22674566 distribution system grounding fundamentals

7/29/2019 22674566 Distribution System Grounding Fundamentals

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Conference Papers

0-7803-8298-6/04/$20.00 020041EEE

Distr ibut ion System Grounding Fundamentals

Edward S.Thom as, PE, Uti t l ty Electr ical Consultants, PCRichard A Barber, Uti t l ty Electr ical Consu ltants, PCJohn B. Dagenhart, PE, Clapp research A ssoc iatesAl len L. Clapp, PD PL S, Clapp research A ssoc iates

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Distribution System Grounding FundamentalsEdward S. Thomas, PE - Senior MemberRichard A. Barber - MemberUtility Electrical Consultants, PCRaleigh, NC 27601

- The most common medium voltage electricdistribution system in the United States is multigroundedwye using a common neutral for both primary andsecondary systems. The effective interconnection of themultigrounded wye neutral conductor with the earth groundreference is very im portant for safe and effective operationof these systems. Areas of concern include:Public SafetyOperating Personnel SafetySystem R eliabilityPowerQuality

0 . Customer Surge ProtectionThis paper-is intended to address how grounding systemeffectiveness affects each of these goals.Kev Words - Grounding. Earthing, Safety, SurgeProtection. NESC, Neutral-to-Earth Voltage, GroundCurrents, Stray Voltage.

1 INTRODUCTIONThis paper is intended to give an overview of the

various relationships between neutral currents, groundcurrents, electrode impedances and voltage potentials thatare encountered in the grounding of multigrounded wyedistribution systems. This system configuration is the mostcommonly used configuration among U.S. domesticutilities. Vo ltages range from 4.16/2.4 kV to 3 4 3 1 9 .9 kV.The most common system voltages are 15 kV and 25 kVclass systems with nominal operating voltages on ruralsystems generally being 12.47fl.2 kV and 24.9/14.4 kV .The paper is intended to review the relationships whichmight & encountered due to system grounding and providean overview of common installations and their relativeeffectiveness.The NESC requires multigrounded distribution systemneutrals to be effectively grounded (Rule 96C). Thedefinition of effectively grounded is as follows:

Effectively Grounded. Intentionally connected toearth through a ground connection or connections ofsufficiently low impedance and having sufficientcurrent-carrying capacity to limit the buildup of

John B. Dagenh art, PE - Senior MemberAllen L. Clapp, PE, PLS - Senior MemberClapp Research AssociatesRaleigh, NC 27612voltages to levels below that which may result inundue hazard to persons or to connected equipment.Effective grounding, or earthing, of the distributionsystem neutral is necessary to achieve several .objectives,the most impo rtant of which is the safety of the public andutility personnel. The effectiveness of the grounding systemalso affects system reliability, power quality, and thelongevity of both utility and customer equipm ent. Effective

grounding and bonding reduces voltages between adjacentgrounded facilities within utility and publidcustomerinstallations.For all of these objectives, the general method toachieve maximum effectiveness of the utility groundingsystem is to establish the best practical connection betweenthe neutral conductor and the earth. Decreasing theresistance in this connection reduces bo th

the effect of lightning discharges on or near utilityor customer facilities, andthe effect of neutral-to-earth (NTE) voltages thatmay exist between the neutral and earth.0

A low neutral-to-earth impedance is particularlyimportant when the distribution system neutral is connectedto metallic objects that are accessible to the public. Theseobjects include guy wires, pole grounds and the customer-owned wiring and plumbing within a residence or otherbuilding. If these classes of metallic objects are notinterconnected to the distribution system neutral, therecould be a strong local voltage difference between theseobjects, either on the utility facilities or within customerpremises. Bonding of grounded conductors of circuitsentering customer facilities is required to assure the safetyand reliability of customer equipment.The importance of effective grounding and bonding isrecognized by both the National Electrical Safety Code(NESC) (ANSI C2) and the National Electrical Code(NFPA 70). Both codes require interconnection of thepower, telephone, CATV, and customr groundingconductors at the served installation, in order to limitvoltage potentials that may be hazardous to personnel orequipment.

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Another area w here interconnection of system neutralsis important is with the other utilities, principallycommunication utilities, that occupy joint use structures andenter the same customer premises as the electric systemneutral. In order for joint-use o ccupants to minimize utilitystructure size, adjacent grounded facilities must be bonded.Otherwise, workers could be exposed to steady state andlortransient voltages between metallic objects within closeproximity to each other. Of course, when bondinginterconnects the electric utility distribution system neutralwith messengers or cable shields of com munication utilities,any NTE voltages on the dishibution system neutral areimposed on the communication utilities. This results incommunications utility messengers and cable shieldssharing the flow of neutral currents. Consequently, it isimportant for the electric utility to be effectively groundedto m inimize the existence of these currents.

11. NEUTRAL-TO-EARTH IMPEDANCEThe effective impedance of a neutral-to-earthconnection is significantly affected by the area and shape ofthe electrode, the depth of the electrode, and the resistivityof the earth surrounding the electrode.As the surface area of the electrode increases, currentdensity across the surface decreases. Since electrical lossesin the form of heating are a function of the square of thecurren t flow (I"), a larger surface area (a) produ ces lessheating (drying) of the earth around the electrode for thesame ov erall current flowing across the electrode and, thus,(b) allows more current to flow through the eanhsurrounding the electrode for a longer period of time. Just asan incandescent bulb ( a high-intensity point source of light)

is more difficult to view with the eye than a fluorescent bulbwith the same total light output (a low-intensity, linear lightsource with more surface area), a linear ground electrode,such as a rod or strip, is often more effective than a plate orcoiled electrode, because the former have access to moreearth w ith which to dissipate the energy.As soil depth increases, so generally does bathmoisture and pressure, both of which increase soilconductivity and reduce resistance of the electroddsoilinterface.The resistivity of the soil significantly affects theability of an electrode to transfer current to the earth fromutility system electrodes. A value of 100 0 - m (ohm-meters)

is commonly used to represent typical earth resistivityaround utility ground electrodes. An earth resistivity of 30a-m (3000 a-cm) or less is considered by the NESC to below resistivity (NESC C ommittee comm ents in 15 August1973 Draft of NESC Part 2 1977 Edition). However, theresistivity of dry sands and gravels can be 1000-3000a - mor even higher. T herefore, the resistance of electrode insuch soil can be more than an order of magnitude (IO imes)

higher than shown by a typical calculation assuming 100 a -m. The value of soil resistivity must be known with areasonable degree of certainty before any meaningfulcalculations can be made.

111. TYPES OF GROUNDING ELECTRODESThe electric utility distribution system, due to itsversatility and interconnection with o ther utilities, offers awide variety of grounding electrode categories. It isimportant to understand the propenies and function of eachtype of grounding electrode.

