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Grounding and Overvoltage Protection IP 16-4-1

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THIS INFORMATION FOR AUTHORIZED COMPANY USE ONLYEXXON RESEARCH AND ENGINEERING COMPANY FLORHAM PARK, N.J.

INTERNATIONALPRACTICE

SCOPE

I 1.1 This practice covers bonding, grounding, overvoltage protection, and lightning protection facilities forelectrical power systems and equipment, structures and buildings, and product loading stations.

I 1.2 This practice does not cover process instrumentation systems. However, overall grounding system

design shall include requirements specified in other practices, e.g. instrumentation. Contractor shall submitoverall grounding design to the Owner's Engineer for approval.

I 1.3 An asterisk () indicates that additional information is required. If a job is contracted, this additional

information is furnished in the Job Specification.

SUMMARY OF ADDITIONAL REQUIREMENTS

I 2.1 Table 1 lists standards that shall be used with this practice. Equivalent regional or national standards may

be used when approved by the Owner's Engineer.

TABLE 1

STANDARDS

ANSI / NFPA

70 National Electrical Code (NEC) Article 250780 Standard for the Installation of Lightning Protection Systems

IEEE

837 IEEE Standard for Qualifying Permanent Connections Used in Substation Grounding

I 2.2 ANSI / IEEE Std 80, IEEE Guide for Safety in AC Substation Grounding shall be used as indicated in thispractice.

DEFINITIONS

I 3.1 Acceptable and preferred practices. Where this practice lists more than one type of equipment or method

as acceptable, the contractor shall make the selection based on the installed cost. Where one particulartype of equipment or method is listed as preferred, it shall be selected, provided: (1) it is lower or equivalentin installed cost than other acceptable types or methods, (2) it has reduced maintenance and operating coststhat provide sufficient cost benefit to offset an initial added investment. Owner's Engineer shall approvealternative choices.

I 3.2 Bonding. Two or more objects are considered to be bonded if connected together through a conducting

path. Objects which are not inherently in contact with each other through a conducting path may be bondedby connecting them together with a bonding conductor. The conductor shall be sized to safely conduct thecurrent or dissipate the charge likely to be imposed.

I 3.3 Grounding. An object is considered to be grounded when connected by a conducting connection either

inherently or by a grounding conductor to the earth, or to some conducting body that serves in place of theearth such as where rock or high resistivity soil is present.

I 3.4 Grounds are the grounding electrode system. The electrodes may be buried grounding conductors,

underground metallic water piping, large underground metallic objects in intimate contact with earth such asmetallic building frames, pile casings, or concrete encased electrodes consisting of reinforcing bars orcopper conductors in underground foundations or footings, and driven rods.

I 3.5 The zone of lightning protection is that space adjacent to a lightning protection system that is substantially

immune to direct lightning flashes.ANSI / NFPA 780 Chapter 3 Protection for Ordinary Structures" and Chapter 6 Protection for Structures

Containing Flammable Vapors, Flammable Gases or Liquids That Can Give Off Flammable Vapors" coverthe cone and rolling sphere concepts for determining the zone extent. Specific regional or nationalstandards, while using the same concepts, may have requirements that result in different extents of the zoneof protection.

I 3.6 Lightning arrester (surge arrester) is a protective device for limiting surge voltages on equipment by

discharging or bypassing surge current. It prevents continued flow of follow current to ground, and is capableof repeating these functions. Use of arcing horns and/or rod gaps is not an acceptable method ofsuppressing electrical surges.

Changes shown by

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IP 16-4-1 Grounding and Overvoltage ProtectionPage 2 of 11

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I 3.7 Liquids are classified as static electrical charge accumulators if their conductivity is 50 picomhos/meter

(50 pS/m) or less. Distilled petroleum products including petroleum solvents, are generally accumulators.Crude oil, residual fuel oil, asphalts (both penetration or cutback), Bunker C, residual products withConradson carbon above 1% and water soluble products such as alcohol have high conductivity and areclassified as non-accumulators.

I 3.8 Ground return path is a metallic connection between the metal enclosure of electrical equipment and thesystem neutral ground of the power supply to the equipment. If the systems neutral is grounded throughimpedance, the ground return path must connect on the ground side of the impedance. The path is a low-impedance path from the equipment enclosure to the neutral ground. It serves as the equipment groundingconductor in grounded neutral systems.

