MEA 2017 NEC Grounding And Bonding Part 1

ce) so high current are interrupted inless time6030

11/13/2018Art 100 Ground-Fault Current Path Def. Ground-Fault Current Path. An electricallyconductive path from the point of a ground fault on awiring system through normally non–currentcarrying conductors, equipment, or the earth, - to theelectrical supply source. “Facilitates the operation of the overcurrentdevice or ground fault detectors on a highimpedance grounded systems.”61Copyright Cengage Learning31

11/13/2018Effective Ground-Fault Current PathIntentionally constructed Deliberate steps taken to create the path Properly connect all components Carries fault-current to facilitate operationof overcurrent device or ground-faultdetector 63Effective Ground-Fault Current PathLow-impedance “Impedance” is totalopposition to currentflow in ac circuits All circuit conductorsmust be installed inclose proximity toreduce impedance See 300.3(B) –(conductors of thesame circuit) Copyright Cengage LearningAdds to impedance6432

11/13/2018Effective Ground-Fault Current PathAll circuitconductors must beinstalled in closeproximity somagnetic lines offorce can cancelThis helps ensure alow-impedancefault-current path Amps ofallAmps ofoneAll currents measuredtogether- should be zeroCopyright Cengage Learning65Rating and Operation of OvercurrentDevices Tested to carry full load current indefinitelyNEC requires circuit to be no more than 80percent of rated current unless overcurrentdevice is rated for 100 percent operationTime-current curves should be consulted todetermine the amount of current required toreach the instantaneous trip modeImpedance of fault current path must be lowenough to facilitate operation of OCP6633

11/13/2018Time current curves67Effective Ground-Fault Current Path Continuous and reliableComponents and connections are intended tolast for the life of the installationUnless monitored, equipment grounding pathcan be incomplete without indication (loosefittings)Does not carry current in normaloperationOften, a break in the Path is discovered byelectric shock after faulted equipmentbecomes energized6834

11/13/2018Path Through the EarthThe path through the earth can be in parallel withground-fault current return path where more thanone connection to earth exists. The earth is not considered an “effectiveground-fault current path”. Connections are made to earth for otherpurposes, but never to carry fault current. Path only through the earth will result in electricalequipment presenting a dangerous electric shockhazard. 69Copyright Cengage Learning7035

11/13/2018Parallel Conductors 310.10 (H)Parallel conductor installations to be made underrules in 310.10(H) Two or more conductors are connectedtogether at each end to create a conductive pathwith increased capacity. Concept is to have all conductors share currentequally Equipment grounding conductors are installed inparallel under rules of 250.122(F) New parts1-2 71250.122 (F) Conductors in parallel (F)(1)(a) If conductors are installed inparallel in the same raceway or cable tray, asingle wire type conductor shall bepermitted as the equipment ground. - basedon 250.122 and overcurrent protection(b) If wire type conductors are installed inmultiple raceways, wire type groundingconductors where used shall be installed inparallel in each raceway based on 250.122and the overcurrent protection36

11/13/2018250.122 (F) Conductors in parallel(F)(2)(a) If multi-conductor cables areinstalled in parallel the groundingconductors in each cable shall beconnected in parallel (b) If multi-conductor cables are installedin parallel in the same raceway, a singlewire-type grounding conductor with thecable grounding wires shall be permittedto be connected together Copyright Cengage Learning7437

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11/13/2018 2 Objectives Using accepted definitions of terms applicable to grounding & bonding Provide a low-impedance path of proper capacity to ensure the operation of overcurrent protective devices Various components of the grounding & bonding system Electric shock hazards & effect of electricity