A. Substation Groun dsThe ground ma t at the substation serving as a sourcefor the distribution circuit is one of the paths for neutralcurrent to return to the transformer neutral connection.While distribution system neutral grounds near thesubstation may also pick up some of the earth reNm cu rrent,the substation ground mat is generally the principal route forearth currents. This is due to the relatively low resistance ofthis element when compared with the resistance of otherground connections in the vicinity of the substation. Theresistance of substation ground mat should always be lessthan 10 ohms. Typical ground system im pedances for smallsubstations with lower fault currents generally fall between2 and 7 ohms. With good design, mats which cover largeareas may achieve impedances of less than one ohm. Thehigher the available fault current or the net neutral current inthe station, the greater will be the need fo r an effective, low-impedance ground system. See E E E Standard 80-2000 formethods to limit touch, step and mesh potentials.

B. Distribution System Neutral Ground sNESC Rules 96C and 97C require that a neutral onmultigrounded wye distribution systems have a minimum offour ground connections in each mile. The four-grounds-per-mile rule also applies to URD cables with insulatingjackets. Treatment of these underground cable groundingelectrodes should be the same as with the distributionsystem neutral grounds.Distribution system neutral grounds are generally thesame configuration as equipment grounds and typicallyhave the same resistance characteristics.

C. Equipm ent Ground ing ElectrodesEquipment grounding electrodes are normally drivenground rods. The requirements for equipment groundingelectrodes are found in NESC Rule 94. These are installedfor each distribution transformer or lightning arresterinstallation. The NESC requires a minimum electrodenominal diameter of 1/2" or 5/8" , depending upon material,and a minim um buried length of 8'.This resistance achievedwith a 518" diameter 8 ft long rod is approximately 40 in

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100 n- m s oi l or approximately 12 n n 30 n - m soil. Actualinstalled resistance will vary widely depending upon soilresistivity. These ground rod electrodes may be used tomeet bath the transformer grounding requirements and thefour-grounds-per-mile requirement of NESC Rules 9 K and9 7 c .D. Pole Grounds

On some systems, it is common to install a poleground at each pole to (a) protect the pole from lightninguntil the conduc tors are installed and (b)help decrease NTEimpedance after the neutral is installed. These pole groundsgenerally consist of a grounding conductor installed fromthe neutral of the distrihution system down the pole to thebun. In some cases the pole ground w ill extend to the top ofthe pole. The butt end of the pole ground is commonlyterminated in a bun w rap on the last two feet of the pole or abutt coil on the base of the pole. In some .cases the poleground is attached to a butt plate (in lieu of a butt coil)which provides a plate electrode approximately the diameterof the pole butt.The 60 Hz esisiance of po le ground s is generally high. Thisis due to the s m a l l diameter of the conductor, the shadingeffect of the non-conductive pole and the relatively poorcontact of the conductor with the surrounding soil (i.e.,backfdl). On some types of poles, the leaching of thepreservative may form a high resistance film between thegrounding conductor and the surrounding earth. The polebutt plates, if they do not develop an insulating film. ma yhave a 60 Hz resistance of approximately 150 ohms in 10 0oh-meter soil. These butt-wrap and butt-platelcoil poleground electrodes are not as effective as a driven ground rodand may not he used as the sole electrode at atransformerlarrester location (NESC Rule 94B4a).However, if installed in an area with low so il resistivity (30n - m or less), one such electrode may be considered as halfof an electrode for purposes of meeting the four-grounds-per-mile requirements of NESC Rules 96C and 97C.E. Customer Grounds

National Electrical Code (A 70) Article 250.52requires that all custom ers receiving electric service attach agrounding conductor fm m the service entrance equipment toan existing electrode or a made electrode installed for thepurpose. The minimum dimensions for ground rodelectrodes are 518" x 8'. If a single electrode does not have aresistance of less than 25 ohms, the installation of a secondelectrode is required. Experience indicates that the averageelectrode resistance achieved by the custom er is greater than25 ohm s, unless soil resistivity is sign ificantly less than 100n- m ( i. e. , 60 n-m) or a multiple-electrode groundingelectrode system is used. Another factor causing highcustomer ground resistance is the practice of driving rods

immediately adjacent to building foundations where soilmoisture content (and thus conductivity) may be lower.F. URD Cable wth Bare Concentric Neutral andCounterpoise Conductors in Direct Contact wthEarth

For purpo ses of grounding calcu lations, the concentricneutral on older underground residential distribution cableswith hare neutral wires in direct contact with earth (not inconduit) can be treated as an equivalent counterpoiseconductor. NESC Rule 94B5 allows 100 A of bareconcentric neutral cable (or cable with a semiconductingjacket of I0 0 n -m or less radial resistivity) to be consideredas equivalent to a ground rod. When placed in soil of 100n - m resistivity, the neutral-to-earth impedance isapproximately 6 n.The 60Hz mpedance of a counterpoisecan he calculated using Reference B7 (Equations 5.13 and5.14) and Reference C4 (pages 307-312). A reasonableestimate for a 250-fmt length of 15 kV unjacketed cablewith a full concentric neutral would be between 2.0 ohmsand 2.6 ohms at 60 Hz in 100 ohmmeter soil. Atunderground riser poles this resistance can be considered asbeing connected in parallel with the ground rod normallyinstalled at that location. When depending on a counterpoiseas the principal electrode at a loc ation, careful considerationshould be given to seasonal variations in soil resistivity atthe counterpoise burial depth.G. Metallic Water Distribution Systems

Article 250.104 of the National Electrical Coderequires that all customer neutrals be interconnected(bonded) with metallic water piping within the customer spremises. The purpose of this requirement is to eliminateany voltage differential between these systems and, thereby,minimize the opportunity for shock to customers in contactwith both water piping and an electrical applianceconnected to the distribution system neutral. By virtue ofthis bonding, any neu tral voltage existing on the distrihutionsystem can impose a current onto the customer service. Thiscurrent is distributed to earth through the customer pipingandor any interconnected municipal water supply piping.Of course, the use of plastic pipe in the customer s waterservice or in the community water distribution systemslimits the flow of earth r e m current to thoseinterconnected metallic piping sections which aTe in contactwith earth.If the customer has a 100 foot section of 314 copper linebetween the water meter and house, resistance of this linesection will be approximately 5.8 ohms and will be in aparallel path with other distribution system neutral earthconnections. If the copper service line is connected into1000 feet of 6 inch bare metallic water distribution main,the resistance to earth of that pipe section would beapproximately 0.6 ohms in 100 n - m earth. It is apparent