I 3.9 Switch loading is loading a high flash product into a tank truck, tank car, or container previously containinga low flash product, without cleaning or gas-freeing the tank or container. The high flash product must betreated as low flash during loading in such cases.

BONDING AND GROUNDING MATERIALS AND METHODS

S 4.1 Bonding shall be provided where necessary to insure the electrical continuity of grounding circuitsand where necessary to provide a path for the dissipation of static charges.

S 4.2 Bonds provided for the dissipation of static charges shall have a resistance of one megaohm or less.

BONDING AND GROUNDING CONDUCTORS

R 4.3 Unless otherwise specified, bonding and grounding conductors shall be bare stranded medium-hard-drawn copper. Minimum sizes shall be 2 Awg (35 mm2) for underground conductors and 6 Awg (16 mm2)for aboveground conductors where the size is not specified elsewhere in this practice. Conductor sizesshall be increased above the minimum sizes if required to:

a. Insure adequate mechanical strength.

b. Withstand the thermal stresses of ground fault currents.

R 4.4 Ground return conductors located within cable assemblies or run with or enclosing individual circuit

conductors are preferred. When specified, common ground return conductors run with undergroundconduits or buried cable are acceptable.

I 4.5 Ground return conductors located within cable assemblies may be uninsulated and shall be of the

same material and stranding as the cable line conductors. If insulated, color coding shall comply withrequirements of the applicable regulations.

R 4.6 Grounding conductor burial depths shall be at least 18 in. (450 mm). Burial depths in switch or

transformer yards graded with stone shall be at least 12 in. (300 mm) below the stone.

R 4.7 If the wiring method is buried cable, common grounding conductors run with the buried cable shall belaid in the cable trenches as far as routing permits.

R 4.8 If the wiring method is underground conduit, common grounding conductors run with the conduits shallbe laid along a formed side of the duct banks.

S 4.9 Grounding conductors leaving the ground at grade shall be protected as follows:

a. Conductors except those used for lightning protection and lightning arrester grounding shall be protectedby rigid metal or non-metallic conduit or pipe sleeves where they extend above grade. Lightningprotection and arrester ground conductors shall be protected by non-metallic conduit sleeves.

b. Sleeves shall extend a minimum of 6 in. (150 mm) below grade and 10 in. (250 mm) above grade.

c. Metal sleeves shall be encased in concrete 3 in. (75 mm) thick all around.

d. Concrete encasement shall extend 6 in. above grade.e. Non-metallic sleeves shall be rigid heavy wall polyvinyl chloride or high density polyethylene conduit.

f. Sleeves are not required within switch or transformer yards or under elevated substations.
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BONDING AND GROUNDING CONNECTIONS

S 4.10 All conductor connections to structures and equipment shall be made aboveground as follows:

a. Conductors shall be installed in one length between aboveground connection points.

b. Single cable lengths shall also be installed between aboveground connection points and groundingelectrodes or taps on common ground return cables.

c. If splices or taps are required on underground runs, they shall be made with tool-installed compressionconnectors or by brazing or welding.

d. Bolted or screw type solderless connectors or similar mechanical connectors shall not be usedunderground.

e. Splices or taps in underground runs shall be buried.

M 4.11 On equipment, conductor connections that are regularly disconnected for maintenance of theequipment shall be made with bolted or screw type solderless connectors. Other connections shall bemade by brazing, welding, or with connectors that qualify as permanent grounding connections perIEEE Std837.

GROUNDS

S 4.12 All Grounds shall have a resistance to earth not exceeding 5 ohms throughout the year consideringseasonal variations in soil conditions. Grounds for low resistance grounded systems shall not exceed 2ohms.

