Grounding & Bonding-Temporary Power Generation And .
Grounding & Bonding;Temporary Power Generationand Electrical DistributionBased on the 2017National Electrical CodeJanuary 19, 2019By: Steven S. Gibson, CESCP“Grounding, bonding and the creationof an effective ground fault currentpath is the backbone of electrical safetyand shock prevention in temporarypower generation and electricaldistribution system installations”
Table of ContentsAbstractThe Grounding & Bonding SystemSafetyConductor Identification; Major Aspect of SafetyComing to terms with NEC Article 250 Grounding & BondingGrounding Electrode (Ground Rod Installation)Separately Derived SystemGrounding Portable and Vechicle Mounted GeneratorsMultiple Sources of Supply (12 ft. Rule)Ground-Fault Current & Overcurrent ProtectionAvailable Short-Circuit CurrentInterrupting Protection Rating (Ampere Interrupting Capacity)Special Consideration for Grounding GeneratorsConclusionAuthor BiographyReferences11235811121313141516181818
Grounding & Bonding; Temporary Power Generation and Electrical DistributionAbstractThe subject of grounding and bonding can beconfusing this is especially true for portable andvehicle (trailer) mounted generators used in thefield to supply temporary/emergency power forapplications such as construction, industrial, specialevents and emergency power during disasters. Theterms Grounding, Ground, Grounded, Bonding, andGround Fault Current Path and their respectivepurpose within the electrical system are frequentlyintertwined and used incorrectly. Many fieldtechnicians and electricians mistakenly interchangethese terms which further confuses the conceptwhich can lead to improper and unsafe installationof temporary electrical systems.The main reason for the grounding and bondingsystem is safety of personnel and property.Improper installation of the grounding and bondingsystem can result in accidental injury or death fromelectrocution,improper operation of t, and extensive equipment damage andpossibly fires.This paper using simple terms and examples willdiscuss the grounding and bonding system as itrelates to both permanent and temporary electricalsystem installations, specific components of thesystem, there function and the requirements of theNational Electrical Code (NEC). This paper will alsodiscuss NEC terminology, relationship betweeneffective low impedance ground fault current pathand the operation of the overcurrent protectiondevice, separately derived systems, available shortcircuit current, the relationship of the grounding &bonding system to safety, and hopefully clear-upany misunderstandings or confusion surroundinggrounding and bonding of generators.The Grounding & Bonding SystemThe term ground and grounding are frequentlymisapplied. Some refer to ground as a commonreference point within the electrical system or as1IEEE Std 142 (2007) IEEE Green Bookthe return path for current flow to operate theovercurrent protection device if a fault currentevent should occur which is not what the ground isintended for. The terms ground, grounding andgrounded as defined by the National Electrical Coderefer to earth or a connection to earth.The purpose of system grounding is to intentionallyconnect the neutral point of an electrical system andthe equipment grounding conductor to earth in amanner that controls voltage with respect to earthto within predictable limits. 1 Grounding(connecting) to earth through an approvedgrounding electrode system (example; ground rod)as outlined in NEC 250.52(A)(2) through (A)(8)serves an important function within the electricalsystem. The electrical system is intentionallygrounded (connected) to earth in a specific mannerto limit the voltage imposed by direct or indirectlightning strikes, line surges, or unintentionalcontact with higher voltage lines and the earthconnection is also used to stabilize the voltage toearth during normal operations 250.4(A)(1).For practical electrical systems the earth or groundpotential is usually considered zero or near zero.When there is a potential difference in chargesbetween two points in an electrical circuit expressedin volts current flow in the circuit can occur.Connecting to earth and creating a zero reference orzero potential difference eliminates touch potentialbetween conductive surfaces and the earth intheory but is still based on the contact resistance ofthe earth. 2Earthing or grounding (connecting) to earth is notintended to be used as a ground- fault current pathfor fault detection and/or as a means of operatingthe overcurrent protection device (circuit breaker orfuse) to clear faults. Earth is conductive to a certainextent but because of soil resistivity it should neverbe considered as an effective path for ground-faultcurrent to effectively operate or trigger an2ProSpex (2006) Electrical System Bonding and Grounding1
