Transcription
Grounding of ElectricalSystemsNEW CODE: Grounding andBondingPresented ByScott Peele PE
Grounding of ElectricalSystems OutlinezzzzzzzzzDefining the TermsWhy should I Ground?Types of Grounding SystemsSeparately Derive SystemGrounding ElectrodeBondingGround Fault ProtectionGround Reference or Signal ReferenceGrounding for Lightning Protection
DefinitionszzzzzzReview definition as we encounter them.Grounded vs GroundingIsolated GroundFloating GroundGround LoopNet Current
Why am I grounding or Not?zzzzzzSafetyGrounding for Fault Current PathsGrounding for Touch Potential (static)Grounding for Lightning Protection SurgeArresters, TVSS (SPD)Grounding for Signal Reference (RF, Data,static ,etc.)Not Grounding Continuous operation
Three reasons for eference
Grounded vs GroundingzzGrounded vs. grounding in an electricalsystem. Grounded system refers to asystem where a conductor is groundedand is intended to or may carry current inthe normal operation. The neutral on awye system is a prime example of agrounded conductor.The grounding conductor system is notintended to carry operational current in itsdesign. This path is intended to carryunwanted and fault currents for protection.
Types of AC Grounded SystemszzzzzUngrounded systemSolidly Grounded SystemResistance GroundedReactance GroundedGround Fault Neutralizer
Which System to Use?zzzzzzzSafety - Who is Operating the SystemGround Fault DetectionSignal ReferenceTouch Potential (also static)Available Fault Currents?Operation StabilitySystem Response
Ungrounded SystemzzzType of system typically used on is aDelta service.Some time used on a floating WyeDetection System in Place Ground Detection by LightingZigzag Grounding TransformerGround RelayGround Fault ?
Detection Devices
Solidly Grounded SystemzzzzzUsually use in Wye systemsReturn Fault current to trip overcurrentprotection device quicklyUsually better reference and safer systemMuch better for lightning protectionCan be used in Corner Grounded Delta Problems with phase grounded re-groundedNot good on lightning protection equipment
Resistive groundedzLow Resistance zLimit Fault CurrentMinimizes the damage at the faultUsed usually with multiple sources i.e.transformers, and or generatorsHigh Resistance Enables system operation with one phasegroundedEnables current to flow for detection networksCurrent is low enough so that no damage occurs
Reactance GroundingzReactor connected between systemneutral and ground Reduces the ground fault current betweenphase and groundUsually higher fault current than lowresistance groundingBetter coordination with fault currents onmulti-grounded system. Mostly used onsystem above 5kV.
Ground-Fault NeutalizerzzzReactor with relatively high value ofreactance.Usually on system above 15kV phase toground air exposed. (overheadTransmission and Distribution)May provide insulator flashover with selfextinguishing characteristics.
Separately Derived SystemzzzThe system grounding conductor for aseparately derived system shall begrounded at only one point.Main system Disconnecting means for amain utility feed, or a step down or step uptransformer, or a generator could all beseparately derived systems.When grounded it will be grounded at thenearest grounding electrode.
Grounding Electrode System andGrounding Electrode Conductor Part IIIzNEC 250.50 (Grounding Electrode System) 250.52 Electrodes Water Pipe if 10 ft. or more of metal water pipe is in contactwith the earth. Metal Frame of the Building or Structure where the followingmethods are used to make an earth connection: (1,2,3,4) Concrete-Encased Electrode in at least 2” of concretelocated within and near the bottom of a concrete foundationor footing that is in indirect contact with the earth. Ground Ring encircling the building or structure in directcontact with the earth Rod or Pipe electrode not less than 8 ft in length Plate Electrode not less than 2 square ft. Other Local underground systems such as piping,underground tanks and underground metal well casing NOT PermittedMetal underground gas piping Aluminum electrode
Grounding Electrode SystemzInstallation NEC 250.53 zThis requirement clarifies that thesupplemental electrode system must beinstalled as if it were the sole groundingelectrodeBonding NEC 250.53 C This requirement is for bonding ofmultiple electrodes.
BondingzBonding for Main Bonding JumperSystem Bonding JumperElectrode BondingPart V Bonding Wherenecessary to ensure electrical continuityand the capacity to conduct safely and faultcurrent likely imposed.
Ground ?HotNeutralGround
Review Ohms LawVoltage Current X evelop VOLTAGEDevelop VOLTAGECurrent Source LightningAverage current 30,000 ampsGroundRod
Grounding and BondingVoltage DifferenceTransient voltages andcurrents at data port orcable connections
Isolated GroundzzzzNEC 250.146 (D) Isolated groundreceptacle (orange triangle) NEC 406.2(D)NEC 250.96 (B) Isolated GroundingCircuitsNEC 647 Section Sensitive ElectronicEquipment.NEC 647.6 Grounding. “Technical Equipment Ground”
Isolated GroundIsolated grounded receptacle has an isolated terminal from the yoke to the groundLug. These receptacle are usually marked with an orange triangle or all orange.Sub PanelNeutral BusGround Bus
Floating GroundzzzzThe neutral on a wye system is notintentionally groundedSignal conductor shielding is notintentionally groundedProblem is high transient voltage orovervoltages may exist causing damage.Not a good way for lightning protection
Ground LoopzzzzGrounds from two different derived systemare connectedOpen ground loops. Grounds are notbonded properly and cause damage.Ground loops cause circulating currentbetween systems and cause transformercoupling (CT’s)Signal reference can be compromisedcausing data errors.
Grounding for Signal ReferencezzzzzzDon’t Burst the Bubble.Ground on one endGround on both endsGround on neither endFiber Optic Best AnswerOptical Coupler
Don’t Burst the Bubble
Ground Fault Interrupter Function
Net CurrentzCurrents that are not apart of the normaloperation of a derive electrical system. All positive, negative, and zero sequencecurrents added and the resultant currentare net currents.
Books On GroundingzNECzIEEE zGreen Book 142-1991“Recommended Practice forGrounding of Industrial and Commercial PowerSystems”Emerald Book 1100-1999 “RecommendedPractice for Powering and Grounding SensitiveElectronic Equipment”Industrial and Commercial Power systemHandbook
Grounding Electrode System and Grounding Electrode Conductor Part III zNEC 250.50 (Grounding Electrode System) 250.52 Electrodes Water Pipe if 10 ft. or more of metal water pipe is in contact with the earth. Metal Frame of the Building or Structure where the followin
