fault is an insulation failure between a conductor and a ground or a frame.

The following methods of system grounding are used in Saudi Aramco electrical systems:

_ Solid grounding_ Resistance grounding_ Impedance grounding_ Ungrounded

The method of system grounding that is applied in a given Saudi Aramco electrical systemhas no bearing on the method of equipment grounding for use in a Saudi Aramco electricalsystem. The only method of equipment grounding is to connect a suitable conductor sizebetween the noncurrent-carrying metal parts of all equipment, raceways, and other suchenclosures and the system ground conductor and/or the grounding electrode conductor. Theuse of this method of equipment grounding will allow the protective devices to quickly isolatethe ground faults should a ground fault occur.

The following two types of protective devices are used to isolate ground faults:

_ Fuses_ Circuit Breakers_ E2 starters for H.V. motors or NEMA starts for low voltage motors

Figure 1 shows the use of fuses to isolate a ground fault in a motor. The fuses that are shownin Figure 1 contain internal conductors or links that melt when the current that is passingthrough the fuse exceeds the rating of the fuse. The fuse isolates a ground fault throughreaction of an open circuit when the internal link melts. The following sequence of eventsoccurs during the isolation of a ground fault in a motor by fuses:

_ A ground fault develops between one of the motor windings and themotor enclosure.

_ Ground fault current in excess of the rating of the fuses begins to flowfrom the transformer secondary windings through the fuses.




Isolation of Faults (Cont'd)

_ The ground fault current flows through the motor windings to the motorenclosure through the ground fault.

_ The ground fault current causes the internal links in the fuses to melt.This melting creates an open circuit and isolates the ground fault.

Use of Fuses to Isolate a Ground Fault in a MotorFigure 1





Figure 2 shows the use of circuit breakers to isolate a ground fault in a motor. The circuitbreaker (52) shown in Figure 2 functions as a switch to open and to close the circuit thatconnects the transformer secondaries to the motor. However, the circuit breaker cannot sensethe ground faults. The circuit breaker must use ground sensing relays to detect a ground fault.The ground sensing relays (50GS) send an input signal to the circuit breaker control circuitwhen a ground fault occurs. The input signal then causes the circuit breaker to open. Thisopening of the circuit breaker isolates the ground fault. The following sequence of eventsoccurs during the isolation of a ground fault in a motor by circuit breakers:

_ A ground fault develops between one of the motor windings and themotor enclosure.

_ The ground fault current flows through the motor windings to the motorenclosure through the ground fault.

_ The ground fault current then flows through the motor enclosure to theseparate equipment ground conductor and back to the power sourcethrough the system ground.

_ The ground fault current in excess of the setpoints of the 50GS groundsensing relays begins to flow from the transformer secondary windingsthrough the current transformers to the 50GS ground sensing relays.

_ The ground fault current that flows through the current transformers ofthe 50GS ground current sensing relays causes the 50GS ground sensingrelays to activate.

_ The 50GS ground sensing relays send a signal to the circuit breaker (52)that causes the circuit breaker to open to interrupt the power and toisolate the ground fault.





Use of Circuit Breakers to Isolate a Ground Fault in a MotorFigure 2

Minimize Electrical Noise in the System

Noise is defined as an electrical disturbance on a circuit that interferes with or that preventsthe reception of signals or of information. The circuits most effected by noise are digitalcircuits, computer circuits, instrumentation circuits, and communication circuits.

The following types of disturbances are classified as noise; each type of disturbance has aslightly different effect on the circuit.

_ Impulse noise jitter




_ Crosstalk_ Hum




Minimize Electrical Noise in the System (Cont'd)

Impulse noise jitter is a transient disturbance separated in time by quiescent intervals.Impulse noise jitter can cause interruptions in communication circuits, digital circuits, andcomputer circuits. Instrumentation circuits (particularly 4-20 mA circuits) are not seriouslyeffected by impulse noise jitter.

Crosstalk is an extraneous signal introduced to a circuit from an adjacent circuit carrying ACor pulse-type signal. The effect of crosstalk on a given circuit depends on the magnitude ofthe extraneous signal introduced and the magnitude of the adjacent AC or pulse-type signalthat is creating the crosstalk. Crosstalk can cause unwanted acoustic sound in communicationcircuits and inadvertent operations in other types of circuits. Crosstalk also represents apower loss to the circuit that is causing the crosstalk.

Hum is similar to crosstalk because hum is also an extraneous signal that is introduced to acircuit from an adjacent circuit. The term "hum" is normally used in reference to a constant60 Hz or 400 Hz extraneous audio signal. The term "crosstalk" is normally used in referenceto a transient or intermittent extraneous audio signal. Hum affects a circuit by masking of thedesired signal.

The problem that is caused by noise in a circuit is the creation of a signal error. Signal error isthe sum or the difference between the normal circuit signal and the noise signal. Signal errorscan cause electronic circuit functions ot operate before or after the design setpoint of thefunction.




DETERMINING THE EQUIPMENT GROUNDING REQUIREMENTS FOR SAUDIARAMCO ELECTRICAL SYSTEMS

Each piece of equipment must be grounded in order to provide the maximum protectionagainst the inadvertent energization of the metal frame structure of a piece of equipment.

This section provides information on the following topics:

_ Single Point Grounding_ Grounding Conductor_ Conduit Grounding_ Connections to Earth_ Bonding_ Motor/Generator Grounding_ High Voltage Switch Grounding

Single Point Grounding

Single point grounding is defined as a method of equipment grounding in which there is onlyone connection to earth ground. Single point grounding is used in electronic instrumentationand communication circuits to help eliminate the noise that can be created due to the flow ofground loop currents. Ground loop currents are eliminated because a complete path forcurrent flow from a ground connection at one potential to a ground connection at a differentpotential does not exist when there is only one connection to earth ground.

Single point grounding is only effective in circuits that operate below 50 kHz. Circuits thatoperate above 50 kHz will have multiple connections to earth ground due to the capacitivecoupling to ground that occurs at high frequencies.

Grounding Conductor

All Saudi Aramco electrical equipment must be grounded through use of a groundingconductor. A grounding conductor is defined as a conductor that is used to connectequipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Each piece of electrical equipment should be connected to the system grounding electrodethrough use of a separate equipment grounding conductor. Equipment grounding conductorsshould not be looped from one piece of electrical equipment to a different piece of electricalequipment. Equipment grounding conductors should also be continuous (not cut or spliced).




Grounding Conductor (Cont'd)

Equipment grounding conductors must be made from soft-drawn copper wire or, in case ofground rods, copperweld wire. The conductors should be installed so that the conductor isprotected from mechanical damage.

SAES-P-111 covers the selection and installation of grounding conductors. The followingsizes of wires are preferred by Saudi Aramco for grounding conductors for standardization:

_ No. 4 AWG Stranded or Solid_ No. 2 AWG Stranded or Solid_ No. 1/0 AWG Stranded_ No. 2/O AWG Stranded_ 250 MCM Stranded_ No. 4/O AWG Stranded_ 350 MCM Stranded_ 500 MCM Stranded_ 750 MCM Stranded

The grounding connection will be made through use of thermite welding, brazing, orapproved compression grounding connections (Burndy Hyground System or equivalent).Bolted or a ready means of disconnection for testing purposes, such as bolted connections,shall be provided in the grounding connection to the following:

_ Generator neutrals_ Transformer neutrals_ Grounding electrodes such as grounded well or groups of grounded

rods.

The sizing of the ground conductor is dependant on the voltage level and the short circuit ofthe power system of the electrical system to which the equipment is connected. Theconductor size for the higher voltage system should be used for mixed voltage systems. Thevoltages are broken down as follows:

_ Conductor sizes - systems 600V and below_ Conductor sizes - system over 600V





Conductor Sizes - Systems 600V and below

The size of the copper grounding conductors for power source transformer tanks, transformerneutrals, main switchboards, or other equipment that is supplied directly from the LV (lowvoltage) side of a transformer, without an intervening protection device in a system rated600V and below, depends on the following:

_ The kVA rating of the power source transformer.

_ The type of protection that is provided for the primary winding of thelower source transformer (e.g., fuses or circuit breakers).

Section 1 of Work Aid 2 contains the formula, the table, and the procedure for use indetermining the size of the grounding conductors that were previously described.

The size of equipment grounding conductors for equipment that is beyond the mainswitchboard or the transformer output protection device in systems rated 600V and belowmust comply with Article 250-95 of the National Electrical Code (NEC). Article 250-95states that the size of the equipment grounding conductor is based on the rating of theautomatic overcurrent device in the circuit that is ahead of the equipment. Section 2 of WorkAid 2 contains a procedure and a table for use in determining the size of the equipmentconductors that were previously described.

Conductor Sizes - Systems Over 600V

The size of the grounding conductor for electrical systems over 600V is based on thefollowing type of system grounding that is used.

_ Solidly Grounded Systems_ Impedance Grounded Systems

Solidly Grounded Systems - Grounding conductor sizes for solidly grounded systemsover 600V are based on the three-second, short-time current capabilities of the circuitbreaker that is ahead of the grounding conductors. The three second, short-timecurrent capability must be derived through use of a formula in cases where a circuitbreaker is not installed or where a three-second, short-time current capability is notassigned.





Section 3 of Work Aid 2 contains the formula, the table, and the procedure for use indetermining grounding conductor sizes in solidly grounded systems over 600V. Thissection of Work Aid 2 applies to determination of the size of all grounding conductorsin grounded systems over 600V. These grounding conductors include the following:

_ Equipment grounding conductors (Column 2 of the table)_ Neutral grounding conductors (Column 2 of the table)_ Ground bus conductors (Column 2 of the table)_ Ground grid conductors (Column 3 of the table)

Impedance Grounded Systems - Grounding conductor sizes for impedance groundedsystems over 600V are based on the ten second rating of the neutral grounding device,or the ten second rating of the combined neutral grounding devices for systems thathave multiple grounding devices that are connected in parallel. This basis applies tomost impedance grounded installations. The two exceptions to the basis for the sizingof grounding conductors in impedance grounded systems over 600V are as follows:

_ A minimum grounding conductor size of No. 2/0 AWG must be usedfor all installations to ensure that the conductor has sufficientmechanical strength.

_ The three-second, short-time current capability of an equivalent solidlygrounded system is the basis for the size of the grounding conductorswhen there is a possibility of two- or three-phase fault current flowingthrough the grounding conductor.

Section 4 of Work Aid 2 contains the table and the procedure to be used to determinegrounding conductor sizes in impedance grounded systems over 600V. This section ofWork Aid 2 applies to determining the size of all grounding conductors in impedancegrounded systems over 600V. These grounding conductors include the following:

_ Equipment grounding conductors (Column 2 of the table)_ Neutral grounding conductors (Column 2 of the table)_ Ground bus conductors (Column 3 of the table)_ Ground grid conductors (Column 4 of the table)




Conduit Grounding

Conduit must be satisfactorily grounded to prevent creating electrical shock hazards due tovoltage exposure. A faulted conductor that contacts metal conduit will raise the conduit to thevoltage level of the failed conductor. A person that contacts this energized conduit andground will receive an electrical shock unless the conduit is satisfactorily grounded. Allconduits must be directly grounded regardless of the system voltage.