R 4.13 Grounding Electrodes. If permanently installed and located within a reasonable distance of the equipment

or structure to be grounded, the following may be used as grounding electrodes:

a. Buried grounding conductors having a length of not less than 20 ft (6 m) and burial depth of 30 in.(760 mm). Minimum size shall be No. 2 Awg (35 mm2).

b. Underground metallic water piping if buried portion is more than 10 ft (3 m) in length.

c. Large underground metallic objects in intimate contact with earth such as metallic building frames, pilecasings or concrete encased electrodes consisting of reinforcing bars or copper conductors that are partof an underground foundation or footing. These electrodes shall provide the conductive equivalent of atleast 20 ft (6 m) of electrically conductive reinforcing bar not less than 1/2 in. (13 mm) diameter or 20 ft(6 m) of No. 2 Awg (35 mm2) copper conductor. Concrete encasement shall not be less than 2 in. (50

mm) thickness. d. Artificial (made) electrodes consisting of driven copper-clad steel rods or equivalent. Unless specifiedotherwise, rods shall be copper-clad steel equivalent to Copperweld with minimum diameter of 5/8 in.(16 mm) and minimum length of 8 ft (2.5 m). Tops of rod and grounding conductor connection shall beburied at least 18 in. (450 mm) below grade. A ground well shall be provided for each rod and itsconnector when specified.

e. If more than one electrode is connected to a grounding system, the electrode spacing shall be spaced atleast 10 ft (3 m) apart.

f. Electrodes of different systems shall be bonded together when in reasonable proximity.

M 4.14 Electrode grounding conductor and connections shall comply with the following:

a. A grounding conductor shall connect the top of each electrode to an accessible above groundconnection point. Minimum size shall be No. 2 Awg (35 mm2).

b. The connection point may be located on the structure or equipment to be grounded or on a nearby

permanent structure to serve as a tie-in point for other grounding conductors. At tie-in points,conductors from electrodes shall be identified with corrosion resistant metal bands to facilitate theirremoval for test purposes.

c. The grounding conductor shall be connected to the electrode by brazing or welding, and to theconnection points by a bolted or screw type solderless connector. In ground wells the rod connectionmay use bolted or screw type connectors.

SUBSTATION AND GENERATING STATION GROUNDS

S 4.15 All grounding electrodes at substations and generating stations shall be interconnected by grounding

conductors.
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S 4.16 Design of grounding systems shall provide protection from step, touch, mesh and transfer potentials at

the following areas:

a. Outdoor switchyards and main substations that are supplied by overhead lines at utility companyvoltage.

b. Substations adjacent to a utility-supplied switchyard or main substation.

c. Generating stations.

d. Gas-insulated substations (GIS) Grounding system design shall be evaluated using the guidelines presented in ANSI / IEEE Std 80, or

equivalent regional or national standard. Grounding system design for these areas shall be submitted toOwner's Engineer for approval.

SYSTEM NEUTRAL GROUNDS

GROUNDING CONDUCTOR SIZE

R,O 5.1 Grounding conductors used to ground power transformer or generator neutrals shall have a cross

sectional size not less than 2 Awg (35 mm2). In addition, the size shall limit temperature reached by the

conductor, when carrying maximum ground fault current for the time allowed by the slowest responsiverelay, to the following:

a. For insulated conductors, to within the transient temperature for no damage to the insulation.

b. For bare conductors: to 250C rise if connections to cable are made with pressure connectors; to 450 C

rise if connections to cable are brazed or welded. For copper conductor and 26C ambient, required

size is: tIF

where: I = current, amp

t = time, seconds

F = 0.0106 for answer in kCM and 250C rise

= 0.0087 for answer in kCM and 450C rise

= 0.0054 for answer in mm2and 250C rise

= 0.0044 for answer in mm2and 450C rise

c. For impedance grounded systems, the grounding conductor ampacity for the time allowed by the lowestresponsive relay shall be not less than the maximum current rating of the impedance and the minimum

size specified by the applicable regulations.

GROUNDING CONDUCTOR ROUTING

I,R 5.2 For solidly grounded systems, the grounding conductor shall be routed as follows:

a. If the neutral grounding connection is made at a transformer or generator, or at an adjacent neutralcurrent transformer, the conductor shall be routed via the shortest path to ground. For transformers, theshortest path is usually via the transformer ground pad.

b. If the neutral ground connection is made in the transformer or generator switchgear, route the conductorto ground via the switchgear ground bus. All connections in the grounding path between the neutralpoint and the outdoor ground shall be accessible for visual inspection. When specified, the conductorshall be insulated between the neutral and the grounding point in the switchgear.

c. For grounded lighting systems having individual lighting transformers and panels, transformer neutralshall be grounded only at the transformer.