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- -DlSTRiBUnON SYSTEM PHASE CONDUCTOR LI tL 2 L11cSOURCETRANSFORMERAT SUBSTATION

EARTH UG - UTILITY GROUNDCG - CUSTOMER GROUND'--. UGItUGZtUG3tUG4-UG5tCG1 CGZflCURE 1 - SIMPLIFIED MULnGROUNDED WE DlSTRlBUnONSYSTEM PRIMARY NEUTRAL CIRCUIT

that some sections of community water distribution systemscan be very effective ground paths for neu tral return current,even if the piping is not continuous hack to the distributionsubstation which is the source of the distribution circuit. Bybeing connected in parallel with the customer distributionservice entrance ground, any existing water system groundswill greatly reduce the effective ground electrode resistanceof the average customer service.IV. NEUTRAL-TO-EARTH VOLTAGE SOURCES

The voltage between a neutral and nearby earth canoriginate with a variety of sources and can take at least twodistinct f o m . The area of most common concern from apublic safety standpoint is the 60 Hz voltage that may existbetween objects connected to the neutral and earth. This isparticularly important as the distance increases between thebonded object and an effective grounding electrode. Boththe magnitude and duration of the "E voltage areimportant factors.

A second type of voltage that will appear betweenneutral and earth is the extremely short duration transientoccurring when lightning is dissipated into the earth, eitherthrough a direct strike to the utility neutral or when surgeprotection equipment passes the lightning stroke chargefrom energized conductors to the neutral and itsinterconnected grounding electrodes. This typically occursas a high frequency, steep wavefront event, such as a 95x 50microsecond or longer waveform.

A. Steady-State60Hz VoltageFigure 1 shows a simplified multigrounded wye distributionsystem with multiple ground connections on the primaryneutral and multiple customer loads. Magnitudes anddirections of current flow shown in Figure I are simplifiedfor discussion purposes and may vary greatly depending onlocal conditions. The following discussions will furthersimplify this circuit in order to show the effect of differentconditions.The predom inant source of NTE voltage is the steady-statecondition that is created by voltage drop in the systemneutral conductor as current passes through this conductor.To use an extreme case as an example, consider a long,single-phase line where the neutral conductor ha s nogrounding. See Figure 2, Scenario 1. All of the load currentmust pass through the neutral conductor. This will generatein the neutral conductor a voltage drop equal to that in aphase conductor of the same size and composition. As anexample, if a two-mile long 110 ACSR single-phase linecarries I mpere to a load at the end of the line and theneurral is effectively grounded at its source, the voltagedrop in each conductor of this line would be approximately1.37 volts. Given the condition of the effective grounding atthe source of the tap, the voltage between the neutralconductor and earth at the load point would be 1.37 volts.

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I4 FAULT

1AMP LOAD 1 AMP LOADNO GROUND I Q GROUND

AT LOAD AT LOAD

FIGURE 2 - HYPOTHETICAL CIRCUITFOR EXAMPLE CASE

FAULT FAULTNO GROUND I Q GROUND

AT LOAD AT LOAD

DATA FOR FIGURE 2 CIRCUIT

AB

OHMS~ =a 1 - 1AMPS1 0 0.41 0 I 1341I 1 I I I I I I

I I I I I I I I I IPOINTI UNIT I ISCENARIOI ISCENARIO1 ISCE NARIO 31 ISCENARIO1I I I I I I I I I I I

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o IVOLTSIIn order to improve this situation, a single ground with aneffective impedance of I C l can he hypothetically added atthe load point. See Figure 2, Scenario 2. This creates aparallel path for the flow of current back from point A to thesystem source. In this extremely simplified case, the NTEvoltage at point A would he reduced IO 0.41 volts. Whilethis is a simplified version of conditions on an elecmcaldistribution system, the example does illustrate theprinciples involved in reduced NTE voltage throughgrounding.Current in the distribution system neutral is not solelycaused by customer load on single-phase taps. It can alsocome from unbalanced load on multigrounded wye three-phase lines. The neutral current is created when the single-phase loads connected to each phase are unequal and aresultant neutral current is created. Good distributiongrounding will reduce the NTE voltage along the neutralpath.

A special case .of unbalanced single-phase loadcreating neutral current is the application of single-phasecapacitors. Each 50 kVAC unit creates a capacitive currentof seven amperes on a 1.2 kV system. If this is not locallycompensated by an equal reactive current, it adds to thesystem neutral current and, thereby increasesNTE voltage.

1.37 I 0.41 I 3600 1 1341Again, effective neutral grounding will reduce the resultingNTE voltage.B. Electrical Faults onCustomerWiring

A second source of steady-state NTE voltage isimproper wiring on customer premises. For example, if anenergized conductor contacts an unbonded well casing, theresistance of the circuit between the well casing and thesecondary neutral may be high enough IO limit the currentflow below a value that would result in tripping of the low-voltage breaker. As illustrated in Figure 3, if the well casing(in this case unbonded) has a resistance to remote earth of 6ohms and the distribution system neutral has an effectiveresistance of 4 ohms, the fault current is 12 amperes, whichis insufficient to operate the circuit breaker. The f l ow of 12amperes through the neutral-to-earth resistance of 4 ohms atPoint A will create a potential of 48 volts between theneutral and earth. The fault current through the resistance atPoint B will create a voltage between the well casing andremote earth of 1 2 volts. The relative voltage at each pointwill be inversely related to the impedance of each earthconnection. If the well casing is bonded to the premisesgrounding system as required by NEC-2002 Article250.1IZ(M), the breaker operates and these potentiallyhazardous voltages do not occur. However. this bond issometimes missing.

120"240"

.....~~

E W l P M E N lEFFECTWE NTE 0 FAULT CURRENTRESISTANCE = 4 0

N E RESISTANCE-----.___WELL12 A GROUND CASING

FAULT CURRENT

CONTACT

"CURE 3 - CUSTMIER *IRINGFAULT EXAMPLE

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C. Faults on Utility Pr ima ry SystemThe most common type of short circuit on the

multigrounded wye distribution system is the phase-to-ground fault. This can occur either on three-phase feeders oron single-phase tap lines. Regardless of location, the effectupon neutral-to-earth voltage is essentially the same. Thiscondition is principally differentiated from the steady state60 Hz condition by the ma gnitude of the currents which areflowing in the distribution system neutral. The magnitude ofthe fault current which flows through phase conductors ispartially determined by the impedance of theneutrallgrounding system network. Lower neutral-to-earthresistance will reduce the effective impedance of theneutrallearth network and thereby generally result in aslightly higher current for a given fault situation. This canfacilitate practical overcurren t coordination solutions.