Conduit that does not comply with the termination methods listed above must have a separategrounding connection bonded to both ends of the conduit. Metal conduit that containsconductors of systems above 600V must also have a separate grounding connection bonded toboth ends of the conduit.

Connections to Earth

A very important aspect of grounding equipment is the final connection to the earth. Thissection provides information on the methods for use in making ground connections to earth inthe following locations:

_ Below Ground Line_ Above Ground Line

Below Ground Line

Saudi Aramco uses the following approved methods for ground connections below groundline:

_ Thermite Welded Connections_ Brazed Connections_ Compression Connections

Thermite Welded Connections - Thermite welding is an exothermic process for use inmaking electrical connections between two pieces of copper or between copper andsteel. The thermite welding process does not require an outside source of heat toproduce the weld. The weld is produced by mixing powdered aluminum and iron orcopper oxide in a container and by placing this mixture in a graphite crucible (mold).The mixture is then ignited through use of a flint lighter, which starts the highlyexothermic reaction. The heat from the exothermic reaction turns the two metals into asuperheated liquid that flows through and around the conductors to be joined, thuswelding the conductors together.




Connections to Earth (Cont'd)

An electrical connection produced from the thermite welding process has thefollowing characteristics:

_ The current-carrying capacity of the connection will be equal to thecurrent- carrying capacity of the conductors.

_ The connection will be permanent and will not loosen or corrode.

Ground connections between the equipment ground conductors and the earthelectrodes that are made through use of thermite welding must also be equipped with aseparate disconnecting means, such as bolted joints. The separate disconnectingmeans must facilitate separation of the equipment ground from the system groundduring testing.

Brazed Connections - Brazed connections are for use in making electrical connectionsbetween the following:

_ Two grounding conductors_ A ground conductor and an earth electrode_ A ground conductor and a lug

A brazed connection is made by placing together the two surfaces to be joined andthen applying heat to the surface through use of a torch. The two surfaces arepreheated with the torch, and then a copper alloy filler material is applied to thesurfaces to be joined. The filler material will melt when heated by the torch and willflow through and around the surfaces to be joined. The filler material solidifies andfuses the two surfaces together after the heat is removed. The electrical connectionthat results from brazing has characteristics that are similar to the characteristics of athermite welding connection. Thermite welding connections are preferred over brazedconnections because thermite welding connections require fewer skills, lessequipment, and less time to install than brazed connections.

Compression Connections - A compression connection is made by placing a compressionfitting (lug) over the end of the grounding conductor and by crimping the fitting to theconductor through use of a special compression tool and die. The only approvedcompression connectors for use in making ground connections in Saudi Aramcoelectrical systems are Burndy Hyground Systems or an equivalent. An acceptablecompression grounding connection must have the following characteristics:




Connections to Earth (Cont'd)

_ Freeze-thaw cycling tests should not significantly change the resistanceof the connector-conductor assemblies and should not impair the abilityof the assemblies to function properly when exposed to a short circuittest to failure.

_ The tensile strength and the torque strength of the connection jointshould be greater than the tensile strength and the torque strength of theconductor.

_ The grounding connector must be able to stand, without damage, arepeated, short-circuit current load that is equal to 80 percent of theshort circuit of the conductor.

_ Heat cycles with sufficient current to raise the conductor temperature to350oC followed by short circuit tests should not damage the groundingconnector.

_ The sequential aging test (sequential heat cycle, freeze-thaw cycle, saltspray test, heat cycle, and short circuit) should not damage thegrounding connector.

_ Heat cycles that have sufficient current to raise the conductortemperature to 350oC that are followed by a corrosion test in which thetest sample is immersed in a 20 percent nitric acid solution and thenfollowed by a short-circuit test should not damage the groundingconductor.

_ The connector should be marked with the cable size that isaccommodated and with the DIE index number.

_ The compression tool that is used on the connector should be designedto lock in during compression and to be released only after thecompression stroke is completed or when a safety release trigger isactivated.

_ After compression, the DIE should leave a mark on the connector thatmatches the original DIE index number on the connector.

Above Ground Line




For ground connections that are made above the ground line in Saudi Aramco electricalsystems, the three methods that apply to ground connections made below the ground line mustbe used, in addition to bolted connections.




Bonding

Bonding is defined as the permanent joining of metallic parts to form an electricallyconductive path that will assure electrical continuity and the capacity to safely conduct anycurrent likely to be imposed.

There is a difference between equipment bonding and equipment grounding. Equipmentbonds are installed to ensure that continuity exists between all the noncurrent-carrying metalportions of electrical equipment. Equipment grounds are installed to ensure that continuityexists between the noncurrent-carrying metal portions of electrical equipment and an earthground. Equipment bonds should be installed when it is possible that continuity will not existbetween one noncurrent-carrying metal portion of electrical equipment and the noncurrent-carrying metal portion of the electrical equipment that is connected to the equipment groundconductor. Figure 3 shows an example of when an equipment bond should be installed.

Equipment BondFigure 3




Figure 3 shows that the equipment ground conductor is terminated at the ground terminal onthe back of the noncurrent-carrying, metal outlet box. Figure 3 also shows an equipmentbonding jumper that connects the noncurrent-carrying metal portions of the receptacle to theground terminal. This bonding connection is necessary to ensure that there is continuitybetween the noncurrent-carrying metal portions of the receptacle and the noncurrent-carryingmetal outlet box.




Bonding (Cont'd)

Equipment bonding is accomplished through use of approved bonding jumpers. Thefollowing are examples of approved bonding jumpers:

_ Bonding screws that are included as part of electrical equipment for thesole purpose of equipment bonding.

_ A copper conductor with approved lugs that are attached to both ends ofthe conductor.

_ Approved threaded couplings and approved threaded bosses onenclosures.

_ Approved threaded couplings and connectors on conduit.

_ Approved bonding-type locknuts and bushings.

Motor/Generator Grounding

Saudi Aramco requires the frames of generators to have at least two grounding connectionsand the generator prime mover to have a separate grounding connection. Saudi Aramco alsorequires motor frames to have at least one grounding connection.

Care should be taken to ensure that insulated components, such as insulated bearing pedestals,remain ungrounded. A shorting strap should be installed across the insulation on the couplingend to maintain the motor frame at ground potential. This shorting strap should contain a testlink that is to be removed when the bearing insulation is tested. The bearing on the non-coupling end of the motor should remain insulated at all times to prevent shaft currents.

High Voltage Switch Grounding

For high voltage disconnecting switches to be hand operated, an operator must be presentnear a grounded structure, at a point where an opening of an energized circuit or a mechanicalfailure and electrical breakdown of the switch insulator could result in an arc to the structure.Because a large percentage of fatal accidents is associated with the operating handles of highvoltage switches, high voltage switches must be grounded.




High Voltage Switch Grounding (Cont'd)

A metallic platform should be provided for the operator of a disconnecting switch that is rated34.5 kV and above. This platform should be bonded with a 120 sq. mm (No. 4/0 AWG)stranded copper conductor to the operating handle or crank of the disconnect. The operatingmechanism should be directly connected to the grounding system by means of a 120 sq. mm(No. 4/0 AWG) stranded copper conductor. The platform should have no direct connection tothe ground system. For fault current from the operating handle to ground, these connectionswill ensure a direct path that will avoid the operator's platform. The operator's hands and feetwill remain at the same potential.

Disconnects (but not their mechanisms) and insulator anchorages on steel structures may relyon the steel structure itself for equipment grounding. Each leg of the steel structure should begrounded, at a point near the base of the structure, with a conductor that is appropriate to theequipment mounted on the structure. All other equipment on steel structures should have aseparate grounding conductor. The conductors should be supported along the structure at 0.9m (3 ft.) intervals through use of clamps.




DETERMINING THE STATIONARY EQUIPMENT GROUNDING REQUIREMENTFOR SAUDI ARAMCO ELECTRICAL INSTALLATIONS

For the purpose of this section, the term "stationary equipment" will be defined by the list ofitems given below. Other sections of this module will cover mobile equipment grounding,building and structure grounding, offshore platform grounding, and digital equipment(computer) grounding.

_ Generators and Motors_ Switchboards, Switchgear, Motor Control Circuits_ Transmission Substations_ Transmission Lines_ Overhead Distribution_ Industrial Plant Areas_ Distribution and Utilization Equipment_ Cable Sheaths_ Fences_ Instruments, Meters, Relays, and Instrument Transformers_ UPS System and Batteries

SAES-P-111 and SADP-P-111 present the following general guidelines concerninggrounding requirements for stationary equipment in Saudi Aramco installations:

_ All accessible non-current carrying metal parts of electrical equipmentshould be grounded. All accessible metal parts of non-electricalequipment should be grounded if they are likely to become energizedunder abnormal conditions.

_ Equipment should be grounded by means of grounding conductor(s)connecting the equipment to a ground bus, ground grid, or othergrounding electrode.

_ The grounding conductor termination at the equipment must be at thestuds or holes provided by the equipment manufacturer. Thetermination point on equipment above 600V should be specified toNEMA standard 15 mm (9/16 in) holes, 1/2 in studs, or 45 mm (1-3/4in) centers. When the manufacturer does not provide a groundingconductor termination point, the grounding conductor must beterminated on a main structural part of the equipment with an approvedlug or clamp. Lugs must be brazed or hydraulically crimped. Paint is tobe removed to give a bare metal mating surface. On completion, thewhole termination is to be bitumen painted (bitumastic No. 50 or equal)for protection against corrosion.




_ Equipment and system grounds are to be connected to the ground bus orto the ground grid by separate conductors.

_ A grounding bus is to form a closed loop so that the equipment groundsand the system neutrals that are connected to the grounding bus havetwo current paths to the main ground electrode.

_ Conduit, cable tray, cable armor, or cable shield is not to be the solemeans of grounding equipment. A segment equipment groundingconductor also must be installed in the conduit, cable tray, cable, orcord. Metallic conduit and cable tray is to be grounded at both endpoints.

_ Generators and motors larger than 185 kW (250 HP), powertransformers, switchgear ground buses, and similar equipment are tohave a minimum of two grounding connections to a made electrode or aground grid.

_ The shields and the armor of power cables are to be grounded at bothends. The continuity across splices is to be maintained through bondingacross the splices.

Generators and Motors

As previously explained, the grounding requirements of SAES-P-111 and SADP-P-111 forgenerators and motors are as follows:

_ The frames of generators are to have at least two grounding connectionsand the prime mover is to have its own grounding connection. Motorframes are to have at least one grounding connection.