Grounding & Bonding; Temporary Power Generation and Electrical Distributionovercurrent protective device (OCPD) if a shortcircuit or line-to-ground should occur 250.4(A)(5).The purpose of bonding is to join metallic partstogether to form a conductive path that ensureselectrical continuity and has the capacity to conductsafely any current likely to be imposed. Bondingmetallic parts together equalizes any potentialdifference or touch potential between metalsurfaces to eliminate the flow of current and iteliminates any buildup of static charges that havethe potential to cause damage to sensitiveequipment. All metal surfaces, enclosures, metalstructures that are likely to come in contact with orbecome energized if a fault occurs should bebonded together and to the grounded (neutral)conductor and equipment grounding conductor toform a path for fault current to travel back to source.The bonding of metal components is not designednor intended to carry current under normaloperating conditions, but it must be able to safelydo so in the event of a short circuit or ground-faultcurrent is imposed on it. 3Since all metal parts are bonded together to createconductivity and continuity in the event of a groundfault the current will try to flow back to earth orsupply source though the least path of resistance.The equipment grounding conductor is a wirespecifically sized that connects non-current carryingmetal parts such as enclosures, metal frames ofequipment, appliances, motors, etc. back to thegrounded (neutral) conductor and/or groundingelectrode conductor or both. The function of theequipment grounding conductor is to intentionallycreate an effective low impedance path to allowfault current to travel back to the electrical sourceto properly operate the overcurrent protectivedevice to clear the fault without causing majordamage to the system. According to informationalnote 1# Article 100 of the NEC the equipmentgrounding conductor can also perform the functionof bonding.434ProSpex (2006) Electrical System Bonding and GroundingArticle 100 (2017) National Electrical CodeFigure 1SafetyOften installation of power generation andtemporary power distribution equipment (Figure 1)on construction sites, industrial facilities and specialevent venues are viewed by electricians andtechnician as “Anything Goes”. Temporary electricalinstallations on construction sites are commonly themost cited by OSHA during routine and focusedinspections. Three of the 10 most cited violations inbuilding construction are related to electricalrequirements: 1926.451 General Requirements,1926.405 Wiring Methods, Components andEquipment for General Use, and 1926.404 WiringDesign and Protection.5 See figure 1-A for anexample of temporary electrical system.Figure 1-AElectricity doesn’t distinguish between permanentor temporary installations that is why the sameinstallation practices and workmanship apply to5Wheeler, W.L. (2016) Temporary Electrical Power, Keeping itSafe!2
Grounding & Bonding; Temporary Power Generation and Electrical Distributionboth with a heavy emphasis on temporary becausethe electrical system is more exposed to the public.Grounding, bonding and the creation of an effectiveground fault current path are critical aspects of theelectrical protective system. Bonding of metallicparts, enclosures and the equipment groundingconductor (which also serves as a means of bonding)create an effective ground fault current pathcoupled with the overcurrent protection systemclears potentially dangerous shorts circuits andground-faults which can prevent and/or minimizethe potential for shock, electrocution and fires fromunintentional dangerous voltages on metallic partsin contact with the temporary electrical system.All metallic components and parts that can come incontact with or are part of the temporary electricalsystem are bonded together to create conductivityand continuity. The equipment groundingconductor is connected between the equipmentenclosures, frames, appliance, motors etc. back tothe grounded conductor (neutral) to intentionallycreate a low impedance fault current path topromptly operate the overcurrent protection devicein the event a ground fault should occur.The proper operation of the overcurrent protectiondevice when a fault occurs is dependent on thecurrent in the circuit rising quickly and have a highenough value to be detected by the OCPD so that itcan properly operate and promptly open to removethe voltage in the circuit.When considering system short-circuit protection itis important to understand the maximum availablefault current that can flow in a circuit to properlyoperate the overcurrent device. Generally, theamount of fault current available in the circuit of atemporary electrical system is based on theimpedance of the supplying transformer and/or thereactance of the generator. 