The analysis illustrated in Figure 2, Scenario 3, showsa 7.2 kV sing le-phase line with an ung rounded neutral and abolted phase-to-neutral fault ahead of the transformerprimary winding. The voltage drop along the neutral is thesame as the voltage drop along the phase conductor. Thismeans that the 7200 volts of source potential is dividedequally between ph ase wire and the neutral. This results in a3600 volt neutral-to-earth potential at the fault location andat all points beyond. The consequent safety hazards of thishypothetical situation without a transformer groundelectrode are obvious.

In Figure 2. Scenario 4, a more realistic scenario ispresented, similar to Figure 2 . Scenario 2. It can he seen thateven with a I Cl neutral-to-earth impedance at the point ofthe fault the NTE neutral-to-earth potential is approximately1341 volts. Obviously, appropriate bonding and additionalgrounding of the distribution system neutral is needed toensure safety.

Another aspect of phase-to-ground faults on amultigrounded wye primary system is the electrical shift ofthe neutral due to flow of fault current in the neutral path.This manifests itself in elevated voltage between the neutraland remote earth with consequent current flows from theneutral to earth. It also results in a temporary elevatedvoltage between the neutral and t he un faulted phases. For aneffectively grounded system this will result in a transientphase-to-ground voltage of less than 2.0 pu. This is to beexpected when XdX l


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and directly to the system neutral which serves as agrounding conductor for the equipment tank. The arresterhas accomplished its function of reducing the voltage acrossthe equipment insulation system. By virtue of its closeconnection between the primary conductor and theequipment tank. the optimum equipment protection hasbeen achieved regardless of whether there is an effectiveearth ground at this location. However, in 'this case thelightning charge has been shunted from the primaryconductor to the neutral conductor. If there is not aneffective ground electrode at this point, the lightning surgewill then propagate along the system n eutral until it can betransferred to eanh through grounding. During the surge.the rise in the neutral voltage relative to remote earth is afunction of the distance to effective grounding electrodesand the surge impedance of the path(s). As explained below,even the presence of a ground electrode at the arresterlocation will result in a surge voltage being present on theneutral. The magnitude of this voltage is a function of surgemagnitude, wave shape, downlead length and groundingelectrode surge impedance. The importance of the surgevoltage on the neutral lies in the effect which this can haveon customer premises which are interconnected with thesystem neutral. One of the paths along which the surgecurrent is dissipated in the secondary neutral. See Figure 4.This means that part of the current travels through thecustomer s service entrance grounding electrode. Since theservice entrance ground generally has a higher impedancethan the utility equipment ground, a lesser portion of thetotal discharge current travels along this neutral path and initself is not detrimental to customer premises which havegood bonding in place. However, with secondary servicecables in a triplex configuration, a surge current travelingthrough the triplex cable neutral will induce a voltagebetween the neutral and the energized conductorssurrounding the neutral. [F2,F71 he surge voltage inducedin the energized conductors is proportional to the surgecurrent in the secondary neutral which is a function of therelative impedances to eanh of the distribution systemneutral and the customer prem ises grounding system. If thesystem neutral ground impedance is high in relation to thecustomer ground, more of the current will travel along theservice neutral and the induced voltage will he higher. Thisinduced voltage will be present at both ends of the service.Thus it is apparent that a high impedance earth ground at autility equipment location can have an adverse effect onboth the customer and the utility transformer secondarywindings, even when protection of the transformer primarywinding ha s been effectively accomplished. Therefore, oneimportant component of total system surge protection is aneffective equipment ground electrode at transformers.B. Line P rotection

Another function of the distribution arrester is theprevention of flashovers between the primary conductorsand the structure (or other phase conductors) during direct

or nearby strokes. Here the lightning surge current must hetransferred from the primary conductors to earth aseffectively as possible in order to minimize the voltageexisting across the stmcture insulation system. Thisminimizes the probability of a phase-to-ground flashoverwhich will cause facility damage andor line interruption.The voltage from the primary conductor to ean h during anarrester discharge depends to a significant extent on theresistance to earth of the grounding electrode at the arresterlocation. See Figure 4. The local grounding electroderesistance will partially determine the surge voltage betweenthe protected conductor and other parts of the structure ifonly one phase is protected. However, for the more commoncase where all energized conductors have surge protection,only the arrester characteristics and the length of the arresterleads determine the degree of protection against flashoverbetween conductors. Since the objective is to preventflashover on the structure or between the energizedconductors, the equalization of voltages at the pole top issometimes adequate to accomplish the desired result.However, the presence of a low impedance groundingelectrode at the arrester location will enhance chargedissipation from both the neutral and the energizedconductors. This will reduce the magnitude of the wavepropagated along both the energized conductors and alongthe system neutral. Therefore, it is apparent that whilestructure flashover performance might be improved withoutan effective grounding electrode at the arrester location,total performance of a practical distribution system stillrequires a low impedance arrester ground.C. Underground Protection

The local grounding of underground cable dips is aspecial case of surge protection. Underground equipmentsusceptibility to lightning surges and the wavefrontdoubling phenomenon on underground cables makesreduction of wavefront magnitude very important. Th esurge voltage imposed on the primary cable system andattached equipment is most effectively reduced by closeconnection of the lightning arrester to the cableterminations. This is accomplished by minimizing theeffective lead length. The effectiveness of cable andequipment protection is not strongly dependant on riser poleground electrode resistance. However, the arrester dischargeat a properly installed pole-top termination also impo ses asu rg e c a n t a nd v olta ge )onthe pole ground and the cableconcentric neutral or shield.In bare concenhic neutral (BCN) cables the cableneutral surge current is then dispersed to eanh in theimmediate vicinity of the pole. For jacketed concentricneutral (JCN) cables there will exist a voltage across thejacket which will be proportional to the share of arresterdischarge current passed along the cable n eutral. Therefore.to minimize the probability of jacket punctures, andattendant corrosion potential for the neutral, the resistance

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of the riser pole grounding electrode should be kept as lowas practical. A target resistance of 10 0 s considereddesirable.The amount of current distributed into the riser poleground electrode. the system neutral and the cable neutral isdependant on the relative impedances of each. When thecurrent surge passed along the JCN cable neutral reaches thefirst transformer, there is a partial dispersion of this neutralsurge current among the transformer grounding electrode,other JC N primary neutrals and the secondary serviceneutrals originating at the transformer. Therefore, part of theriser pole arrester discharge current can be eventuallytransferred to the customer s service entrance groundelectrode with the secondary surge induction problemsdescribed elsewhere in this paper. This is additionaljustification for keeping grounding electrode resistance lowat both the riser pole and the padmount transformer.