_ The insulated components that are associated with the prevention ofshaft circulating currents are to be left ungrounded (e.g., such asinsulated pedestals or insulated bearings). A shorting strap is to beinstalled across the insulation on the coupling end of motors to maintainthe motor frame at ground potential when horizontal motors aresupplied with both pedestals insulated. This shorting strap is to containa test link that is to be removed when the bearing insulation is tested.The bearing on the non-coupling end of the motor shall remain insulatedat all times to prevent shaft currents.




Switchboards

SAES-P-111 and SADP-P-111 establish the following grounding requirements forswitchboards:

_ All switchboards are to be equipped with a grounding bus that runs thelength of the switchboard and that is mounted in or on the switchboard.This grounding bus is usually supplied by the manufacturer. Thegrounding bus is to be connected at each end to the installation groundbus or ground grid.

Transmission Substations

SAES-P-111 and SADP-P-111 contain the grounding requirements for transmissionsubstations. These requirements are sub-divided as follows:

_ Power Transformers and Potential Transformers_ Circuit Breakers_ Disconnects_ Lightning Arresters_ Substation Equipment on a Steel Structure_ Substation Equipment on a Wood Structure

Power Transformers and Potential Transformers

The equipment grounding connections are to be separate from the system or neutralgrounding connection. Power transformer tanks due to have two grounding connections.Cooler banks, control kiosks, and other such equipment associated with power transformersare to have separate grounding connections.

Circuit Breakers

Circuit breakers with separate pole construction are to have a separate grounding connectionto each pole. Operating mechanisms are to have a separate connection unless the mechanismis integral to the breaker.




Transmission Substations (Cont'd)

Disconnects

A metallic platform is to be provided for the operator of a disconnecting switch. Thisplatform is to be bonded with 120 mm2 (No. 4/0 AWG) stranded copper to the operatinghandle or the crank of this disconnect. The operating mechanism shall be directly connectedto the grounding system by means of 120 mm2 (No. 4/0 AWG) stranded copper, and theplatform shall have no direct connection to the ground system. These connections ensure thata direct path for fault current from the operating handle to the ground will enable current toavoid the operator's platform.

Lightning Arresters

The grounding terminals of lightning arrestors shall be directly connected to the ground gridor ground bus with a minimum of bends. The grounding conductor shall be of a sizeappropriate to the other equipment on the same system, and the conductor shall not be runthrough any conduit or metal enclosure. The grounding conductor is to have no 90 degreebends and is to be as short as possible to the ground grid.

Substation Equipment on a Steel Structure

Provided that the structure is grounded, disconnects (but not the operating mechanisms) andinsulator anchorages on steel structures can use the steel structure itself for grounding. Eachleg of the steel structure shall be grounded at a point near the structure base with a conductorappropriate to the equipment mounted on the structure. All other equipment on the steelstructures shall have separate grounding conductors. The conductors shall be supported at 0.9m (3 ft) intervals through the use of clamps.

Substation Equipment on a Wood Structure

All electrical equipment (e.g., transformers, disconnects, insulated anchorages) and the steelassociated with the electrical equipment (e.g., steel platforms and cross-arms) are to begrounded to the same standard as other equivalent electrical equipment in the substation.




Transmission Lines

SAES-P-111 and SADP-P-111 establish the following grounding requirements fortransmission lines:

_ The continuation of the transmission line's overhead ground wiresacross the substation protects transmission line substations against directlightning strikes. These overhead ground wires can be supplementedwith earth masts, peaks, heights or shielding angles.

_ The overhead ground wires that are terminated on a substation steelstructure must be jointed through use of a bi-metal connector to anequivalent cross section copper conductor that is connected to thegrounding grid or bus.

_ The grounding downlead of wood pole structures that are insidesubstations, that are in the immediate vicinity of substations, or that arewithin plant areas having a ground grid must be connected (by buriedconductor) to the ground grid. The pole butt wrapping must be retainedon these structures.

Overhead Distribution

SAES-P-111 and SADP-P-111 establish the following grounding requirements for overheaddistribution:

_ At transformer locations, where a system ground (600V or below) isestablished, the connections linking transformer neutral, system neutralconductor, transformer tank(s) and any system disconnecting devicesmust be sized in accordance with Sections 1 and 2 of Work Aid 2. Thedownlead must also be of the same size if connected to an extensiveground grid or bus. If the downlead connects solely to a local, madeground, an 8 mm (5/16 in) copperweld, 8 foot ground rod(s) must beused.

_ At other locations, and at all other voltages, the equipment and the metalhardware must be grounded through use of a minimum 25 mm2 (No. 4AWG) conductor or of an 8 mm (5/16 in) copperweld ground rod.Downleads and pole butt wrappings must be 8 mm (5/16 in)copperweld. Pole downleads within industrial plant areas having aground grid must be connected to the ground grid with a conductorwhose minimum size is 25 mm2 (No. 4 AWG).




Overhead Distribution (Cont'd)

_ PVC insulated grounding conductor must be used for downleads.

_ Disconnects that are rated above 600 V, that are operated from amechanism at ground level, and that are located in plant areas where aground grid exists are to be treated as disconnects in a transmissionsubstation.

Industrial Plant Areas

SAES-P-111 and SADP-P-111 establish the following grounding requirements for industrialplant areas:

_ Grounding conductors must be installed such that a metallic groundingconnection must exist from all equipment to the neutrals of all systemslocal to the plant area.

_ Equipment above 600V must be connected to the ground grid when aground grid is provided. When a ground grid is not provided, theequipment above 600V must be connected to the system neutral bymethods that conform to NEC Articles 250-57 and 250-91 (b).

_ For grounding equipment 600V and below, the Distribution andUtilization Equipment guidelines are to be used.

_ Where a transmission voltage substation is located within or adjoiningan industrial plant area, a ground grid must be established in the plantarea. This grid must consist of sufficient conductors to pick up theequipment grounds. The ground grid must be designed in conjunctionwith the transmission voltage substation ground grid. All pipelinesentering and exiting vital facilities are to be buried 18 m on either sideof the security fence.

The equipment grounding conductor that is run with or that encloses the circuit conductorsmust be a copper conductor or other corrosion-resistant conductor. This conductor can besolid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar.




Distribution and Utilization Equipment

SAES-P-111 and SADP-P-111 establish the following grounding requirements fordistribution and utilization equipment:

_ A multiple grounded neutral system (whether cabled or overhead) is tobe used in residential and non-industrial locations. The neutralconductor is taken to all locations on the system and is grounded atpoints of utilization. In overhead systems, the neutral conductor is alsogrounded at each pole. Grounding at points of utilization must be inaccordance with the National Electrical Code, Article 250-H, GroundingElectrodes, except that the water piping must not constitute thegrounding electrode, but it is to be bonded to the grounding electrode.Equipment at points of utilization is to be grounded by connection to themultiple grounded neutral and the local electrode.

_ A single-point grounded neutral system is to be used in industrial plantswhere cabling will normally predominate. The neutral is to be groundedat the transformer only and cannot be brought out for system use.

_ Utilization equipment is to be grounded by a metallic connection to thesystem neutral and to the ground grid or ground bus. The groundingconnection is to conform to Articles 250-57 and 250-91 (b) of theNational Electrical Code.

The ground loop impedance of the circuit that is formed by the line conductor from the powersource to the equipment and by the grounding path from the equipment back to the powersource neutral must be low enough to allow sufficient fault current to pass to operate theprotection device. The following equation should be satisfied:




Distribution and Utilization Equipment (Cont'd)

where: Zgl = ground loop impedance, ohms

E = line to neutral voltage, V

I = current rating of fuse or trip setting of overcurrent device,A

K = constant, 3 for fuses, 1.5 for other overcurrent devices

Difficulties in attaining an adequately low value of Zgl are unlikely to arise but can occur atlow voltages/high ratings.

Residential occupancies must have ground-fault circuit protection for all 115V, 15A, and 20Areceptacle outlets or feeders supplying the outlets that are installed outside or in bathrooms.

Construction sites are to have ground-fault circuit protection for all 115V, 15A, and 20Areceptacle outlets or feeders supplying the outlets that are not part of the permanent wiring.

Conduit is not to be the sole means of grounding equipment, except for overhead lightingwithin buildings that are installed with rigid conduit.

A bonding jumper is to be installed at flush-mounted, grounding-type receptacles to connectthe receptacle grounding terminal and the box. Reliance is not to be placed upon contactdevices or yokes to provide the connection (exception 2 of NEC, Article 250-74 is excluded).

Lighting fixture outlet boxes are to be grounded and a bonding jumper is to be installed toconnect the fixture to the box.




Cable Sheaths

SAES-P-111 and SADP-P-111 establish the following grounding requirements for cablesheaths:

_ The lead sheaths, the shields, and the armor of multi-conductor powercable must be bonded and grounded at both ends. The continuity atsplices is to be assured by bonding across the splice. Steel wire armor isto be bonded and grounded at both ends but must not constitute agrounding conductor.

_ The metallic sheath and the armor, if any, of single core power cablesbelow 240 mm2 (500 MCM) is to be bonded and grounded at bothends. At 240 mm2 (500 MCM) and above, short lengths (such as roadcrossings and line terminations into substations) are to be treatedsimilarly.

_ Terminators for aluminum sheathed cable are to be the positivegrounding type, with positive ground set screws. OZ type terminators(SPKHK/SPKGK or similar) are to be specified for use with aluminumsheathed cable.

_ Signal cables used in instrumentation, telemetering, andcommunications are to have shields that are grounded only at one end toreduce the interference from stray sources.

Fences

SAES-P-111 and SADP-P-111 establish the following grounding requirements for fences:

_ For transmission substation fences, the peripheral conductor of theground grid is to be run 0.6 m to 1 m (2 to 3 ft) outside the fence andparallel to the fence. The fence is to be bonded to the peripheralconductor at maximum intervals of 6 m (20 ft) with a minimum of size70 mm2 (No. 2/0 AWG) conductors.

_ For industrial plant area fences where a ground grid is installed, aperipheral conductor is to be run 0.6 m to 1 m (2 to 3 ft) outside of andparallel to the fence. In cases where a common boundary existsbetween a transmission substation and an industrial plant, the fence is tobe run 0.6 m to 1 m (2 ft to 3 ft) inside the industrial plant fence. Thefence is to be bonded to the peripheral conductor at maximum intervalsof 15 m (50 ft) with a minimum of size 35 mm2 (No. 2 AWG)conductors.




Fences (Cont'd)

_ For distribution substation fences (13.8 kV and below), the peripheralconductor is to be run 0.6 m to 1 m (2 ft to 3 ft) outside of and parallelto the fence. The fence is to be bonded to the peripheral conductor atmaximum intervals of 15 m (50 ft) with a minimum of size 35 mm2(No. 2 AWG) conductors.