I,R 5.3 For impedance grounded systems, the neutral impedance element shall be located as close aspracticable to the neutral. The neutral grounding conductor should be routed from the impedance elementvia the shortest path to ground.
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GROUNDING CONDUCTOR INSULATION AND PROTECTION

S 5.4 For solidly grounded systems, the neutral grounding conductorshall be insulated for at least line-to-

neutral voltage where the conductor passes along or in the enclosure of electrical equipment. Specificallythis applies to:

a. Runs from transformer or generator terminal chamber or CT enclosure to transformer ground pad orgenerator grounding point.

b. Runs from transformer or generator neutrals to switchgear neutral bus or ground bus.

c. Runs from switchgear neutral bus to switchgear ground bus.

S 5.5 For impedance grounded systems, the connection between neutral and impedance must be insulated

for at least line-to-neutral voltage. Where required by regional or national standards, the connection shall beinsulated for phase-to-phase voltage.

I 5.6 Insulation color coding shall comply with requirements of the applicable regulations.

R 5.7 Protective conduits for neutral grounding conductors, if used, shall be rigid aluminum or non-metallic

conduit. Non-metallic conduit shall be heavy wall rigid polyvinyl chloride or high density polyethylene.

ENCLOSURE GROUNDING

WIRING SYSTEMS

S 6.1 Metal enclosures for wire and cable such as conduits, cable trays and raceways shall be grounded attheir supply ends by connection to the switchgear or control center ground bus, when such equipment isused; or by connection to the grounded metallic equipment enclosures when switchracks are used. The wireand cable metal enclosures shall be metallically connected to utilization equipment enclosures at their loadend.

S 6.2 The electrical continuity of metal enclosures or wire and cable shall be assured between terminations.Non metallic conduit sections or fittings shall not be used in metal conduit systems unless bonding isprovided across such section and fittings.

S 6.3 Metallic armor and sheaths, and metallic insulation shielding of all cables shall be bonded togetherand grounded at the cable's supply end by connection to the switchgear or control center ground bus,when such equipment is used; or by connection to the grounded metal equipment enclosures whenswitchracks are used.

S 6.4 Metallic armor and sheaths of multi-conductor cables shall be bonded and grounded per the following:a. Bonded together and grounded at each cable termination.

b. Bonded together at each splice and bonded across each splice.

c. Bonded together and to equipment metal enclosures at the load end.

R 6.5 Metallic insulation shielding in shielded multi-conductor cables shall be grounded at each terminationand shall be bonded to the cable metal sheath and armor (if any). If practicable, the insulation shielding ofcables with multiple splices, also shall be grounded at each splice and bonded to the cable metal sheathand armor (if any).

R 6.6 Single-conductor cables. Bonding and grounding methods for single-conductor cables havingmetallic armor, sheaths or insulation shielding must be engineered for the specific installation to avoid

dangerous sheath or shield voltages or excessive heating due to circulating currents. Generally, single-conductor cables smaller than 500 kCM (240 mm2) with all three phases in the same duct may be bondedand grounded the same as multi-conductor cables. Armor, sheaths, and shielding of larger cables may

require single point grounding with insulating joints between grounded sections.

EQUIPMENT

S 6.7 Metal enclosures of fixed equipment operating above 1000 volts between conductors shall begrounded by a connection to a ground in their immediate vicinity in addition to the ground return conductor.

S 6.8 Metal enclosures of fixed equipment operating at 1000 volts or less between conductors and suppliedfrom ungrounded or high resistance grounded systems shall be grounded by one of the conductor typesspecified in Par. 7.5.

C 6.9 If supplied from solidly grounded systems, metal enclosures of fixed equipment operating at 1000volts or less between conductors are considered grounded through their ground return path and do not

require further grounding.
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S 6.10 Main distribution equipment. Metal-clad and metal-enclosed switchgear, control centers andturnaround power centers shall be grounded by two separate connections from their ground busses togrounds in the immediate vicinity. The metal enclosures of the individual devices on switchracks shallbe bonded to the switchrack frame, and the frame shall be grounded by two separate connections togrounds in the immediate vicinity. Equipment grounds in substations of grounded neutral systems

shall be interconnected with the substation neutral ground.

S 6.11 Metal enclosures of portable equipment shall be connected to a grounding conductor located within

the same cable assembly as the line conductors supplying the equipment as follows:

a. Grounding conductor shall be the same size as the line conductor.

b. Grounding conductor shall be connected to the receptacle enclosure through separate contacts in thesupply plug and receptacle, and shall be bonded to the plug enclosure.

c. Plug and receptacle shall be polarized and arranged so that the ground connection makes first andbreaks last.