6 Please note; higheravailable fault current also means higher arcingcurrent which has a direct impact on the level of PPE6Pfeiffer, J. (2001) Principles of Electrical Groundingrequired by personel working near or on energizedtemporary electrical systems.Example Figure 1-BThe preceding diagram demonstrates a shortoccurring between a phase conductor and the frameof the motor. The grounding system was improperlyinstalled, the neutral is grounded to earth but it isnot connected to the equipment groundingconductor (missing system bonding jumper). Thereis not an effective low resistance path back to sourceto clear the fault, the frame remains energized sinceearth is not an effective ground fault-current path.The worker touches the frame and completes thepath when his knee touches the ground (earth)which causes current to flow though the worker dueto the potential difference. The current flowingthrough the worker to earth, back to the groundrod, and then to source is not high enough tooperate the overcurrent device. In this exampleimproper installation of the bonding jumper causesa shock and possibly electrocution to the worker.Conductor Identification;Major Aspect of SafetyA very important safety aspect of the installation oftemporary electrical distribution systems is theproper identification of conductors. Improperconductor identification can lead to metal framesand enclosures becoming energized, Line to groundor line to line shorts which create the potential forshock, electrocution, arc flash and extensivedamage to equipment.3
Grounding & Bonding; Temporary Power Generation and Electrical DistributionPer 200.6(A) the insulated grounded (neutral)conductor 6awg or smaller shall be identified by oneof the following means;(1) Feeders supplied from more than onevoltage system, each ungrounded conductorat all termination, connection and splicepoint must be identified by phase or line andsystem, in accordance with (a) and (b)(1) Continuous white outer finish(2) Continuous grey outer finish(a) Identified by color coding, marking tape,tagging, or other means approved by theauthority having jurisdiction.Per 200.6 (B) the grounded conductor (Neutral)Sizes 4 AWG or larger shall be identified by one ofthe following means; 7(b) Such identification must be documented ina manner that is readily available.(1) Continuous white outer finish(2) Continuous grey outer finish(3) Three continuous white or grey stripesalong the conductor entire length(4) At time of installation, grey or whitemarking at its termination. Marking shallencircle the conductor or insulation.Grounded conductor of different systems such asone system rated at 480V suppling power totemporary high voltage lighting equipment andanother system rated at 208V suppling temporarylow voltage distribution installed in proximity ofeach other, bundled together or in the same cableramp shall have the grounded conductor identifiedand distinguishable by system 200.6(D). 8 Example:480V system the neutral marked with grey phasetape and the neutral of the 208V system markedwith white phase tape.Equipment grounding conductor 6awg or smallermust have a continuous outer finish either green orgreen with one or more yellow stripes per 250.119.9Insulated equipment grounding conductor 4 AWGor larger can be permanently reidentified with greenmarking tape at the time of installation at everypoint where the conductor is accessible and at theconductor ends per 250.119(A).10Using marking tape, each conductor should betaped 3” to 6” for greater visibility.Industry best practice color code system for powerand lighting conductor identification: 120/240V single-phase — black, red, andwhite 120/208V, 3-phase — black, red, blue, andwhite 120/240V, 3-phase — black, orange, blue,and white 277/480V, 3-phase — brown, orange,yellow, and gray; or, brown, purple, yellow,and gray.When installing temporary conductors in the field itis important to clearly mark the conductors prior toinstallation to eliminate incorrectly marking theends of the conductors after installation which cancause a short circuit when system is energized.Example: 50’ - 4/0, one end marked green and theother marked orange.Per 215.12 (C) Ungrounded (Phase) Conductorsshall be identified by one of the following means;Comment: Inspectors view flexible cords and cablewith Camlok connectors with caution because theyare not attachment plugs or receptacles.11 Thesetypes of single cables are required to be 2AWG orlarger and rated for extra-hard usage see Article 400for flexible cords and cable. When using Camlok710811Article 200 (2017) National Electrical CodeArticle 200 (2017) National Electrical Code9Article 250(2017) National Electrical CodeArticle 250 (2017) National Electrical CodeSampson, Marcus (2012) Electrical Inspections forCarnivals, Fairs and Traveling Shows4