Instruments, Meters, Relays and Instrument Transformers

The grounding requirements for instruments, meters, relays, and instrument transformers arefound in SAES-P-111, SADP-P-111, NEC Articles 250-121, 122, 123, 124, 125 and SAES-J-31. These requirements are summarized as follows:

_ Secondary circuits of current transformers (CT) and potentialtransformers (PT) are to be grounded when the primary windings areconnected to circuits that have a potential of 300 volts or more toground. CT's or PT's mounted on switchboards are to be groundedirrespective of the voltage.

_ The cases or the frames of instrument transformers that are accessibleare to be grounded.

_ Instruments, meters, and relays operating with windings or workingparts that are energized by voltages less than 1000 volts are to begrounded as follows:

- Instruments, meters, and relays that are not located on switchboards,that operate with windings or working parts at 300 volts or more toground, and that are accessible are to have the cases and the otherexposed metal parts grounded.

- Instruments, meters, and relays (whether operated from current andpotential transformers or connected directly in the circuit) onswitchboards that do not have live parts on the front of the panels are tohave the cases grounded.

_ The grounding conductor for the secondary circuits of instrumenttransformers and for the instrument cases are not to be smaller than No.12 copper or No. 10 aluminum. The cases of instrument transformers,instruments, meters, and relays that are mounted directly on thegrounded metal surfaces of enclosures or grounded metal switchboardpanels are to be considered to be grounded. Additional groundingconductors are not required.




Example of Stationary Equipment Grounding

Assume that a new installation of an electrical motor is being planned and that the groundingrequirements have not yet been determined. The motor is a 250 HP, 480 volt, three-phasemotor. The full load current of the motor is 350A, and motor protection is provided through a500A inverse-time circuit breaker. This information can be used to determine that twogrounding conductors are required because the motor is at 250 HP. NEC Article 250-95A canbe used to determine that the grounding conductors must be at least a No. 2 AWG coppercable. One of the grounding conductors should be connected directly from the motor to theplant's grid. The other grounding conductor should be run with the motor's power conductorsfrom the motor to the motor's power source transformer, and then to the grid.




DETERMINING THE MOBILE EQUIPMENT GROUNDING REQUIREMENTS FORSAUDI ARAMCO ELECTRICAL INSTALLATIONS

Mobile equipment is defined as equipment mounted on wheels, treads, or other such devicesthat can easily be relocated.

The following Saudi Aramco Standards and NEC Sections provide guidance for groundingportable equipment:

_ Saudi Aramco Engineering Standards SAES-P-111

_ Saudi Aramco Design Practice SADP-P-111

_ NEC Section 250-6 covers portable generators and vehicle-mountedgenerators.

_ NEC Section 250-154 covers the special requirements for grounding ofhigh voltage (1 kV and above) portable or mobile equipment. Thissection applies to outdoor equipment such as power shovels, drag lines,or dredges.

_ NEC Section 400-C applies to multiconductor portable cables that areused to connect mobile equipment and machinery.

_ NEC Article 515 provides information on electrical and groundingsafety in bulk storage plants. Bulk storage plants are locations whereflammable liquids are received by tank vessel, tank car, or tank vehicle.

_ NEC Section 550-4(a) covers mobile homes that are not intended asdwelling units. A particular application of this Article would beelectrical installations at construction sites where trailers are required.




DETERMINING MOBILE EQUIPMENT GROUNDING REQUIREMENTS FORSAUDI ARAMCO ELECTRICAL INSTALLATIONS (CONT'D)

SADP-P-111 contains the following sections on the grounding of mobile equipment:

_ Cranes and Mechanical Handling Equipment_ Portable Equipment

Cranes and Mechanical Handling Equipment

The grounding requirements for Cranes and Mechanical Handling Equipment are found inSAES-P-111 and SADP-P-111 as follows:

_ The grounding practices should avoid the passage of ground currents(either ground fault or arc welding return currents) through the bearingsurfaces at the wheels and the pivot points. The grounding practiceshould also avoid the reliance on travelling crane rails for grounding.

_ A grounding conductor within the trailing cable serving the crane or atrolley wire for grounding is the preferred method of grounding.

Portable Equipment

The following grounding requirements for Portable Equipment are found in SAES-P-111 andSADP-P-111:

_ Portable equipment includes electrical equipment that can bemanhandled and vehicle and skid-mounted equipment. Completeelectrical systems such as mobile flood-lighting plants, specializedvehicles, and other such vehicles that are confined to one vehicle,enclosure, or frame are excluded from consideration. Grounding to theearth may also be required to prevent static charges.

The following articles of the NEC apply to portable equipment havingelectrical power connections:

250-6 Portable and Vehicle Mounted Generators

250-45Equipment Connected by Cord and Plug




Portable Equipment (Cont'd)

250-59 Cord - and Plug - Connected Equipment

250-154 Grounding of systems supplying portable equipment (1 kV andover)

_ All portable equipment requires grounding except for certain lowvoltage or double insulated items.

_ Portable equipment, 600V and below:

_ A metallic connection must exist from all equipment to thesystem neutral. The grounding connection from the portableequipment will usually consist of a grounding conductor runwith the power supply conductors in a cable assembly or flexiblecord. Vehicle and skid-mounted equipment that is installed at alocation that has a suitable accessible grounding conductor musthave a temporary grounding connection placed between theequipment and the existing grounding conductor. This ground isin addition to any grounding conductor running with the powersupply cables.

_ Portable equipment, above 600 V:

_ The requirements of Section 250-154 of the National ElectricalCode apply for utilization equipment. These requirementsinclude the following:

_ An impedance grounded supply system.

_ Equipment grounding connection to the system neutralgrounding point.

_ Ground fault protection and monitoring of the continuity of thegrounding conductor.

_ System grounding electrodes must be separated from any otherelectrodes by a minimum distance of 6 m (20 ft).




Portable Equipment (Cont'd)

- When the requirements of Section 250-154 cannot be satisfied, theequipment must be immobilized and grounded in the same function asthe equivalent stationary equipment.

- Generation and distribution equipment must be immobilized andgrounded in the same fashion as equivalent stationary equipment.

- All portable equipment grounded in the same fashion as equivalentstationary equipment must have a minimum of two groundingconductors in parallel between the equipment and the ground grid,ground bus, or other grounding electrode. These conductors must bephysically separated and either removed from or protected from sourcesof mechanical damage.

Example of Mobile Equipment Grounding

Assume that a mobile diesel generator has been purchased and that the groundingrequirements for the mobile diesel generator must be established. The unit is mounted on atruck and can produce 200 kW of electrical power at an output of 277/480V, three-phase.

The frame of this vehicle can serve as the grounding electrode if the following conditions arein place:

_ The frame of the generator is bonded to the vehicle frame.

_ The noncurrent-carrying metal parts of the equipment and theequipment grounding conductor terminals of the receptacles are bondedto the generator frames.

_ The system complies with all other provisions of NEC Article 250.




DETERMINING THE BUILDING AND STRUCTURE GROUNDINGREQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS

The following is a list of applicable codes and standards that apply to Saudi Aramco buildingsand structures:

SAES-P-111 Grounding

SADP-P-111 Grounding

AA-036572 Drawing, "Grounding Arrangement for 115 kV DisconnectSwitch Structure"

AB-036562 Drawing, "Standard Switch Operating Platform"

SAES-O-101 Standard Security Fence

SAES-P-100 Basic Criteria

SAES-P-119 Substations

SAES-T Series Communications Standards

IEEE 80 Guide for Safety in Alternating-Current Substation Grounding

IEEE 81 Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System

IEEE 142 Recommended Practice for Grounding of Industrial and Commercial Power Systems

IEEE 367 Guide for Determining the Maximum Electric Power Station Ground Potential Rise and Induced Voltage from a Power Fault

NFPA 76A Essential Electrical Systems for Health Care Facilities

NFPA 76B Electricity in Patient Care Areas of Hospitals

NFPA 78 Lightning Protection Code




DETERMINING THE BUILDING AND STRUCTURE GROUNDINGREQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS (CONT'D)

This section will familiarize the Participants with the application of the basic safety codes todifferent facilities. This section includes the more important aspects of safety grounding forthe following types of buildings and structures:

_ Residential Building_ Industrial Building_ Manned Structures_ Unmanned Structures

Residential Building

Grounding for residential buildings starts with the system grounding at the servicedisconnect(s). Ground wires are then run from the main service panel, with the powerconductors, to the equipment or the electrical outlets. System grounding is normallyaccomplished through connection of the grounded conductor and the grounding conductor tothe grounding electrode conductor. In the case of small residential buildings, the groundingelectrode conductor often consists of underground metal piping and building steel. Groundloops for grids are seldom required for residential buildings.

Industrial Building

An industrial building is a facility in which products are manufactured or stored.

Industrial buildings are usually part of a complex with large power requirements. Substationgrid grounding, building ground loops, and an extensive system of ground conductors that tieall necessary items back to their respective power source are used.

Manned Structures

Manned structures are facilities that are occupied during normal business hours or on a 24-hour basis.

Manned structures are grounded in the same manner as industrial buildings.

Unmanned Structures

An unmanned structure is a building that is not occupied during normal business hours.Examples of unmanned structures are pumping stations and water treatment plants. The samegrounding rules apply to unmanned structures and to manned structures.




DETERMINING THE LIGHTNING PROTECTION REQUIREMENTS FOR SAUDIARAMCO INSTALLATIONS

This section will familiarize the Engineer with the hazards to life and to equipment that arecreated by lightning, as well as the grounding methods used at Saudi Aramco to reduce thedangers. This section includes the following information:

_ Nature of Lightning_ Equipment and Structures to be Considered_ Requirements for Good Protection_ Practices for Lightning Protection

Nature of Lightning

Lightning is the discharge of high-potential cells (usually negative) between clouds or from acloud to the earth. These charged cells normally attract the charges of opposite polarity onthe surface of the earth or on high objects. When the charge reaches a critical level (when theair insulation between the cloud and the earth breaks down), the charge develops a steppedionized path, resulting in a high current discharge (stroke) that neutralizes the cloud chargeand earth charge. The discharge current increases from zero to a maximum in 1 to 10 _s, thendeclines to half the peak value in 20 to 1000 _s. This discharge can be repeated one or moretimes over the same path, in rapid succession, because of the recharging in the cloud. Theaverage peak stroke current is about 20,000 A, although some peak stroke currents are asgreat as 27,000 A.

SAES-P-111 assists the Electrical Engineer in deciding when to protect or when not to protecta building or structure from lightning. Specifically, SAES-P-111 provides information onhow to determine the "Risk Index."

The Risk Index Tables are in Work Aid 6. Each table has a list of conditions. The ElectricalEngineer selects the condition that is correct for the building or structure that is beingconsidered for lightning protection and then records the risk figure for that condition. Oncethe risk figure for all seven tables has been determined, the Electrical Engineer sums theseven risk figures. The total is known as the Risk Index. If the Risk Index is 40 or greater,lightning protection must be provided.