Note: For enclosed or confined conductive work spaces, applicable regulations may place specificrestrictions on grounding and power supply for portable equipment used in these spaces.

S 6.12 Metal enclosures such as fences, partitions, and grill work around equipment operating above 1000volts between conductors, shall be grounded by connections to grounds in their immediate vicinity.

S 6.13 Metal fences and grills enclosing the space under elevated substation buildings shall be grounded by

connections to ground in their immediate vicinity.

GROUND RESISTANCE

S 6.14 Grounds for enclosures shall have a resistance to earth not exceeding 15 ohms.

GROUND RETURNS

R,O 7.1 A ground return path is required for each circuit in the following:

a. Solidly grounded systems.

b. Impedance grounded systems.

R,O 7.2 If switchgear or control centers are used, the supply ends of ground return paths shall terminate at

the switchgear or control center ground bus.

R,O 7.3 If switchracks are used, the supply ends ofground return paths shall terminate by connection to the

metal enclosure of the individual control devices.R,O 7.4 The load ends of ground return paths shall terminate by connection to a ground bus, when available, or

to the metal enclosure of the equipment served by the ground path's circuit.

I 7.5 Ground return paths shall be one of the following:

a. Rigid metal conduit.

b. Wire or cable conductors run as a separate conductor or as part of a cable assembly.

c. Type MI cable copper sheaths.

d. Copper wire cable armor or other armor types acceptable under the applicable regulations.

e. Electrical metallic tubing, armor or sheaths of metal-clad cable used in circuits not more than 150 ft (45m) in length and protected by overcurrent devices having a nominal rating of 20 amperes or less.Length restrictions apply to solidly grounded and low resistance grounded systems.

f. Metal covered cable sheaths of circuits protected by ground fault relaying in solidly grounded and low

resistance grounded systems and provided that the sheath is capable of carrying the maximum groundfault current without damage (to the sheath or cable) for the time allowed by the slowest responsiverelay.

g. Metal-enclosed bus duct enclosures where bus duct length does not exceed 25 ft (7.5 m). Lengthrestrictions apply to solidly grounded and low resistance grounded systems.

h. Ground return paths using a combination of the paths listed are acceptable subject to approval of theOwner's Engineer.

R,O 7.6 For solidly grounded and low-resistance grounded systems the combined impedance of the groundreturn path and the supply circuit line conductors shall be low enough to insure operation of the circuitovercurrent protective device in less than 2 seconds on a single line-to-ground fault at the load end of thecircuit. An arc voltage of 40 volts in phase with the line-to-neutral source voltage shall be assumed at thefault point.
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GROUND RETURNS (Cont)

For receptacle circuits, the impedance of the plug connected portable cord shall be included in thecombined impedance used to check operation of the protective device. Maximum cord length of 100 ft(30 m) shall be assumed.

Notes:

(1) For circuits protected by ground relaying, circuit lengths established by voltage drop limits in normaloperation will generally result in ground return path impedances low enough to meet theserequirements.

(2) For circuits with phase protection only (not protected by ground relaying), normal circuit lengths mayresult in return path impedance too high to insure proper operation of the circuit overcurrent protectivedevices on ground faults.

GROUND RETURN THROUGH FLEXIBLE CONDUIT

R,O 7.7 Bonding jumpers shall be installed around flexible conduit connections used on solidly grounded andlow resistance grounded systems whenever a conductor ground return is not provided within the flexible

conduit.

CONDUCTOR GROUND RETURNS

R,O 7.8 Wire or cable conductors used as ground return paths in metallic or non-metallic conduit systems shallbe run within the same conduit as the circuit line conductors. The ground return conductors shall be

jacketed if not located within the line conductor assembly. Such conductors are required with non-metallic conduit systems. Generally such conductors are not required with rigid metal conduit systems butmay be used to increase maximum circuit length in rigid steel conduit systems.