D. Grounding System Surge ImpedanceConsideration of grounding system surge dissipationeffectiveness must recognize two very imponant differencesbetween surge dissipation and 60 Hz system grounding.First is the extremely steep wavefront associated withlightning strokes and lightning arrester discharge currents.Lightning currents have a wavefront dUdt on the order of 4to 15 kA per microsecond ( W s ) , whereas a 60 Hzwaveform on 7.2 kV system ha s a rise time on the order of

0.0012 kV/:s. This means that the inductance of anyconductor, regardless of size, becomes very large comparedto the resistance of that conductor. The surge voltage indownlead conductors may be in the range of 1.6-10 kVlfoot.Therefore, grounding electrodes separated from the strokelocation can contribute very little to lowering the systemimpedance seen by the surge current. This means that thedissipation of surge current depends upon the effectivenessof grounding electrodes in the immediate vicinity of thelocation where the surge current is imposed upon the systemby a lightning arrester or a system flashover.

The second important aspect of grounding systemsurge impedance is the behavior of grounding electrodesunder high current discharges. Since the impedance of theelectrode to remote eanh occurs as the resistance ofconcentric shells of earth surrounding the electrode, thepassage of the high momentary current associated with anarrester discharge will produce a high impulse voltagegradient in the im mediate vicinity of the ground electrode.This high voltage gradient, occurring within the soil. willresult in arcing through the soil interstices. The presence ofthese microarcs bridge the higher resistance components ofthe soil structure and thus m omentarily lower the electroderesistance to remote eanh during the discharge event. Ofcourse, the magnitude of this effect is strongly dependent onsoil particle resistance, soil moisture resistivity and the soilvoid ratio. Sandy open-grain soils will generally exhibit a

greater percent reduction in electrode impedence than tight-grained clays. [EIS, E191. This is illustrated in Figure 6. Itcan be seen that for im pulse currents of 5000 amperes theimpedance of electrodes in sandy soils may be reduced tothe range of 40.50% of their M) Hz values. Under similarconditions electrodes in clays are reduced to 60.80% oftheir 60 Hz values. However, those grounds which have thelowest 60 Hz impedance always achieve the lowest surgeimpedance.

VI. BONDING B ETWEEN PRIMARY SYSTEMNEUTRAL, TELEPHONE, CATV, AND WATERSYSTEM STypically, electric distribution line primaryneutrals are bonded to telephone and CAT V strands on jointuse lines. This creates an eq uipotential condition betweenthe individual messenger strands and the neutral. Thisreduces the likelihood of hazardous voltages between non-current carrying parts on poles and, by extension, onunderground systems.Communication utilities often do not realize thattheir suppon strands frequently function as part of theneutral return path for the electric utility system. Because ofthis, comm unication workers should exercise caution whenconnecting and disconnecting grounding and bondingconnections on their suppon strand. If the im pedance of theelectric system neutral has increased for some reason, suchas a high-resistance splice, the comm unication strand maycarry a significant ponion of neutral current. The currentsharing is a function of the relative impedances of theelectric system neutral and the respective communication

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messengers and/or shields. Coaxial cables such as found incable television systems provide a particularly lowimpedance path. The current and associated potentials maybecome a personnel hazard if communication personnel d onot follow appro priate work rules.

A very positive aspect of bonding between thedistribution system neutral and the communication system isthe effect which this has on the effectiveness ofcommunication cable sheaths. The sheath efficiency inpreventing magnetic induction in communicationconductors is strongly dependent on the presence of a lowimpedance connection to earth at each end of an exposedcable section. Bonding of the sheath to an effectivelygrounded distribution system neutral provides these groundconnections for the sheath.Although metallic water lines have been used in

the past as grounding electrodes, eleclric utilities typicallydo not bond to these systems except at the served structure.See Section VII.VII. CO DE REQUIREM ENTS

A. .NESC [ A l l - Utility Ground ing and BondingThe requirement to ground utility systems is containedin NESC Rule 215 for overhead systems and Rule 314 forunderground systems. For purposes of discussion and toavoid duplication, the overhead rules will be referenced.although similar underground rules also exist.NESC Rule 97G requires grounded items on joint-use

poles to be bonded by either using a single groundingconductor or bonding the supply grounding con ductor to thecommunication grounding conductor, except whereseparation is required by Rule 97A. Where separation ismaintained according to Rule 97A, insulation may berequired on the grounding conductofls), since there may bea hazardous potential voltage difference between the twoconductors. NESC Rule 215C3 requires bonding betweenmessengers at typically four times in each mile, which isconsistent with the requirement to ground supply neutralsnot less than four times in each mile.Electric and communication systems are requiredby both the NESC and NEC to utilize the same groundingsystem at a structure receiving electric and communication

service. Although NESC Rule 099 allows and specifiesgrounding electrodes for communication systems, when thetwo utilities provide service to a com mon building structure,they are required to create a comm on grounding electrodesystem for the served structure If the two (or more) utilitiesdecide, for whatever reason, to install their own groundingelectrodes (as with different service entrance locations),NESC Rule 099C requires the separate electrode systems tobe bonded with a conductor not smaller than AWG No. 6

copper. National Electrical Code Article 800-40(d) hascorresponding requirements for systems subject to thatCode.If the electric system service and commun icationsystem service do not utilize the same grounding system, asrequired by the NESC or NEC, the different systems maycreate a potential for equipment damage due to voltagesurges. For example, the charging base for the cordlesstelephone set utilizes the electric system for powering thecharging system. As a result, if the grounding systems areno t bonded, there could be two separate grounding systemswithin the body of the charging base. A voltage surge froma lightning impulse (or any other source) imposed on on egrounding system may jump the gap between the twosystems in an attempt to equalize the potential, damagingthe equipment. The same can be said for a cable-readytelevision, VCR, computer modem, or other piece of

communication equipment. Many satellite receiving unitshave a telephone connection for communicating with thesatellite company. This presents a similar problem if thesystems are not properly bonded.B. NEC [A21 - User Grounding and Bonding

Similar requirements for grounding and bondingare contained in the National Electrical Code (NEC).How ever, the system neutral of the utilization wiring systemof a building or structure is not utilized for grounding as isthe neutral o f the electric distribution mulitgrounded neutralsystem. In utilization wiring systems, the voltage drop onthe neutral. if also used for equipment grounding, couldresult in voltage differences between the exposed metallicframes and cases of electrical equipment and appliances.This could produce a hazard to personnel or even a fuehazard.