DETERMINING THE LIGHTNING PROTECTION REQUIREMENTS FOR SAUDIARAMCO INSTALLATIONS (CONT'D)

The seven tables provided in Work Aid 6 are as follows:

_ Table 1 - Usage of Structure_ Table 2 - Type of Construction_ Table 3 - Contents of Structure_ Table 4 - Degree of Isolation_ Table 5 - Type of County_ Table 6 - Height of Structure_ Table 7 - Lightning Prevalence

Equipment and Structures to be Considered

The following buildings and structures should always be provided with a satisfactorylightning protective system:

_ Buildings and structures over 30 m (100 ft) in height.

_ Schools

_ Hospitals

_ Buildings and structures where the "Risk Index" is 40 or greater.

Equipment and structures can be separated into five classifications according to the need forlightning protection. These classifications are listed in IEEE Standard 142 and are as follows:

_ First Class_ Second Class_ Third Class_ Fourth Class_ Fifth Class

First Class

First class equipment and structures need very little or no additional protection. This classincludes the following:




Equipment and Structures to be Considered (Cont'd)

_ All metal structures except tanks or other enclosures of flammablematerials.

_ Water tanks, silos, and similar structures that are largely constructed ofmetal.

_ Flagpoles made of conductive material.

The only real requirement for this class is to connect the equipment or structure to a suitablegrounding electrode.

A typical Saudi Aramco example of first class equipment or structure would be a water tank.

Second Class

Second class equipment and structures consist of buildings with conducting surfaces and non-conducting framework, such as metal-roofed and metal-clad buildings. This class requires theaddition of down conductors to connect the exterior roof and cladding to suitable groundingelectrodes.

A typical Saudi Aramco example of a second class structure would be a chemical storagebuilding.

Third Class

Third class equipment and structures consist of metal-framed buildings with nonconductingfacings. These buildings need the addition of conducting air terminals that are suitablylocated and connected to the frame. The conducting air terminals must project beyond andabove the facing in order to act as the lightning terminal points and to thus eliminate thepotential of a puncture of the facing.

Chemical processes are often housed in this type of structure and are an example of the thirdclass structures at Saudi Aramco.

Fourth Class

Fourth class equipment and structures consist of non-metallic structures, either framing orfacing. These structures require extensive protection treatment. The following are examplesof fourth class structures:




Equipment and Structures to be Considered (Cont'd)

_ Buildings that are constructed of wood, stone, brick, tile, or othernonconducting materials and that are without metal reinforcingmembers.

_ High stacks and chimneys. Even with reinforcing members, thesestacks and chimneys should have full lightning protection treatment ofair terminals, down conductors, and grounding electrodes.

An example of this class at Saudi Aramco includes the stacks for boilers.

Fifth Class

Fifth class equipment and structures consist of items of high risk or loss consequences thatnormally receive full lightning protection treatment, including air terminals or diverters, downconductors, and grounding electrodes. This class includes the following:

_ Buildings of great aesthetic, historical, or intrinsic value.

_ Buildings containing readily combustible or explosive materials.

_ Structures containing substances that would be dangerous if released bythe effects of a lightning stroke.

_ Tanks and tank farms.

_ Power plants and water pumping stations.

_ Transmission lines.

_ ower stations and substations.

There are many examples of this class at Saudi Aramco.




Requirements for Good Protection

Direct lightning protection (lightning protection systems) consists of placement of airterminals at the top perimeter of the structure to be protected, and connection of the airterminals by adequate down conductors to the grounding electrodes (earth). The downconductor should not include any high-resistance or high-reactance portions or connectionsand should present the least possible impedance to earth without sharp bends or loops. Steel-framed structures, which are adequately grounded, meet these requirements with only theprovision for terminating the stroke on a metallic air terminal. The metallic air terminal isconnected to the frame structure, to avoid the possibility of puncturing any roofing or sidingto reach the frame. In the absence of a steel framework, a down conductor providing at leasttwo paths to earth for a lightning strike to any air terminal is generally adequate.

Air terminals that are attached to the structure itself are pointed solid rods or pipes at least 10inches (0.25m) long to possibly 2 feet (0.61m) long. On building edges, 10 inches (0.25m)terminals should not be separated by more than 20 feet (6.1m), and 2 ft. (0.61m) terminalsshould not be separated by more than 25 feet. (7.6m). Fifty feet (15.2m) of spacing willsuffice within the periphery.

At least two down conductors should be provided on all structures; only one down conductoris needed for masts, spires, and flagpoles. The greater the number of down conductors andgrounding electrodes, the lower the voltage that will be developed within the protectionsystem, and the better the protection. Every down conductor must be connected, at its base,to an earthing or grounding electrode. This grounding electrode should be within 2 feet(0.61m) of the base of the building and should extend below the building foundation, ifpossible.

Interior metal parts of a non-metal-framed building within 6 feet (1.83m) of a down conductorshould be connected to the down conductor. Exterior emergency ladders should also bebonded to the nearest down conductor. On a flat-top building protected by air terminals, allmetallic parts and equipment that are projecting higher than the air terminals (such as air-conditioning equipment) should be bonded to the lightning protection system. For high-risebuildings and towers, an equalizing horizontal bonding loop should be installedapproximately every 100 feet (30m).




Requirements for Good Protection (Cont'd)

Component Parts of a Lightning Protection System

SAES-P-111 and SADP-P-111 provide detailed information on the components of a lightningprotection system. The principle components of the lightning protection system are asfollows:

_ Air Terminals_ Down Conductors_ Joints and Bonds_ Ground Terminations

Air Terminals - NFPA 78 contains detailed information on air terminal design andsupport. No part of a flat or gently sloping roof on structures is to be more than 7.5 m(25 ft) from the nearest horizontal conductor.

Down Conductors - Two or more down conductors must be provided on most kinds ofstructures. One down conductor is permitted for flag poles, masts, spires or similarstructures. The total number of down conductors on structures having a flat or gentlysloping roof, and on irregular shaped structures are to be such that the average distancebetween the down conductors does not exceed 30 m (100 ft).

The bend in a conductor that embraces a portion of a building, such as an eave, musthave a radius that is greater than 200 mm (8 in). The angle of any turn must notexceed 90o, and the conductors must preserve a downward or horizontal course.

Enforcing rods that are butt-welded together are acceptable as down conductors, butreinforcing rods that are overlapped and bound with tye-wire are not acceptable asdown conductors.

Down conductors should be installed within the building or the structure to avoid thepotential "removal for gain" that can occur with external copper conductors. In orderto prevent lightning from "jumping" off the down conductor and to the conduit, downconductors must not be installed inside a metallic conduit.

Joints and Bonds - Joints and bonds must be made to the same standard as required forelectrical installations.




Requirements for Good Protection (Cont'd)

Grounding Terminations - The earth resistance of all lightning protection groundingterminations must be tested through use of an earth tester that is to be clamped to anyconvenient part of the lightning protective system. The combined resistance to earthof the whole of the lightning protection system must be as low as economicallypossible but must not exceed 25 ohms. Other grounds, such as substation grids orconsumer grounding, must be bonded to the lightning protection grounds. The intentof the grounding is to minimize the risk that is due to differential voltages that couldcause hazards to personnel or "sideflash" possibilities. Reinforcing rods in reinforcedconcrete foundations are not required to be bonded to the ground termination.

Practices for Lightning Protection

IEEE Standard 142, Section 3.3.4 provides the practices for lightning protection. Thisinformation is divided into the following seven (7) sections:

_ General_ Tanks and Tank Farms_ Non-Conducting Heavy-Duty Stacks_ Steeples_ High Masts_ Power Stations and Substations_ Communication Towers

General

Buildings and structures involving hazardous liquids, gases, or explosives require additionalprotection. In these buildings and structures, the object of the additional protection is to keepthe current away from the structure without use of the building's metal skin or the frameworkas a down conductor. A separate diverter protection system is employed for these buildingsand structures (e.g., tanks, tank farms, and explosive manufacture and storage).




Practices for Lightning Protection (Cont'd)

The diverter element consists of one or more masts, or one or more elevated wires (betweenmasts or poles), that meet the requirements of lightning protection. The masts or poles arenormally at least 10 feet (3m) from any part of the structure to be protected. Similarly,elevated wires that are above the structure must remain not less than 10 feet (3m) above thestructure. Metal masts can act as grounding conductors. Wood poles should have an airterminal securely mounted to the top of the pole. Copper or copper-weld conductor should beprovided along the pole as a grounding conductor. The guy wires for an elevated wire spancan be designed to serve as grounding conductors. Suitable earthing electrodes are necessary,as with all other types of grounding conductors.

Tanks and Tank Farms

Provided that the base of the tank is adequately grounded, a tank that contains flammableliquids or gases does not always need to be protected against lightning. Direct lightningstrikes to the tank top or walls are permitted as long as the steel is thicker than 3/16 inches(0.476cm). These strikes are allowed because there is little danger of the lightning strikespuncturing the tank. Steel tanks with steel roofs and floating metal roofs are generallyconsidered to be self-protecting. Tanks with nonmetallic roofs are not self-protecting andshould be protected with air terminals, conducting masts, or elevated ground wires. In allcases, joints and piping connections should be electrically continuous. All vapor or gasopenings should be closed or flame-proof. The possibility of a direct strike to the vicinity of avent or leak is eliminated by an air terminal of suitable length.

Refer to the Addendum, Saudi Aramco Drawing AB-036387, for grounding of floating tanks.

Non-Conduction Heavy-Duty Stacks

Heavy-duty stacks (including stacks in petroleum and in chemical plants) require air terminalsthat are connected to a loop conductor around the top of the stack and at least two downconductors that are connected to grounding electrodes at the base of the stack. Air terminalsshould be made of solid copper or stainless steel and should be uniformly distributed aroundthe top of cylindrical stacks, at intervals not exceeding 8 feet (2.44m). On square orrectangular stacks, air terminals should be located not more than 2 feet (0.61m) from thecorners and should be spaced not more than 8 feet (2.44m) apart around the perimeter.





The length of the terminals for nonflammable stack gas may be as little as 18 inches (0.46m).The length of the air terminals for ventilating stacks that emit explosive gas or dust should benot less than 5 feet (1.52m). The length of the air terminal where the gas or dust is explosiveand under forced draft should be not less than 15 feet (4.57m). Also, the terminals should betilted outward at 30o from the vertical. When the effluent is corrosive, as in flue gas, a 1/16inch (1.6mm) thick lead coating on the air terminal is required. The loop is also kept belowthe top of the stack.

Steeples

Steeples are similar to stacks except that they are sharp peaked and thus require only one airterminal. This one air terminal should project far enough above the top ornamentation tomeet the requirements of lightning protection. Otherwise, multiple air terminals or amultipointed terminal should be used to provide equivalent protection. Steeples arefrequently framed with wood, not metal, so adequate down conductors are a basicrequirement.