Grounding & Bonding; Temporary Power Generation and Electrical Distributioncable pay special attention to Article 525.22(D) andthe rules of 530.22. 12 Installation and use of thesetypes of cords and cable as a temporary wiringmethod require protection from physical damagesuch as the use of cable ramps per 525.20(G).When using temporary wiring methods that includethe use of flexible cords and cable it is a requirementupon completion of the installation that thecontinuity of the equipment grounding conductorbe verified per 525.32 to provide assurance ofconductivity and continuity between the source andequipment, frames, enclosures and metal surfacesto ensure touch potential is eliminated and acomplete path back to source is established for faultcurrent to travel, rise quickly and properly operatethe overcurrent protection device if a fault shouldoccur. This is especially important since most ofthese types of venues and temporary electricalsystems installations are exposed to the public.Prior to any installation of electrical equipmentsupplies power to special event venues and similarevents it is highly recommended the technician(s),electricians or project management becomefamiliar with the NEC, grounding, bonding andespecially Article 525 to ensure proper installationof equipment while always keeping public safety inmind.low impedance path back to source, to avoid anyappreciable potential difference between anyseparate points (250.4(A)(3).14 Bonding should bedesigned in a way that provides a low impedancepath for fault current to travel back to source toproperly operate the OCPD.The safety aspect of effective bonding is to minimizeor eliminate potential difference between noncurrent carrying metallic surfaces within theelectrical system. Bond provides zero reference toeliminate touch potential in case a fault shouldoccur.Bonding Jumper, System. A conductor installedbetween the grounded (neutral) conductor and theequipment grounding conductor at a separatelyderived system (generator or transformer) toensure electrical continuity and has the capacity toconduct safely any fault current likely to beimposed. The system bonding jumper is sized perTable 250.102(C)(1) and based on the largestungrounded phase conductor. Pay close attentionto the notes listed at the bottom of the table.Coming to terms with NEC Article 250Grounding & BondingBonded. Non-electrical metallic parts connected toestablish electrical continuity and conductivity.13The joining of metallic parts together to form anelectrically conductive path.Bonding. Is a method which all electricallyconductive materials and metallic surfaces ofequipment and structures not normally intended tobe energized are effectively interconnectedtogether normally through a conductor to provide aComment; The primary function of the systembonding jumper is to complete the connection(path) between the source grounded conductor andthe equipment grounding conductor at theseparately derive system so phase-to-ground faultcurrent can travel back to source to properlyoperate the OCPD and clear the fault .15 Intemporary power distribution projects supplied by a1214Sampson, Marcus (2012) Electrical Inspections forCarnivals, Fairs and Traveling Shows13Article 100 (2017) National Electrical CodeWaterer, F. (2012) Effective bonding, grounding: Thebackbone of electrical safety15EP Editorial Staff (2011) Bonding and Grounding Issues inPower Distribution Systems5
Grounding & Bonding; Temporary Power Generation and Electrical Distributionportable or vehicle (trailer) mounted generator thebonding jumper connecting the neutral to theequipment grounding conductor and to frameand/or earth is typically located in the generatorenclosure at the output lug panel. The bondingjumper is part of the effective ground-fault currentpath to allow fault current travel back to source toproperly operate the overcurrent protection deviceto clear the fault (refer to figure 1-C#). The bondingjumper should be installed in one location such asthe main distribution panel or at the power source(generator or transformer secondary). It shouldnever be located at both locations or on the loadside of