C 7.9 When specified, one or more conductors may serve as the common (main) ground return path for agroup of circuits in direct buried cable systems, in non-metallic conduit duct banks, or above groundcable raceways. In such cases, the following shall apply:

a. Main ground return conductors shall be run within the same cable trench or above ground cable racewayas their line conductors.

b. Main ground return conductors shall be run within separate conduits in the duct bank.

c. It is preferred that common ground return conductors be tapped or connected to local ground bars andindividual conductors run to the equipment enclosures along the route of the circuit conductors.

Alternatively, the main ground return conductor may be looped and connected to each equipmentenclosure.

d. Insofar as possible, main ground return conductors and their branch conductors shall be arranged tomaintain minimum spacing to their associated line conductors.

e. If more than one main ground return conductor is used, they may be bonded together and a singleconductor used for connection to equipment enclosures.

f. Main and branch ground return conductors shall be bare stranded medium-hard-drawn copper with aminimum size of 2 Awg (35 mm2).

OVERVOLTAGE PROTECTION FOR POWER SYSTEMS

R 8.1 Power systems with supply circuits or distribution circuits subject to over-voltages from lightning orswitching surges shall be protected against over-voltage by the use of lightning arresters and, if needed,capacitors.

R 8.2 Arrester ground connections on dry type transformers having sheet metal enclosures shall be made bygrounding conductors run in as direct a path as possible to the transformer grounding pad.

R 8.3 The ground terminals of lightning arresters which are installed at the junction of insulated cables andoverhead spacer cables or open wire lines, shall be grounded per the following:

a. Metallic sheaths of multi-conductor cables and multiple-grounded metallic sheaths of single conductorcables shall be connected to the lightning arrester grounding conductor.

b. Single point grounded metallic sheaths of single conductor cables shall be connected to the lightningarrester ground terminals and the arrester shall be grounded through an isolating gap.

c. Metallic conduits shall be connected to the lightning arrester grounding conductor.

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OVERVOLTAGE PROTECTION FOR POWER SYSTEMS (Cont)

d. For situations not covered by subpar. a., b., or c. above, a ground return conductor within non-metallicsheathed multi-conductor cables shall be connected to the lightning arrester grounding conductor, or

e. Alternatively, a ground return conductor within the non-metallic duct carrying non-metallic sheathedcables shall be connected to the lightning arrester grounding conductor.

f. Grounding conductors shall run in as straight and short a path as possible from arrester groundingterminals to the grounding electrode.

g. Conductors on wood poles shall be covered from arrester terminals to below ground by weatherproofjackets, insulation or wood ground moldings.

STRUCTURE LIGHTNING PROTECTION

I 9.1 Any structure within a zone of protection may be considered to be adequately shielded against lightning

so that further protection is not required.

S 9.2 For structures which do not contain appreciable quantities of flammable and combustible material or whichare not part of process or offsite facilities, the zone of protection is:

a. For 50 ft (15 m) heights and lower, the space under a cone with apex at the highest point of a properlygrounded metal structure, mast, wire or air terminal with radius twice the height if the height does not

exceed 25 ft (7.5 m), or radius equal to height if the height does not exceed 50 ft (15 m).b. For heights above 50 ft (15 m), and alternatively for 50 ft (15 m) and lower, the space underneath a

rolling sphere. The space can be determined using the relationship in par. 9.3. Since ANSI/NFPA 780

Chapter 3 uses 150 ft (45 m) striking distance, 300 rather than 200 is used in the relationship.

S 9.3 For structures containing appreciable quantities of flammable and combustible materials or which are part ofprocess or offsite facilities, the zone of protection is:

a. The space underneath a rolling sphere as determined by the relationship:

d = )h200(h)h200(h 2211

d = horizontal distance protectedh1 = height of the properly grounded structure, mast, wire or air terminal, 100 ft maximum

h2 = height of structure or equipment to be protected

Striking distance is 100 ft (30 m) as specified in ANSI/NFPA 780 Chapter 6.

C 9.4 Metallic structures for storage of liquids that can produce flammable vapors or for storage offlammable gases that are electrically continuous, tightly sealed to prevent the escape of liquids, vapors orgases and have thickness not less than 3/16 in. (4.8 mm) sheet steel are inherently self-protecting and needno additional lightning protection. For the purposes of this paragraph, fixed and floating roof atmosphericstorage tanks, and any vessels or pressure storage spheres equipped with pressure relief valvesdischarging to atmosphere shall not be considered tightly sealed and shall meet the requirements ofPar. 9.7.