High Masts

Equipment on the sides of very high masts, such as television or FM antennas, can beprotected from direct stroke damage through the addition of lateral spikes or thorns projectingoutward from the sides of the mast. At heights above the critical radius of 100 or 200 feet (30or 60m), spikes in a horizontal or near horizontal position with suitable spacing will causestrokes coming from the side to terminate on the spikes rather than on the mast itself. Thispractice will greatly reduce the possibility of damage to electrically fragile components by thetermination of the lightning stroke arc. The number of spikes around the mast (three, four,five, or six), the length of the spikes, the vertical spacing along the mast need to bedetermined for optimum economics, and in accordance with the principles of lightningprotection. When masts are installed on top of a building, the bottom of the mast structuremust be bonded to the building grounding network at a minimum of two points.

Power Stations and Substations

While transmission-line protection against lightning is an inherent part of the design and iswell documented, the protection of stations and substations has received little attention.Lower stations and substations require protection from direct strokes. Masts or overheadwires (or both) can be used to ground lower stations and substations to the grounding networkof the power station or substation.





Protection of the attached overhead lines by means of an overhead grounded conductor ordiverter (static wire) for 2000 feet (610m) away from the station or substation isrecommended to preclude direct strokes on this section of the line and to reduce the duty onthe station surge arresters. The spacing of this overhead grounded conductor or diverter andthe associated down conductors from the phase conductors must not be less than the basicimpulse insulation level of the lightning protection system. Otherwise, side flashes to thephase conductors will occur and cause unnecessary outages. The installation of overheadgrounded conductors is not practical unless the attached overhead lines are 66 kV or above.

Communication Towers

SAES-P-111 and SADP-P-111 provide the following specific information on lightningprotection for communication towers:

_ Communication towers must be grounded by two 35 mm2 (No. 2AWG) conductors from points on diagonally opposite tower legs.These conductors are to run as directly as possible, but preferably byseparate routes, to the ground grid or other grounding electrode.

_ Towers at transmission substations or industrial complexes are tolocated within the resistance area of the installation either by proximityor by suitable configuration of the buried grounding conductors.

_ Towers in remote locations will require a grounding electrode. Thiselectrode is not to exceed 2 ohms of ground resistance. Ground rodswill suffice in areas of low soil resistivity; otherwise, a ground grid is tobe installed. Unless a power system that utilizes the ground gridrequires a larger conductor, a 35 mm2 (No. 2 AWG) conductor is to beused for the grid.




DETERMINING THE STATIC GROUNDING REQUIREMENTS FOR SAUDIARAMCO INSTALLATIONS

This section will discuss the hazards that static electricity can create and the methods that areavailable to eliminate these hazards. Specifically, the following topics will be discussed:

_ Causes of Static Electricity_ Conditions for Buildup of Static Electricity_ Hazards of Static Electricity and Control in Various Areas

Causes of Static Electricity

Static electricity is generated by the movement of electrons that occur when unlike materialsare in contact with each other and are then separated. When two unlike materials are inintimate contact, electrons from one material move across the interface to the surface of theother material. The protons remain on the original material. When the materials areseparated, electrical charges are produced on the materials.

If the two materials are good conductors, the excess electrons will easily flow back to thematerial with the positive charge, and there will not be a static electricity discharge. But, ifeither or both of the materials are insulators and are not grounded, some of the excesselectrons will be entrapped when the separation occurs, and the materials will be charged withstatic electricity.

The potential of the static electrical charge is related directly to the amount of charge that isdeposited on the material and is inversely proportional to the capacitance of this material.The relationship is expressed by the following equation:

where:

V = potential, in VoltsQ = chargeC = capacitance in farads




Causes of Static Electricity (Cont'd)

The developed potential can continue to grow if there is continuous charge generation. Atsome voltage level, the leakage current will equal the rate at which the charge is beinggenerated, and a stabilized condition will be reached. If the sparking potential is reached,sparking will occur.

Static electricity can be generated in the following situations:

_ Pulverized materials passing through chutes or pneumatic conveyors.

_ Belt drives that use belts of non-conductive material.

_ Gas, steam, or air flowing through an opening.

_ Motion that involves changes in the relative position of contactingsurfaces.

_ The human body in a low-humidity area. This generation can occur as aresult of the contact of shoes with floor coverings or by personnelworking near machinery that generates static electricity.

Conditions for Buildup of Static Electricity

The possibility that static electricity will be produced and the rate at which static electricitywill be produced depends on the following:

_ Material Characteristics_ Speed of Separation_ Area in Contact_ Effect of Motion Between Substances_ Atmospheric Conditions

Material Characteristics

One of the materials or substances must have a higher insulating property than the othermaterial or substance to generate static electricity. The amount of static electricity that existsbetween two materials will be proportional to the difference between the dielectric constantsof the materials.




Conditions for Buildup of Static Electricity (Cont'd)

Speed of Separation

As the speed of separation of two substances is increased, the potential of the static electricityis increased.

Area in Contact

The area of the contact between the substances has a direct bearing on the amount of staticelectricity. A larger contact area allows a greater charge to be transferred from one substanceto the other. As the area in contact increases, the potential of the static electricity increases.

Effect of Motion Between Substances

Static electricity is often thought to be a property of friction. This misunderstanding occursbecause "rubbing" two materials together will cause static electricity. This static electricityoccurs because the seemingly smooth items actually have peaks. When the items are rubbedtogether, the area of contact is increased. Increased motion will increase the amount of staticelectricity.

Liquids that are sprayed from a nozzle can generate static electricity, and liquids in a tank thatare agitated (stirred) can generate static electricity. These static electrical charges are causedby the motion of the liquid against the stationary components. Another very good example ofstatic electricity that is increasing due to motion is a belt and pulley. As the speed of the beltincreases, the amount of static electricity increases.

Atmosphere Conditions

It is well known that humidity conditions are related to the production of static electricity. Ashumidity increases, the potential for static electricity decreases; therefore, the hazard of staticelectricity increases in an operation that requires controlled low-humidity conditions.

Hazards of Static Electricity and Control in Various Areas

The accumulation of static electricity on equipment, on materials being handled or processed,and on operating personnel introduces a potentially serious hazard in any area whereflammable liquids, gases, dusts, or fibers are present. The discharge of the static electricityfrom an object to ground or to another object can be the cause of a fire or an explosion if thedischarge takes place in the presence of readily flammable materials or combustible vapor andair mixtures.




Hazards of Static Electricity and Control in Various Areas (Cont'd)

The following parts of SAES-P-111 and SADP-P-111 provide direction on how to prevent thebuildup of a static electricity charge and the subsequent discharge:

_ Agitators, Stills and Similar Equipment_ Belts - Pulleys_ Pipelines - Manifolds_ Steel Equipment and Process Units_ Tank Cars - Loading Racks - Spur Tracks_ Tanks - Atmospheric_ Tanks - Floating Roof_ Tankers and Barges - Marine Facilities

Agitators, Stills and Similar Equipment

The requirements for preventing a static electrical charge from accumulating on agitators,stills and similar equipment and the subsequent discharge are found in SAES-P-111 andSADP-P-111, as follows:

_ Vessels resting on earth, rock and oil, concrete, or brick foundations, oron concrete or steel supports are adequately grounded to prevent theaccumulation of static electricity; no special grounding devices arerequired. However, where insulation exists between the vessel and thesupports, grounding must be provided.

Belts-Pulleys

Belts that are made of rubber, leather, or other insulating materials, that are running atmoderate or high speeds, generate considerable quantities of static electricity. Generationoccurs when the belt separates from the pulley. The charges will exist on the pulley(regardless of whether the pulley is conducting or nonconducting) as well as on the belt.

The requirements for preventing a static electrical charge from accumulating on belts andpulleys and the subsequent discharge are found in SAES-P-111 and SADP-P-111:

_ If the pulley is made of a conducting material, such as metal, the chargewill be dissipated through the shaft and bearing to ground and offer noignition hazard. Where the machinery frame is insulated, or, thebearings are composed of insulating materials such as nylon, provisionsfor bonding and grounding are required.





_ A conductive belt or a belt made conductive through use of beltdressings must be used to prevent the accumulation of static charge. Thebelt dressings must be renewed frequently to be considered reliable andeffective.

_ The use of flat belts in hazardous areas must be avoided. The risk ofstatic ignition from V-belts is negligible.

_ Static combs are ineffective in draining off the static electrical chargeand should not be used.

Pipelines-Manifolds

The requirements for preventing a static electrical charge from accumulating on pipelines-manifolds and the subsequent discharge are found in SAES-P-111 and SADP-P-111, asfollows:

_ Permanent bonds between the separate lines in the piping system orbetween piping systems must be provided at tank car racks and inbuildings where volatile materials are handled.

Steel Equipment and Process Units

The requirements for preventing a static electrical charge from accumulating on steelequipment and process units and the subsequent discharge are found in SAES-P-111 andSADP-P-111, as follows:

_ Process equipment, (mainly steel vessels resting on steel or concretestructures) is required to be adequately grounded to prevent theaccumulation of static charges.

_ Where electrical devices are installed on process equipment, groundingmust be provided in accordance with SAES-P-111 and NFPA 70(NEC).

Tank Cars-Loading Racks-Spur Tracks

The requirements for preventing a static electrical charge from accumulating on tank cars,loading racks and spur tracks and the subsequent discharge are found in SAES-P-111 andSADP-P-111, as follows:





_ Tank cars are considered to be adequately grounded through the rails toprevent any hazardous accumulation of static charges on the tank body.

_ Where a tank car is unloaded or where rack installations are unloaded, abond wire must be provided between the nearest rail and fill line or tothe rack structure. A number of fill pipes can be electrically connected,and a single bond wire from the group can be attached to the rail.

_ No additional bonding of the tank car is required because the car isadequately bonded to rails.

_ To prevent arcing where stray currents are likely to occur, the rails mustbe bonded to each other. This bond must be a conductor not smallerthan 25 mm2 (No. 4 AWG), and it must be an adequate ground.

_ Additional protection against stray currents must be provided throughinstallation of insulated pipe joints between the loading and unloadingfacilities and the connecting yard piping.

_ If the spur track is connected to a railroad equipped with rail-circuitsignal systems, the spur must be isolated by rail joints that are insulated.

Tanks-Atmospheric

The requirements for prevention of accumulation of a static electrical charge on atmospherictanks and for prevention of the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows:

_ The shells of petroleum product storage tanks must be grounded at aminimum of four points that are spaced equidistantly around the base ofthe tank. Each point must be bonded to the area ground grid or to aground rod. The resistance between the tank shell and remote earthmust not exceed 10 ohms.