the distribution panel. Multiple neutral toequipment grounding conductor bonds can createsa parallel path for fault current to travel which maynot properly operate the OCPD and may subject thesystem to objectionable current.Effective Ground - Fault Current Path. Electricalequipment, wiring and other electrically conductivematerial likely to become energized shall beinstalled in a manner that creates a low impedancecircuit that facilitates the proper operation of theovercurrent device. The low impedance path shallbe capable of safely carrying the maximum groundfault current likely to be imposed on it from anypoint on the wiring system where the ground faultmay occur back to the electrical supply source.250.4(A)(5).16 See Figure 2#.An intentionally constructed, low-impedance pathdesigned to carry ground-fault current from thepoint of the line to ground (frame) fault on the wiringsystem back to the supply source. This lowimpedance path based on ohm law, when a faultoccurs will create a high enough current surge in thesystem to be detected and facilitate the operation ofthe overcurrent protection device. The “earth” shallnot be considered as an effective ground-faultcurrent path 250.4(A)(5)Temporary Power Distribution systemEffective Ground-Fault Current PathTerminalLugsGenerator enclosureGround FaultDistributionPanelMotor LoadNeutralPointNNSystem BondingJumperGroundedConductorEGCGrounding Electrode ConductorGrounding Electrode driven into the earthLow Impedance fault current pathfor L-G fault current to travel back tosource to facilitate the operationof the overcurrent device250.4(A)(5)Figure 2Generator undFaultLoad15ANeutralPointNNBroken EGC4.8 AVVΩOFFEnclosureAAVΩAC OMBoth the generator and distribution panel are connected to ground (earth) through a ground rod,if the contact resistance of the earth and the ground rod is 25 ohms not enough fault current willbe generated to operate the over current device.Figure 2-AExample; Figure 2-A the energized conductor isshorted to the enclosure unfortunately, theequipment grounding conductor is broke so the onlyreturn path for fault current to travel back to sourceis through earth. If the contact resistance throughearth to the grounding electrodes is 25 ohms, thenmathematically the fault current generated is nothigh enough to properly operate the 20Aovercurrent device. Contact resistance of the groundingelectrode to earth is 25Ω ohms. Ohms law (I E/R)120V / 25Ω 4.8 amps.16Article 250 (2017) National Electrical Code, page 70-1046
Grounding & Bonding; Temporary Power Generation and Electrical DistributionThe amount of ground fault current generated is notenough magnitude to operate the 20-amp circuit breakerlocated in the distribution panel.Temporary Power Distribution systemGeneratorCircuit BreakerS y s te m B o n d in g Ju m p e rGrounded (Neutral)Ground-FaultL-G 120V200'12AWGLoad.402 ohmsDistributionPanel20AL2L1XoEnclosureL314 9VVAΩOFFAEGC200' 12awg.402 ohmsAVΩAGen Ground terminalNEC Ch. 9, Table 812Awg 2.01 ohms per 1000'2.01 / 1000 .00201 per ft'.00201 x 200' .402 ohmsCOME A Fault CurrentZ120V 149.2A.804.402 .402 .804 ohmsFigure 2-B (Example Only)Figure 2-A demonstrates mathematically earth isnot an effective ground- fault current path. Figure 2B demonstrates the effectiveness of creating a lowimpedance fault current path back to source. Basedon the impedance of the circuit 149 amps of faultcurrent is generated when the ground-fault occurswhich is enough to operate the 20A single polebreaker.The illustration is an example, for a more detailmethod of calculating system short-circuit currentrefer to; Bulletin EDP-1 (2004) EngineeringDependableProtection Foran ElectricalDistribution System, Part 1, A Simple Approach toShort- Circuit Calculations. Cooper-Bussmann.Ground. NEC defines ground as the earth.17 IEEE 142defines ground as a conducting connectionintentional or accidental between an electricalcircuit or equipment and the earth, or to some otherbody that serves in place of the earth.18Comment: A good example of a conductive bodythat serves in place of the earth is a portable orvehicle (trailer) mounted generator. Under specificcondition of uses NEC 250.34 permits the generatorframe to be used in place of earth.Ground Fault. An unintentional electricallyconductive connection between an ungrounded(phase) conductor and the normally non-currentcarrying conductors, metal parts of enclosures,equipment, or earth.19Ground-Fault Circuit Interrupter (GFCI) A deviceintended for the protection of personnel thatfunctions to deenergize a circuit within anestablished period when a current to groundexceeds the value established for a Class A device. AClass