S 9.5 Important structures not within a zone of protection (i.e., not shielded) or are not inherently self-

protecting shall be protected against damage from lightning. The following structures are consideredimportant.

a. Structures which are normally occupied by personnel.

b. Structures which contain appreciable quantities of flammable and combustible materials.

c. Structures which if seriously damaged could result in a major loss either in the structure itself or from the

effect on other facilities. Most substations are in this category.d. For structures not covered above, risk assessment procedures are provided in regional and national

standards and shall be used to determine if lightning protection is required.
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S 9.6 Important structures which are not within a zone of protection (i.e., shielded) or are not inherentlyself-protective shall be protected as follows:

STRUCTURE LIGHTNING PROTECTION METHOD

a. Metallic Structures:

(including storage tanks, vessels, and buildings withmetallic frames or metallic siding)

Ground as required by Par. 9.7

b. Non-Metallic Structures:

(includes buildings with non-metallic frames and siding)

PerANSI / NFPA 780 or an equivalent nationalstandard

S 9.7 Lightning protection requirements for metallic structures shall be per the following:

STRUCTURE FOUNDATION TYPE GROUNDING REQUIREMENTS

1. Tank bottom resting on non-reinforced concrete pad Ground at perimeter spacing intervals notexceeding 100 ft (30 m) with at least 2locations at opposite extremities

a. Storage Tanks

2. Tank bottom resting on any of the following types of padconstruction: reinforced concrete; ringwall construction;

asphalt, oiled sand, crushed stone pads

None (Adequate grounding)

Note: If tank is resting on an impermeablemembrane, the requirements ofPar. 9.7 a.1 shall be met.

1. Column or skirt supports resting on a reinforced concretefoundation which meets all of the following:

(a) The below grade footing contains at least 20 linearfeet (6 m) of reinforcing bar which is not less than1/2 in. (12 mm) diameter.

(b) The piers or pedestal includes vertical bars orlapped dowels which continue into the footing.

(c) The anchor bolts are embedded in the concrete, andhave metallic contact with the vessel.

None(Adequate grounding)

b. Vessels or PressureStorage Spheres

2. Supports resting on foundations not meeting all of theabove (Item 1)

Ground at perimeter spacing intervals notexceeding 100 ft (30 m) with at least 2locations at opposite extremities

c. Structure, or Building Construction with metallic frames or metallic siding Ground at perimeter spacing intervals notexceeding 100 ft (30 m) with at least 2locations at opposite extremities

S 9.8 Bonding of metallic structures.

a. Floating roof tanks: Bonding between roof and shell shall be provided by the tank vendor for those

designs requiring it (for example: pantagraph type). Provisions shall include the requirements for bothprimary and secondary seals.

b. Buildings: All metallic parts forming the roof and main framework shall be bonded to each other.

c. Metallic bodies of considerable size located inside of metallic structures and which are within 6 ft(2 m) of the structure roof or frame: the metallic body shall be bonded to the structure if not inherentlybonded.

S 9.9 Cables connecting metallic structures to grounding electrodes shall be routed in as straight and direct

path as possible. Spacing of approximately 2 ft (600 mm) shall be maintained, where possible, betweenartificial grounding electrodes and concrete or masonry foundations.

S 9.10 Grounds shall be buried conductors, concrete encased electrodes, artificial grounding electrodes or

combinations. Resistance to earth shall not exceed 15 ohms.

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INTERNATIONAL

PRACTICE

SECONDARY EFFECTS OF LIGHTNING

R,I 9.11 The basic lightning protection system provides the required low impedance metal path required tointercept, conduct and dissipate the main lightning discharge of strikes on the protected structure. It doesnot assure safety for all equipment and circuits, particularly electronic systems using solid state components,

from the possible secondary effects of lightning strikes on the structure, the adjacent area, or oninterconnected structures.

Additional provisions may be required to protect against inductive and resistive overvoltages which

may be produced on circuits and at equipment by the main discharge current or by currents entering onutility services, and on control, communication and data transmission circuits. Regional and nationalstandards contain information covering assessment and recommendations for coping with the secondary

effects.