Tanks-Floating Roof

The requirements for prevention of the accumulation of a static electrical charge on tanks witha floating roof and for prevention of the subsequent discharge are found in SAES-P-111 andSADP-P-111, as follows:





_ The roof seal must be maintained to provide a tight closure that reducesthe chance of a vapor ignition at the seal. The possibility of vaporignition at the seal must be further reduced by the installation of metallicshunt strips at each pantagraph hangar in the sealing mechanism fromthe roof to the tank shell. These metallic shunt strips must be spaced amaximum of 3m (10 ft.) apart and must be bolted to the sealing ring andto the roof per Standard Drawing AB-036387, which is located in theAddendum. The metallic shunt strips and the roof also must be bondedto the tank shell.

Tankers and Barges - Marine Facilities

The requirements for prevention of accumulation of a static electrical charge on tanks andbarges and for prevention of the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows:

_ Insulated flanges and insulation for gangplanks must be provided atmarine terminals where stray currents can enter a tanker or a barge viagangplanks or piping as follows:

_ Leakage from power systems where return circuits through the earth cancause currents to flow through nearby piping in contact with the earth.

_ Potentials generated by galvanic action through contact between pipingand certain types of soil.

_ From cathodic protection systems.

_ Separated bodies and insulated flanges can become electrostaticallycharged when the product flows through the loading arm or hose. Suchflanges must be bonded to the pier and/or ship piping. All metal on theshore side of the insulating flange must be electrically continuous andgrounded via the dock piping, and all metal on the ship side must beelectrically continuous and grounded via the ship piping.

_ Where cathodic protection is not provided, and where conductive hosesor metallic loading arms are used, insulating flanges must bepermanently installed between the loading hose and pier piping. Theseinsulating flanges will electrically insulate the ship from the pier piping.





_ Where cathodic protection is provided on submarine loading lines,insulating flanges must be provided on the shore end of the submarinelines. At least one joint of the loading hose must be certified by themanufacturer to be electrically nonconductive. Submarine lines usedfor crude or fuel oil cannot accumulate static charges on isolated flangesdue to high electrical conductivity of these oils. Two groundingconnections on separate platform legs must be provided for groundingbarges.

_ An insulated flange must have an insulated material between thestandard flange faces. Each flange bolt must be encompassed by aninsulating sleeve and must have insulating washers at both ends of thebolt.

_ Insulating gaskets, bushings and washers must be of a material that iselectrically nonconductive and nonhygroscopic on all surfaces. Flangeedges must be sealed with a 50 mm (2") wide polyethylene pipe wraptape.

_ Gangplanks must be insulated at the pier end or at the ship end or atboth ends. As an alternative, the gangplank can have an insulating jointbetween pier end and ship end. The insulation must be providedthrough use of rubber tires, rubber rollers, rubber mat or insulatingjoints similar to the method for use with insulating pipe flanges.




DETERMINING THE GROUNDING REQUIREMENTS FOR SAUDI ARAMCOOFFSHORE PLATFORMS

An offshore platform is a large structure with a deck-like construction on which the drill rig ofan oil or gas well is erected. This platform is supported by a number of steel jacket legs.

The following mandatory requirements for offshore platform grounding are listed in SaudiAramco Engineering Standard SAES-P-111:

_ Two or more of the steel platform legs must be used as the groundingelectrode. Where two or more platforms are connected by walkways,two insulated grounding conductors must be installed to interconnectthe grounding electrodes between each pair of connected platforms.

_ A ground bus with a minimum size of 120 sq. mm (4/O AWG) must beestablished in the main electrical room or area. Equipment and systemneutral grounds must be connected to this bus by grounding conductors.This bus must extend to the grounding electrode by two separateconductors that are each sized to carry the rated bus current.

_ Exposed grounding conductors must be covered by green PVC.Exposed connections and terminations must be thoroughly covered withbitumastic (No. 50 or equal) and then taped.

_ Grounding conductors must not be installed in conduit except whennecessary to protect the conductor against mechanical damage.

Saudi Aramco Design Standard SADP-P-111 provides the following additional guidelines foroffshore platform grounding:

_ A connection via grounding conductors should exist between allelectrical equipment required to be grounded, all system neutrals, andthe grounding electrode. Ground-fault currents should not rely on thestructure of the platform for a return path.

_ Conductors should be selected in accordance with SADP-P-111 Chapter3. A minimum size of 120 sq. mm (No. 4/0 AWG) should be used forground bus conductors. All outdoor conductors should be PVCinsulated and colored green (e.g., cable type TW).




DETERMINING THE GROUNDING REQUIREMENTS FOR SAUDI ARAMCOOFFSHORE PLATFORMS (CONT'D)

_ A ground bus should be established in the main electrical plant room orarea. Equipment and system neutral grounds should be connected tothis ground bus. From this ground bus, additional buses will extend tothe grounding electrode, (the platform steel jacket legs) and to all partshaving electrical equipment.

_ Upon completion, all grounding conductor connections andterminations should be thoroughly coated with bitumastic No. 50 or aproduct that is equivalent to bitumastic No. 50. Connections in PVCinsulated conductors should then be taped so that the tape overlaps thepoint at which the PVC insulation was removed to make the connection.




DETERMINING THE GROUNDING REQUIREMENTS FOR DIGITALEQUIPMENT USED AT SAUDI ARAMCO INSTALLATIONS

This section will cover the grounding of electronic equipment for both safety and theelimination of electrical noise from the system. The following publications providetechniques for grounding computers and related equipment in a safe and reliable manner:

_ IEEE Paper Number PCIC-91-11_ Grounding and Shielding in Facilities, Chapter 6 and 7

IEEE Paper Number PCIC-91-11

This paper discusses the problems that are encountered in the design of grounding systems fordigital systems that meet the requirements given in the National Electrical Code (NEC) and inthe equipment manufacturer's site planning manuals and installation instructions.Specifically, the paper describes an integrated grounding practice that can be followed by theequipment manufacturers, the engineering companies, and the construction companies.

The key to grounding digital systems is to minimize, over the range of signal frequencies inuse, the differences in ground potential between components in the system. One of theprimary means of meeting this goal is to provide an integrated grounding system that meetsthe requirements of the NEC and that minimizes the noise in the system.

The Addendum contains a copy of IEEE Paper Number PCIC-91-11, which provides adetailed discussion of the integrated grounding practices for digital systems.

Grounding and Shielding in Facilities Chapter 6 and 7

Chapter 6 of the text "Grounding and Shielding in Facilities" provides details on the followingtopics:

_ Interference - An Introduction_ Energy Storage in Electric Fields_ Energy Storage in Magnetic Fields_ Signal and Power Transfer_ Electrical Power and signal Transport_ Poynting's Vector_ Reflection of Energy at a Surface_ A New Look at Voltage_ Fields and Ground Planes_ Using Ground Planes_ The Measurement of Interference_ Passive Filters




Grounding and Shielding in Facilities Chapter 6 and 7 (Cont'd)

_ Power Filter Location_ Modes of Interference_ Differential Mode Receptacle Filtering_ Transient Protection_ Equipment Ground Current at Power Frequencies_ Conductive Emission Control at Power Frequencies_ Conduit and RF Processes

Chapter 7 of "Grounding and Shielding in Facilities" contains detailed information on thefollowing topics:

_ The Search for the Perfect Ground_ Shielding and Electric Field_ The Transformer in Buildings and Equipment_ Common-Mode Shielding in Transformers_ Differential-Mode Coupling_ High-Frequency Power Filtering_ Transformers Again_ Computer Floors_ Cellular Raised Floor Utilization in a High-Frequency Noise

Environment_ Ground Planes_ Lightning and Zero Signal Reference Grids and Planes_ The Issue of Ground Loops_ Power and the Ground Plane_ Fields Entering a Facility_ Shielded Room Multiple Grounding Problems_ LC Filters and Shielded Rooms_ Double (Nested) Walled Shielded Rooms_ The Magnetic Field Problem_ Internal Equipment_ Containing Radiation Inside a Screened Room_ Fiber Optics and Shielded Rooms_ The Role of Skin Effect_ Radiation from a Shielded Room_ The Aperture Problem in Shielded Rooms_ Narrow Apertures and Arrays_ Anechoic Shielded Rooms_ Shielded Buildings_ Electrostatic Discharge (ESD)_ The ESD Process_ ESD Best Practices




_ ESD Tests




WORK AID 1: SAUDI ARAMCO AND INDUSTRY STANDARDS APPLICABLETO EQUIPMENT GROUNDING

Saudi Aramco Engineering Standard

_ SAES-P-111 : Grounding

Saudi Aramco Design Practice

_ SADP-P-1111 : Grounding

IEEE Standards

_ IEEE STD 80-1986 : IEEE Guide for Safety in AC SubstationGrounding

_ IEEE STD 142-1982 : IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems.

National Electrical Code

_ Article 250




WORK AID 2: FORMULA AND TABLE OF WIRE SIZES AND AMPACITY

Section 1

Procedure, Table and Formula for Determining the Size of Copper Grounding Conductors forEquipment Connected Directly to the LV Side of a Transformer Without an InterveningProtection Device, for Systems Rated 600V and Below.

1. Obtain the kVA rating of the power source transformer whose secondary is directlyconnected to the equipment without an intervening protection device, through us of thetransformer nameplate or the following formula:

where: V = System VoltageI = Current

2. Determine the type of protection (fuses or circuit breaker) provided for the primaryside of the power source transformer. This determination can be made through the useof personal knowledge of the system, electrical drawings, or a visual inspection.

3. Determine the size of the copper grounding conductor needed from the table ofGround Conductor Sizes shown in Figure 14, through the use of the kVA ratingobtained in step 1, and the type of protection determined in step 2.




Table of Ground Conductor SizesFigure 14

Section 2

Procedure and Table for Determining the Size of Equipment Grounding Conductors forEquipment Beyond the Main Switchboard or the Transformer Output Protection Device, forSystems Rated 600V and Below.

1. Determine the rating of the automatic overcurrent protection device in the circuit thatis ahead of the equipment. This determination can be made through the use ofpersonal knowledge, electrical drawings, or a visual inspection.

2. Determine the size of the equipment grounding conductor needed from Table 250-95of the NEC (shown in Figure 15) through use of the automatic overcurrent protectiondevice rating determined in step 1.




WORK AID 2 (Cont'd)

Table 250-95Figure 15




WORK AID 2 (Cont'd)

Section 3

Table, Formula, and Procedure for Determining Grounding Conductor Sizes in SolidlyGrounded Systems Over 600V.

1. Determine the three second short-time current capability of the circuit breaker ahead ofthe grounding conductors. This determination can be made through use of personalknowledge, the circuit breaker nameplate, electrical drawing, or the following formula:

Note: The formula must be used in cases where circuit breakers are not installed or wherethree second short-time capabilities are not assigned.

2. Determine the size of the grounding conductor needed from the table of groundingconductor sizes for solidly grounded systems over 600V (shown in Figure 16) throughuse of the three second short-time current capability determined in step 1.