A device trips when the current to groundexceed 5ma or higher. For information of GFCI seeUL 943, Standard for Ground-Fault CircuitInterrupters.Comment: All 125-volt, single-phase 15-, 20-, and30-ampere receptacles that are not part of thepermanent wiring of a building or structure and arein use by personnel shall have ground-fault circuitinterrupter protection 590.6(A)(1). All receptacles inused for outdoor use by personnel shall be GFCIprotected. If the GFCI and the branch circuitsupplying the receptacle utilize a portable cord theGFCI shall be listed, labeled and identified forportable use 525.23(D).Grounded (Grounding) Connected to ground (earth)or to a conductive body that extends the groundconnection.20Grounded Conductor. A system or circuit conductor(normally the neutral) that is intentionally grounded(Connected to Earth).21 The grounded conductor issized in accordance with Table 250.102(C)(1).17201821Article 100 (2017) National Electrical CodeIEEE Std 142 (2007) IEEE Green Book19Article 100 (2017) National Electrical CodeArticle 100 (2017) National Electrical CodeArticle 100 (2017) National Electrical Code7
Grounding & Bonding; Temporary Power Generation and Electrical DistributionU(L1)GeneratorWindingsneutral directly connected to ground (earth)without inserting any resistors or impedancedevices between the system and earth.24V(L2)277VNeutralPoint480VSolidly Grounded277VTerminalLugsGenerator enclosureW(L3)DistributionPanelNeutralPointNFigure 3Neutral Conductor. The conductor connected to theneutral point of a system that’s intended to carrycurrent under normal conditions.22 See Figure 3#.Grounding Conductor, Equipment (EGC). Theconductive path(s) that provides a ground-faultcurrent path and connects normally non-currentcarrying metal parts of equipment together and tothe system grounded conductor or to the groundingelectrode conductor or both.Article 100definitions, Informational note No.1: It is recognizedthat the equipment grounding conductor alsoperforms bonding.23 The equipment groundingconductor is sized per Table 250.122 and is based onthe size of the overcurrent device.Example: A 6/4 SOO 50A spider box cord, the greengrounding wire is actually a bond wire that bondsthe metal frame of the spider box back to source toensure there are no potential difference. Thegrounding wire does not carry current under normaloperating conditions. Its primary purpose is to carryelectrical current only under short circuit or groundfault conditions that would be potentiallydangerous. The equipment grounding wire serves asthe primary path for the fault current to flow backto source to properly operate the OCPD and removedangerous voltages from unintentional energizationof metallic surfaces, frames or electrical enclosures.NGroundedConductorSystem BondingJumperEGCGrounding Electrode ConductorGrounding Electrode driven into the earthFigure 4Figure 4-ASolidly Grounded System. An electrical powersupply system such as a generator that has theGrounding Electrode. A conducting object throughwhich a direct connection to earth is established.25Example: Metal underground water pipe, concreteencased electrode (rebar), ground ring, groundplate and ground rod. Most common electrode used222423Article 100 (2017) National Electrical CodeArticle 100 (2017) National Electrical Code, p.70-3725Csanyi, E. (2015) When to use a solidly grounded system?Article 100 (2017) National Electrical Code8
Grounding & Bonding; Temporary Power Generation and Electrical Distributionwith temporary generators is the ground rodelectrode.Ground rod installation requirements; 250.53(G)See Figure 5#Ground Rod Installation250.53 (G)Grounding Electrode Conductor6 AWG Copper - 250.66(A)2 1/2 ftMinimum8 ftMin.45Figure 5#Grounding Electrode Conductor. A conductor usedto connect the system grounded conductor or theequipment to a grounding electrode or to a point onthe grounding electrode system.26 Groundingelectrode conductor is sized in accordance with250.66.Comment: Pay close attention to 250.52 GroundingElectrodes, 250.53 Grounding Electrode SystemInstallation and 250.66 Size of Alternating-CurrentGrounding Electrode Conductor. These articlesintertwine with each other and can bemisinterpeted.Example 1#: Grounding electrode conductor is sizedper table 250.66 except as permitted in 250.66(A)through (C). 250.66(A) If the grounding electrodeconductor connects to a rod, pipe or plate electrodeand does not extend to other types of electrodesthat require larger conductors then the groundingelectrode conductor shall not be required to belarger than a 6 AWG copper conductor.