Nu3 Article 250.24(A)(5) prohibits the bonding ofthe neutral and equipment grounding conductor beyond theservice disconnect. It should he noted that NEC Article250.104 requires electrical bonding to metal water pipesinstalled in or attached to a building or structure. Thislimits the opportunity for a voltage potential difference toexist between the water system and other non-currentcarrying parts within the building. Howe ver, it should alsohe noted that NEC Article 250.52(A)(l) prohibits usinginterior metal water piping located more than 5 feet fromthe entrance to the building from being used to interconnectgrounding electrodes within a building. Note that anyreplacement of metallic water pipes utilizing nonmetallicwater pipes would interrupt the electrical continuity beingprovided by the metallic water pipes.

VIII. CONCLUSIONSThe optimum performance of the multigroundedneutral distribution system is dependent on a good

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connection between the neutral and earth. Advantages ofadequate neutral grounding include the following:Improved public and utility personnel safety byreducing steady state neural-to-earth voltages.* Reduced transient neutral-to-earth voltagesoccurring during phase-to-ground faults.Contributes to reduced surge voltage on customersystems during lightning arrester operations.. Improved cable and equipment protection onunderground systems.Reduced current flow into bonded systems ordevelopment of elevated neutral-to-earth voltagesin case of a broken neutral.These points show the need for continued attentionto good system grounding practices, particularly in an era ofincreasing customer sensitivity to the effects of transient

voltages.IX.BIBLIOGRAPHY

The following list of references is provided toassist in locating more extensive treatment of variousspecialized topics related to grounding. It is apparent thatthis subject ha s been of interest to the distributionengineering community from the earliest days of theindustry, This bibliography is not a complete listing of allarticles written on the subject. hut each reference willprovide additional avenues for investigation by thoseinterested in pursuing each topic further.A. CodesNational E lectrical Safetv Code. 2002 Edition, (ANSI CZ),Institute of Electrical and Electronics Engineers, 2001.

2. National Electrical Code, (NFPA 70) National Fire

1.

Protection Association.B. General References an d TextsElectric U tilitv Engineering Reference Book - Distribution- Westinghouse Electric Corporation. EastPittsburgh, PA 1959.Electrical Transmission and Distribution Reference Book,4" Edition, Westinghouse Electric Corporation, EastPittsburgh, PA, 1964.

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3. Elements of Power Svstem Analvsis, by W.D. Stevenson,Jr.. M cGraw-Hill Book com pany, New York, NY, 1975.4. Distribution Svstem Protection Manual, Cooper PowerSystems, M ilwaukee, WI. 1990.

5 . Practical Utilitv Safety, by Allen L. Clapp, P E, PLS editor -Clapp Research A ssociates, Raleigh, NC, 1999.6. Downed Power Lines: Wh v Thev Cant Alwavs BeDetected. IEEE Power Engineering Society, PES-DPL-3.February 22, 1989.

Undereround Distribution Svstem Design and InstallationGuide, RER Project 90-8, National Rural ElectricCooperative Association, Arlington, VA, 1993.IEEE Guide for the Application of Neutral Grounding inElectric Utility Systems, Part I - ,C62.92.1-2OOO.IEEE Guide for the Application of Neutral Grounding inElectrical Utility Systems, Part IV-Distribution. C62.92.4-1991.

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IO. Ground Currents and the Mvth of Strav Voltas, by O.C.Seevers, Fairmont Press, Lilhum. GA , 1989.11 . Soares' Grounding Electrical Distribution Systems forSafetv, Third Edition: Wilford 1. Summers, Editor; IAEI;1986.

C. IEEE Sta nda rds a nd R US Publications1. Chapter VU. Lightning Protection and Chapters IX.Grounding.... Reference (1) REA Bulletin 83-1, dequateGrounding on Distribution Lines.

IEEE Standard 81-1983, EEE Guide for Measuring EarthResistivity. Ground Impedance and l k t h Surface Potentialsof a Ground System.IEEE Standard 80-2000, IEEE Guide for Safety in ACSubstation Grounding. Institute of Electrical andElectronics Engineers. New York, NY, 000.IEEE Standard 80-1986, EEE Guide for Safety in ACSubstation Grounding. Institute of Electrical andElectronics Engineers. New York, NY, 1986.D. Calculation MethodsAn Analog Mod el of Neutr al-to-E arth Voltag es in a Single-Phase Distribution System. Hollis Shull; LaVerne E.Stetson. P E Gerald R. Bodman, P E IEEE Rural ElectricPower Conference, CH1858-0-Cl. 1983 Rural ElectricPower Conference. Des Moines, Iowa. April 24-26, 983.Computer A nalysis of Neutral-to-Earth Potentials on RuralSystems.... Edward S. Thomas, PE; Philip 1. Monroe, EIT:IEEE No. 84 CH 1969-5. 1984 Rural Electric PowerConference Nashville, Tennessee. May 6-8, 984.

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3. Calculation of Ground Fault Current using an EquivalentCircuit and a Simplified Ladder Network. ._ . . Levey, IEEETransactions on Power Apparatus and Systems, Vol. PAS-101,No. 8, August 1982.Network Analysis of Ground Currents in a ResidentialDistribution System.... D.L. Mader, L.E. Zaffanella, IEEETransactions on Power Delivery, Vol. 8, No. I, January1993.

4.

5 . A Numerical Formulation for Grounding Analysis inStratified Soils. lgnasi Colominas, Fermin Navarrina, andManuel C asteleiro. IEEE Transactions on Power Delivery,Vol. 17, No. 2, April 2002.Analysis of Complex Grounding Systems Consisting ofFoundation Grounding Systems with External Grids. M.B.Kostic, IEEE Transactions on Power D elivery, Vol. 13, No.3, July 1998.

6.

7. Grounding System Analysis in Transients ProgramsApplying Electromagnetic Field Approach. MarkusHeimbach. IEEE Transactions on Power Delivery, Vol. 12,No. 1,January 1997.8. Simplified Two Layer Model Substation Ground GridDesign Methodology. 1. Lazzara,N. Barb eito, Petersbu rg,Florida.9. Elegant Ground Fault Solutions for Impossible Problems.David L. Swindler, IEEE Transactions on IndustryApplica tions, Vol. 37,No . 1,JanuarylFehruary 2001.10. Distribution Line P erformance with Imperfect Grounding.John M . Undrill. and R oger E. Clayton, IEEE Transactionson Industry Applications, Vol. 24, No. 5 ,S ep t emk d Oct o k r 1 9 8 8 .11. Computer Analysis of Impedance Effects in LargeGrounding Sy ste m . Ian B. Simpson, David J. Bensted,Farid Dawalihi, and Einar D. Blix, IEEE Transactions onIndustry Applications, Vol. 1A-23, No. 3, May/June 1987.12. A Complete Field Analysis of Substation Ground Grid byApplying Continuous Low Voltage$


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6. Bentonite Rods Assure Ground Rod Installation in ProblemSoils .... W m en R. Jones, IEE E Transactions on PowerApparatus Systems, Vol. PAS 99, No. 4 July I August 1980.7. A Comparison of International Residential .Groun dingPractices and Associated Magnetic Fields. Gregory B.Rauch. Gary Johnson, Paul Johnson, Andreas Stamm,Seietsu Tomita, John Swanson, IEEE Transactions onPower Delivery, Vol. 7,No. 2, April 1992.