Grounding Conductor Size for Solidly Grounded systems Over 600VFigure 16




WORK AID 2 (Cont'd)

Section 4

Table and Procedure for Determining Grounding Conductor Sizes in Impedance GroundedSystems Over 600V.

1. Answer the following question to determine the basis for the size of the groundingconductor in question.

2. Determine the 10 second current rating of the neutral grounding device or the 10second current rating of the combined neutral grounding devices for systems withmultiple neutral grounding devices connected in parallel. This determination can bemade through use of personal knowledge, the circuit breaker nameplate, or electricaldrawings.

3. Determine the size of the grounding conductor needed from the table of groundingconductor sizes for impedance grounded systems over 600V shown in Figure 17,through use of the current rating determined in step 2.




Grounding Conductor Size for Impedance Grounded System Over 600VFigure 17




WORK AID 3: FORMULA TO DETERMINE CONDUCTOR SIZE ANDREFERENCES FOR DETERMINING STATIONARY EQUIPMENTGROUNDING REQUIREMENTS

Use the following formula to calculate equipment ground conductor sizes for systems over600V.

where: tc = 3 seconds

ar = 0.00393 @20oC for soft drawn copper

pr = 1.7241 _ohm-cm @ 20oC

ko = 234 inverse of thermal coeff of resistivity 0oC

TCAP = 3.422 j/cm3/oC

Tm = 1083oC (fusing temperature of copper)

Ta = 40oC (ambient temperature)

I = RMS current in kA

For stationary equipment grounding requirements the Engineer should refer to Saudi AramcoEngineering Standard SAES-P-111-6 and Design Practice SADP-P-111 Chapter 3 & 6.




WORK AID 4: FORMULA TO DETERMINE CONDUCTOR SIZE ANDREFERENCES FOR DETERMINING MOBILE EQUIPMENTGROUNDING REQUIREMENTS

Use the following formula to calculate equipment and systems neutral ground conductor sizesfor systems over 600V or for impedance grounded systems where short circuit levels exceeds12 kA.

where: tc = 3 seconds

ar = 0.00393 @20oC for soft drawn copper

pr = 1.7241 _ohm-cm @ 20oC

ko = 234 inverse of thermal coeff of resistivity 0oC

TCAP = 3.422 j/cm3/oC

Tm = 1083oC (fusing temperature of copper)

Ta = 40oC (ambient temperature)

I = RMS current in kA

For mobile equipment grounding requirements, the Engineer should refer to Saudi Aramcodesign practice SADP-P-111 Chapters 3 and 6 as well as Article 250 NEC.




WORK AID 5: REFERENCES FOR DETERMINING BUILDING ANDSTRUCTURE GROUNDING REQUIREMENTS

NEC Article 250: Grounding

Saudi Aramco Design Practice SADP-P-111, Chapters 3 and 6.




WORK AID 6: REFERENCES FOR DETERMINING LIGHTNING PROTECTIONREQUIREMENTS AND TABLES FOR CALCULATING RISKINDEX

Saudi Aramco Design Practice SADP-P-111, Chapter 9, Lightning Protection of Buildingsand Structures.

"Risk Index"

To assist in deciding "when to protect or when not to protect" a building or structure againstlightning a "Risk Index" must be determined. For a specific application the summation of allthe relevant risk figures from Table 1 to 7 inclusive provides the "Risk Index".

When the "Risk Index" totals 40 or greater lightning protection must always be provided.

TABLE 1 - USAGE OF STRUCTURE Risk Figure

Houses and other buildings of comparable size 2with outside aerial .. .. .. .. .. .. 4

Factories, workshops and laboratories .. .. .. 6Office blocks, hotels, blocks of flats and

other residential buildings other thanthose included below .. .. .. .. .. .. 7

Places of assembly, e.g. halls, theaters,museums, exhibitions, department stores,post offices, airports, and stadiumstructures .. .. .. .. .. .. .. .. .. 8

Schools, hospitals .. .. .. .. .. .. .. .. .. 10




WORK AID 6 (Cont'd)

TABLE 2 - TYPE OF CONSTRUCTION Risk Figure

Steel framed encased, with any roof otherthan metal + .. .. .. .. .. .. .. .. 1

Reinforced concrete with any roof otherthan metal .. .. .. .. .. .. .. .. .. 2

Brick, plain concrete or masonry with anyroof other than metal .. .. .. .. .. .. 4

Steel framed encased or reinforced concretewith metal roof .. .. .. .. .. .. .. .. 5

Timber framed or clad with any roof otherthan metal .. .. .. .. .. .. .. .. .. 7

Brick, plain concrete, masonry, timberframed but with metal roofing .. .. .. .. .. 8

+ A structure of exposed metal which is continuous down to ground level is excludedfrom the tables as it requires no lightning protection beyond adequate groundingarrangements.

TABLE 3 - CONTENTS OF STRUCTURE

Ordinary domestic or office buildings,factories and workshops not containingvaluable or specially susceptiblecontents .. .. .. .. .. .. .. .. .. .. 2

Industrial buildings with speciallysusceptible contents + .. .. .. .. .. .. .. 5

Power stations, gas works, telephoneexchanges, radio stations .. .. .. .. .. 6

Industrial key plants, museums, artgalleries or other buildings withspecially valuable contents .. .. .. .. 8

Schools, hospital, places of assembly 10

+ Indicates items of particular value ormaterials vulnerable to fire or theresults of fire.




WORK AID 6 Cont'd)

TABLE 4 - DEGREE OF ISOLATION Risk Figure

Structure located in a large area withstructures of the same or greater height(e.g., in a large town) .. .. .. .. .. 2

Structure located in an area with fewother structures of similar height.. .. 5

Structure completely isolated or exceedingat least twice the height of surroundingstructures .. .. .. .. .. .. .. .. 10

TABLE 5 - TYPE OF COUNTRY

Flat country at any level .. .. .. .. 2Hill country .. .. .. .. .. .. .. .. 6Mountain country between 300 m and 900 m

(1000 ft and 3000 ft) 8Mountain country above 900 m (30090 ft) .. 10

TABLE 6 - HEIGHT OF STRUCTURE

Exceeding Not Exceeding

9 m (30 ft) 2 9 m (30 ft) 15 m (50 ft) 415 m (50 ft) 18 m (60 ft) 518 m (60 ft) 24 m (80 ft) 824 m (80 ft) 30 m (100 ft) 11

Structures higher than 30 m (100 ft) requireprotection in all cases.

TABLE 7 - LIGHTNING PREVALENCE

Risk Figure for Arabian Conditions 10




WORK AID 7: REFERENCES FOR DETERMINING STATIC GROUNDINGREQUIREMENTS

This Work Aid is designed to help the Participants in performing Exercise 7.

_ SAES-P-111

_ SADP-P-111 Chapter 14

_ IEEE STD.142, Section 3




WORK AID 8: REFERENCES FOR DETERMINING OFFSHORE PLATFORMGROUNDING REQUIREMENTS


_ SAES-P-111_ SADP-P-111 Chapter 8




WORK AID 9: REFERENCES FOR DETERMINING DIGITAL EQUIPMENTGROUNDING REQUIREMENTS


_ IEEE Paper Number PCIC 91-11




GLOSSARY

dielectric constants The property that determines the electrostatic energy that is storedper unit volume for unit potential gradient.

effectively grounded Grounded through a grounding connection that has sufficiently lowimpedance (inherent or intentionally added or both) to prevent thebuildup of voltages in excess of limits that are established forapparatus, circuits, or systems so grounded, in the event a groundfault does occur.

equipment ground A ground connection to non-current carrying metal parts of a wiringinstallation, electric equipment, or both.

ground A conducting connection, whether intentional or accidental, bywhich an electric circuit or equipment is connected to the earth or tosome conducting body, of relatively large extent, which serves inplace of the earth.

ground bus A bus to which the grounds from individual pieces of equipment areconnected and that, in turn, is connected to ground at one or morepoints.

ground clamp A clamp that is used in connecting a grounding conductor to agrounding electrode or to something that is grounded.

ground conduit A conduit that is used solely to contain one or more groundingconductors.

ground current Current that is flowing in the earth or in a grounding connection.

ground detector An instrument or equipment that is used for indicating the presenceof a ground on an ungrounded system.

ground grid A system of grounding electrodes that consists of interconnectedbare cables buried in the earth to provide a common ground forelectric devices and metallic structures.

ground lug A lug that is used to connect a grounding conductor to a groundingelectrode or to something that is grounded.

ground-return circuit A circuit in which the earth is utilized to complete the circuit.




grounded Connected to earth or to some extended conducting body that servesinstead of the earth, whether the connection is intentional oraccidental.

grounded circuit A circuit in which one conductor or point (usually the neutralconductor or neutral point of transformer or generator windings) isintentionally grounded, either solidly or through a grounding device.

grounded concentric A grounded system in which the external (outer) conductor is solidlywiring system grounded and that completely surrounds the internal (inner)

conductorthroughout its length. The external conductor must be jacketed.

grounded conductor A conductor that is intentionally grounded, either solidly or throughacurrent limiting device.

grounded electrode A conductor used to establish a ground: for instance, ground grids,ground rods, ground wells, etc.

grounded system A system of conductors in which at least one conductor or point(usually the middle wire or neutral point of transformer or generatorwindings) is intentionally grounded, either solidly or through acurrent limiting device.

grounding conductor The conductor that is used to establish a ground and that connects anequipment, device, wiring system, or another conductor (usually theneutral conductor) with the grounding electrode or electrodes.

grounding connection A connection that is used in establishing a ground and that consistsofa grounding conductor, a grounding electrode and the earth (soil)that surrounds the electrode.

grounding outlet An outlet that is equipped with a receptacle of the polarity type andthat has, in addition to the current-carrying contacts, one groundedcontact that can be used for the connection of an equipmentgrounding conductor.

grounding A transformer that is intended primarily to provide a neutral pointfor

transformer grounding purposes.




guard wire A grounded wire that is erected near a lower-voltage circuit orpublic crossing in such a position that a high (or higher) voltageoverhead conductor cannot come into accidental contact with thelower-voltage circuit, or with persons or objects on the crossingwithout first becoming grounded by contact with the guard wire.




impedance grounded Grounded through impedance.

neutral ground An intentional ground applied to the neutral conductor or neutralpoint of a circuit, transformer, machine, apparatus, or system.

reactance grounded Grounded through impedance, the principal element of which isreactance.

resistance grounded Grounded through impedance, the principal element of which isresistance.

solidly grounded Grounded through an adequately grounded connection in which noimpedance has been inserted intentionally.

system grounding An auxiliary solidly grounded conductor that connects the individualconductor grounding conductors in a given area.

ungrounded A system, circuit, or apparatus without a conducting body thatserves instead of the earth, whether the connection is intentional oraccidental.




ADDENDUM A

Saudi Aramco Drawing AB-036387 IEEE Paper PCIC-91-11