(A)(8) which basically means when a generator isrequired to be grounded (connected) to earth thenyou have to install two or more ground rods. Pleaseread the exception listed at the bottom of250.53(A)(2) “Exception: If a single rod, pipe, orplate electrode has a resistance to earth of 25 ohmsor less, the supplemental electrode shall not berequired.”The complexity surounding earth grounding, whatcostitutes a good ground and what resistance valuesare exceptable has been discussed and studied foryears. Ideally a ground should achieve a value ofzero ohms. NFPA and IEEE have recommended acontact resistance of 5 ohms or less. 27 NEC250.53(A)(2) Exception – if a grounding electrodehas a resistance to earth of 25 ohms or less than asupplemental rod is not required. The reference to25 ohms is what the NEC uses as it maximumresistance value,some applications such astelecommunication may require less than 10 ohmsfor sentitive equipment.Establishing an effective earth grounding electrodesystem that has a low resistivity can be complicatedand it effectiveness is depedant on soil resistivitywhich varries based on soil mediums, moisurecontent and disolved salts.Using a standard multimeter to measure contactresistance from the grounding electrode to earth toprove the contact resistance is less than 25 ohms isnot an effective means of measuring soil resistivity.Example 2#: 250.53(A)(2) a single rod, pipe, or plateelectrode shall be supplemented by an additionalelectrode of a type specified in 250.52(A)(2) throughTypically, soil resistivity is measured utilizing theWenner Four-Pin Method which uses a groundresistance meter (Figure 5-A).28 Four metal pins areplaced in contact with the ground in a straight lineand equally spaced. A constant current is theninjected through the ground via the meter and theouter two electrodes labeled C1 and C2. Thepotential drop is then measured across the innertwo electrodes labe
Mar 26, 2019 · Coming to terms with NEC Article 250 Grounding & Bonding Grounding Electrode (Ground Rod Installation) Separately Derived System Grounding Portable and Vechicle Mounted Generators Multiple Sources of Supply (12 ft. Rule) Ground-Fault Current &am
Grounding Study and Analysis: Substation Grounding Practices Grounding Concepts - GPR and Touch Potential AEP Innovative Grounding Study Methods Grounding Installation: Traditional Approach and Challenges Grounding Application and Installation Change Management Testing: Grounding Integrity Testing Conclusion and .
Article 250.1 Scope. Article 250 is organized into 10 different parts that deal with specific requirements with regards to bonding and grounding. The specific parts are as follows: (I) General (II) System Grounding (III) Grounding Electrode System and Grounding electrode Conductor (IV) En
B. Grounding - If the removal of a grounding or bonding connection in the normal power source equipment interrupts the grounding electrode connection to the alternate power source(s), a warning sign at the normal power source equipment is required stating: WARNING. SHOCK HAZARD EXISTS IF GROUNDING. ELECTRODE CONDUCTOR OR BONDING JUMPER
Modern Chemistry 1 Chemical Bonding CHAPTER 6 Chemical Bonding SECTION 1 Introduction to Chemical Bonding OBJECTIVES 1. Define Chemical bond. 2. Explain why most atoms form chemical bonds. 3. Describe ionic and covalent bonding. 4. Explain why most chemical bonding is neither purely ionic or purley 5. Classify bonding type according to .
comparing with Au wire bonding. Bonding force for 1st bond is the same range, but approx. 30% higher at 2nd bonding for both Bare Cu and Cu/Pd wire bonding but slightly lower force for Bare Cu wire. Bonding capillary is PECO granular type and it has changed every time when new cell is used for bonding
from electric shock. Bonding and earthing are often confused as the same thing. Sometimes the term Zearth bonding is used and this complicates things further as the earthing and bonding are two separate connections. Bonding is a connection of metallic parts with a Zprotective bonding conductor. Heres an example shown below.
NEC Table 250.122 - Minimum size equipment grounding conductors for grounding raceway and equipment Table 2 – Minimum size equipment grounding conductors for grounding raceway and equipment Aluminum Cable Tray Systems Table 392.60(A) – Metal area requiremen
GENERAL MARKING ADVICE: Accounting Higher Solutions. The marking schemes are written to assist in determining the “minimal acceptable answer” rather than listing every possible correct and incorrect answer. The following notes are offered to support Markers in making judgements on candidates’ evidence, and apply to marking both end of unit assessments and course assessments. Page 3 .