BONDING AT TANK TRUCK, TANK CAR, OR CONTAINER LOADING STATIONS

S 10.1 Bonding is required only when all of the following loading conditions exist:

a. Loading is through open domes or into open drums, caps, cylinders or similar metallic containers.

b. The product loaded: (1) has a closed cup flash point below 100F (37.8C); (2) is handled within 15F

(8C) of or above its flash point, or (3) is switch loaded into a tank truck or tank car previously carrying

material with a closed cup flash point below 100F (37.8C).

c. The product is classified as a static electrical charge accumulator.

C 10.2 Bonding is not required around flexible metallic joints or swivel joints or when loading conditions are as

follows:

a. If tank car or tank truck loading is through a closed system.

b. If container filling is through a closed system, or if the filling nozzle is in electrical contact with thecontainer and will remain so throughout the filling operation.

S 10.3 Tank truck bonding conductors, when required, shall be provided at each loading or unloading position

as follows:

a. One end of the conductor shall be permanently connected directly to the fill stem, or to other points onthe piping or steel loading rack which are electrically connected to the fill stem (either inherently orthrough bonding connections).

b. A battery type clip (or equivalent) shall be connected to the other end of the bonding conductor.

Conductor shall be long enough to permit attachment of the clip to the truck at a point that is in metalliccontact with the cargo tank being loaded or unloaded.

c. Bonding conductor shall be a 6-Awg (16 mm2) single conductor rope-stranded copper cable. Cable shallhave a thermosetting jacket for mechanical protection of the conductor.

S 10.4 Tank car bonding, when required, shall be as follows:

a. Insulating rail joints shall be provided to isolate from the main track the track section upon which cars willstand while being loaded or unloaded. Their joints are to isolate stray currents resulting from signal orpower systems on the main track.

b. Joints shall be located to avoid being bridged by standing cars not loading or unloading.

c. Bond around all rail joints in the track section upon which cars will stand while being loaded or unloaded.

d. Bond both rails of the track section upon which cars will stand while being loaded or unloaded to theloading rack steel structure. If not inherently bonded together, the loading and unloading piping shall bebonded to the loading rack steel structure.

S 10.5 Container bonding, when required, shall keep the filling nozzle and container at the same electricalpotential to prevent a possible static spark in the area of a flammable mixture. Bonding shall be as follows:

a. When the filling nozzle may not be or remain in electrical contact with the container, the container shallrest on a metal base plate while being filled. This base plate shall be bonded to the supply piping.

b. If the filling nozzle is inherently bonded to the supply piping, such as by the use of metallic hose or pipe,no additional bonding to that specified in (a) is required.

c. If the filling nozzle is not inherently bonded to the supply piping, such as when a nonmetallic hose orpipe is used, an additional bond shall be provided between the nozzle and supply piping.

d. All metallic parts of the fill assembly shall form a continuous electrically conductive path downstreamfrom the point of bonding on the supply piping.

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THIS INFORMATION FOR AUTHORIZED COMPANY USE ONLYEXXON RESEARCH AND ENGINEERING COMPANY FLORHAM PARK N J


PROTECTION AT MARINE TERMINAL LOADING STATIONS

C 11.1 Bonding is not required between tankers or barges and the marine pier.

S 11.2 Electrically insulated flanges are required to electrically isolate on-board (tanker or barge) piping from thepier piping:

a. At cathodically protected marine terminals.b. Where marine loading arms or electrically bonded oil cargo hoses are used.

c. For loading and unloading products having a closed cup flash points below 100F (37.8C), or which are

at a temperature above or within 15F (8C) of their flash point.

Revision Memo

9/68 Original Issue of Basic Practice 1/79 Revision 2

1/73 Revision 1 6/81 Revision 3

12/94 Revision 0 - Original Issue of International Practice

3/98 Revision 1

6/00 Revision 2Par. 1.2 alerts Contractor to instrumentation needs in the earthing system. Pars. 2.1 and 2.2 reference made to additionalstandards. Par. 3.6 early streamer lightning protection was deleted and lightning arrester was added. Par. 4.11 added IEEE Std837 type connectons. Par. 4.15 deleted extraneous wording. New Par. 4.16 specifies areas requiring special grounding systemdesign and OE approval. Par. 9.4 added clarification regarding storage tanks and vessels with pressure relief. Par. 9.7a.2 nowrequires grounding at all storage tanks with impermeable membrane. Par. 11.2 purpose code changed from R to S.

Exxon Research and Engineering Company, 1998, 2000
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160401

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