Evaluation of Ground Resistance of a Grounding Grid ofAny Shape. Baldev Thapar, Senior, Victor Geiez, ArunBalakrishnan, Donald A. Blank, IEEE Transactions onPower D elivery, Vol. 6,No. 2, April 1991.

8.

9. Mine Power-System Grounding Research. Wils L. Cooleyand Herman W. Hill, Jr., IEEE Transactions on IndustryApplications, Vol. 24, No. 5, SeptemberlOctober 1988.10. Grounding Where Corrosion Protection is Required.Donald H. McIntosh, IEEE Transactions on IndustryApplications, Vol. IA-18, No. 6, NovemberDecember1982.11. Safe Substation Grounding - P a n I: J.G. Sverak, W.K.Dick, T.H. Dodds. R.H. Heppe. IFEE Transactions onPower Apparatus and Systems, Vol. PAS-100, No. 9, September 1981.12. Safe Substation Grounding - Part 11: J.G. Sverak, R.H.Benson. W.K. Dick, T.H. Dodds, D.L. Garret, J.E.Idzkowski, R.P. Keil, S.G. Peter, M.E. Ragen, G.E. Smith,R. Verma and L.G. Zukerman. IEEE Transactions onPower Apparatus and Systems, Vol. PAS-101, No. 10,

October 1982.13. Impulse and Alternating Current Tests on GroundingElectrodes in Soil Environm ent. William K. Dick, HarveyR. Holliday, IEEE Transactions on Power Apparatus &Systems, Vol. PAS-97, No . I , JanuaryIFebruary 1978.14. The Use of Concrete-Enclosed Reinforcing Rods asGrounding Electrodes, Fagan, E.J. and Lee, R.H., IEEETransactions on Industry Applications, Vol. IGA-6, No. 4,July I August 1970.15. General Considerations in Grounding the Neutral of PowerSystems, by H.H. Dewey, A.I.E.E., Pittsburgh, PA April24-26, 1923.16. Grounding of High Potential Systems, by 1.D. Niles,Electrical World and Engineer, April 12, 1902.17. 15 August 1973 Draft of NESC Pan 2 1977 Edition,Institute of Electrical and Electronics Engineers; New York,New York, 1973.

18. Impulse and 60-cycle Characteristics of Driven Grounds,P.L. Bellaschi, NEE Transactions. Vol. 60, 941.19. Impulse and 60-cycle characteristics of Driven Grounds-II,P.L. Bellaschi, R.E. Armington, A.E. Snowden. NEETransactions, Vol. 61, 1941.20. Ground Current Magnetic Field Study, Research Report EP90-50, N.Y. Institute of Technology, Empire State ElectricEnergy Research Corporation. January 1993.

F. EquipmentProtection1. Full Scale Lightning Surge Tests of DistributionTransformers and Secondary Systems.... Gary L. Goedde,Roger C. Dugan, Lawrence D . Rowe, IEEE Transactions onPower Delivery, July 1992, Volume 7,No. 3.

Susceptibility of Distribution Transformers to Low VoltageSide Lightning Surge Failure .... C.J. McMillen, C.W.Schoendube: D.W. Caverly, IEEE Transactions on PowerApparatus and Systems, Vol. PAS-101, No. 9, September1982.

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3. A Guide to the Application of Surge Arresters forTransformers Protection .... Dennis A. Zolar, IEEETransactions on Industry Applications, Vol. 1A-15. No . 6, November I December 1979.4. Distribution Surge Arrester Behavior Due to LightningInduced Voltages.... Shigeru Yokoyama, IEEETransactions on Power Delivery, Vol. PWRD. No. 1,January 1986.

Distribution Arrester Failures Caused by Lightning CurrentFlowing from Customer s Structure into DistributionLines.... K. Nakada, T. Wakai, H. Taniguchi, T. Kawabata,S. Yokoyama, T. Yokota, A. Asakawa, IEEE Transactionson Power Delivery, Vol. 14,No . 4, October 1999.

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6. Lightning Protection of Distribution Lines .... T.E..McDermott, T.A. Short, J.C. Anderson, I EEETransactionson Power Delivery, Vol. 9, No. I , January 1994.Reduction in Distribution Transformer Failure Rates andNuisance Outages Using Improved Lightning ProtectionConcepts .... Charles W. Plummer, Gary L. Geodder. PE,Elmer L. Pettit, Jr. PE, Jeffrey S. Godbee, Michael G.Hennessey, PE, 94 TD038, T-PWRD April 1995. IEEETransactions on Power Delivery, Vol. 10,No. 2, April 1995.Distribution Lightning Protection Past, Present, Future ....Dee C. Panish, Carroll Electric Membership Corporation.Reference: IEEE Rural Electric Conference Paper No. CH1654-3 1981. 1981 Rural Electric Power Conference.Atlanta, Georgia. April 26-28, 1981.

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9. Protection of Underground Systems Using Metal-OxideSurge Arresters. ... W.D. Niehubr, IEEE Rural ElectricPower Conference Paper No. C H 1654-3 1981. 1981 RuralElectric Pow er Conference. Atlanta, Georgia. April 26-28,1981G. LightningEstimating Lightning Performance of Transmission Lines I1- Updates to Analytical Models .... IEEE Working GroupReport. 92 SM453-1 PWRD, T-PWRD July 1993 - IEEETransactionson Power Delivery. Vol. 8,No. 3, July 1993.

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2. Lightning-induced Voltage on an Overhead WireDependent on Ground Conductivity.. .. Masaru Ishii, KojiMichishita, Yasuji Hongo, Syujiro Oguma. 93 WM 092-7PWRD, T-PWRD January 1994.Laboratory Studies of The Effects of M ultipulse LightningCurrents on Distribution Surge Arresters.. ..M. Darvenizaand D.R. Mercer, 92S M 355-8 PWRD. T-PWRD July 1993.

4. Lightning-Induced Voltages on Overhead Power Lines.Part I.... C.A. Nucci, Working Group 33.01 (Lightning).(CIGRE) E lectra No. 161. August 1995.Lightning-Induced Voltages on Overhead Power tines.Part 11..._C.A. Nucci, Task Force 33.01.01 (lightninginduced voltages) of Study Committee 33. Electra No. 162,October, 1995.

6. Frequency of Distribution Arrestor Discharge Currents Dueto Direct Strokes.... Gordon W . Brown, Steven Thunander,IEEE T ransactions on Power Apparatus and Systems, Vol.PAS-95, No. 5, September I October 1976.H.Transformer Grounding According to the National ElectricCode .... Mike Holt, Power Quality Assurance - July IAugust 1998.Transformer Grounding and Transferred Earth Potentials.._ .Tom Shaughnessy, Power Quality Assurance - September /October 1998.The Foundations of Good Grounding .... Tom Shaughnessy.Power Quality A ssurance - January / February 1998.Types of G rounding Systems.. ..Tom Shaughnessy, PowerQuality Assurance - July I August 1998.

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Power Quality and Com municatio n Systems1.

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5. Lightning Can. Teach Important Lessons Ahout PowerProtection .... Mark Mull and George Bowden, PowerQuality Assurance - July/ August 1998.

6. Understanding the Proliferation of Power Grounding andProtection Standards.. .. William Bush, Power QualityAssurance - January I February 1994.Grounding-Part 1 - Basic Principles.... Mark W aller. PowerQuality. Premier 111 1990.Industrial System G rounding for Pow er, Static, Lightningand Inshum entation, Practical Application s. Philip W.Rowland, IEEE Transactions on Industry Applications, Vol.31. No . 6,NovemberDecemher 1995.Discussions of Industrial System Grounding for PowerStatic, Lightning and Inshum entation. Richard Singer.IEEE T ransactions on Industry Applications, Vol. 32, No . 5,September/October 1996.I. S t r a y VoltageSource of Stray Voltage and Effect on Cow Health andPerformance.... R.D. Applem an and R.J. Gu stafson, Journalof Dairy Scien ce, August 23,1984.Techniques for Coping with Stray Voltages .... Robert J.Gustafson, Harold A. Cloud, Vemon D. Alhertson,Agricultural Engineering - December 1984.

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3. Response of Dairy Cattle to Transient Voltages andMagnetic Fields.... Douglas I. Reinemann, LaVerne E.Stetson, Nellie K. Laughlin, 1994 I EEE Rural ElectricPower C onference Colorado Springs, Colorado - Paper 94c 5 .Neutrd-to-Eat?h Voltage and Ground Current Effects inLivestock Facilities.... R.J. Gustafson, V.D. Alhertson.IEEE T ransactions on Power Apparatus and Systems, Vol.PAS-101, No. 7, July 1982.Stray Voltage: Sources and Solutions....Truman SurhrookP E Norman Reese, P E Angela Kehole, IEEE RuralElectric Power Conference Paper No. 84CH 1969-5 B5 .1984 Rural Electric Power Conferen ce. Nashville,Tennessee, May 6-8, 1984.Stray Voltage Update 97 ....Douglas J. Reinemann. PhD,LaVerne E. Stetson, Daniel M. Dasbo and Mark A. Cook,1997 IEEE Rural Electric Power Conference Minneapolis,Minnesota, April 20-27. 1997.Understanding and Dealing with Stray Voltage in LivestockFacilities. Robert J. Gustafson, Reference: IEEE RuralElectric Power Conference, Paper No. CH 126-1 1985. (85C2.) 1985 Rural Electric Power Conference, Springfield,Illinois. April 28-30, 1985.Stray Voltage on the Dairy Farm. ._ . ichard S. Seeling, PE,IEEE Rural Electric Conference. Paper No . 80 C4 CH 1532-

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I 1980. 1980 Rural Electric Power Conference, Rapid City,South Dakota. April 27-29, 1980.

AwnomEdward S. Thomas, PE (SM) holds a bachelor of sciencedegree from North Carolina State University. He hasworked in the electric distribution field since 1964 withDuke Power, Piedmont EMC and engineering consultingfirms. Thomas is president of U tility Electrical Consultants,PC in Raleigh, NC, a firm providing consulting engineeringservices to utilities and other owners of medium and highvoltage systems. Thomas is a registered engineer in NorlhCarolina and ten other states. He was the editor of a manualon underground system design, the author or principal co-author of five previous papers on distribution systems andauthor of a recent analysis of distribution transformerprotection methods.John B. Dagenhart, P.E. (SM) is an Associate of ClappResearch Associates, P.C., and is lead engineer for m any ofCRAs electrical projects. He has investigated over 100accidents. John is chair of NESC Subcommittee 2 onGrounding Methods and serves on the IEEE/NESC LectureTeam. He regularly presents DANESCm Seminars for CRAclients, and is an authorized OSHA con struction regulationsinstructor.Mr. Dagenhart is a contributor to McGraw-Hills StandardHandbook for Electrical Engineers, an associate editor ofthe DANESC UPDATE Newsletter; provided researchfor the NESC Handbook; co-authored and edited PowerSystems Disturbances Manual for Duke Power Company;contributed to the upcoming E E E E merald Book Poweringand Grounding Sensitive Electronic Equipment; andauthored or co-authored anicles on electrical power qualityissues and both the National Electrical Safety Code (NESC)and the National Electrical Code (NEC ).Allen L. Clapp, P.E., P.L.S. (SM) is President of ClappResearch Associates, P.C., Consulting Engineers. The fmserves over 250 utilities and industries. Allen has beeninvolved in the design and evaluation of electric supply andcommunication facilities for over 35 years and hasinvestigated over 500 accidents. He has testified beforecourls and commissions for over 30 years. His rich andvaried knowledge of investigating and litigating utilityaccidents is shared with seminar panicipants.Mr . Clapp is a member (Chair 1984-1993) of the NationalElectrical Safety Code Committee and a member of thefollowing subcommittees: Interpretations (past Chair);Strengths and Loadings (Secretary); Clearances (pastActing Secretary); and Coordination (Chair and PastSecretary). He has served continuously on NESC technicalsubcommittees since 1971 and ha s chaired a number of

special working groups. Allen also chairs ANSI 2535.2Subcommittee on Environmental and Facility Safety Signs.Allen Clapp is editor of the N ESC Handbook pu blished bythe Institute of Electrical and E lectronics Engineers. He alsoedits and publishes the DANESC UPDATE newsletterand Practical Utility Safety and is a conuihutor to McGraw-Hill s Standard Handboo k for Electrical Engineers.Richard A. Barber (M)holds a Bachelor of Science degreein electrical engineering from the University of Illinois. Hehas worked in the electric utility industry since 1986 andhas 12 years of engineering, operations. and managementexperience working for rural electric cooperative andmunicipal electric systems. Richard presently works forUtility Electrical Consultants, PC. in Raleigh, NC where heis engaged in special projects.

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