Professional and Skillful Installations
Good workmanship is essential to the performance of a system or installation. The safety of a system or installation depends on the quality of the workmanship by a qualified person. Installation of an equipment grounding conductor (EGC) is a good example of how required workmanship directly relates to performance. Poor workmanship can affect the integrity and performance of EGCs, resulting in loose connections, unsupported wiring methods, improper sizing, incorrect selection of overcurrent protective devices and more.
1. An EGC, as defined in the National Electrical Code, performs which of the following functions?
The Article 100 definition of the term Grounding Conductor, Equipment (EGC) and informational note provide information about the functional aspects of equipment grounding conductors of all types and forms.
2. Which of the following is not recognized by the NEC as an acceptable EGC?
Section 250.118(9) currently only recognizes the copper sheath of mineral-insulated, metal-sheathed cable, not MI cable with a stainless steel sheath.
3. All electrical equipment shall be installed in a professional and skillful manner.
Section 110.12. This section addresses the mechanical execution of work. The Informational Note following this rule references industry standards are available that clearly address what constitutes good workmanship and acceptable industry practices.
4. Where required to comply with 250.4(A)(5) or 250.4(B)(4), wire-type EGCs shall be larger than the sizes specified in Table 250.122.
The note at the bottom of Table 250.122 is a code rule and not an Informational Note. It references Sections 250.4(A)(5) and 250.4(B)(4) and is enforceable.
5. What is the minimum size copper-clad aluminum EGC required for a 1,000A feeder installed in rigid nonmetallic conduit?
Section 250.122 and Table 250.122 using the aluminum or copper-clad aluminum column in the table. The question seeks the minimum size, but answer c. would certainly be acceptable as an EGC for this circuit.
6. Good workmanship requires EGCs consisting of raceways, cable trays, cable armor, cablebus framework or cable sheaths or wires within raceways or cables and shall be installed with all connections, joints and fittings made tight.
Section 250.120(A) provides this general requirement that is directly related to good workmanship. Specific tightening torque values are often required as marked on equipment.
7. As defined currently, which of the following is not a characteristic required for a qualified person?
The Article 100 definition of the term “Qualified Person” currently does not require training and experience, but those are essential factors in consideration of one being qualified.
8. Industry standards are available that provide information about good workmanship in electrical construction and accepted industry practices to accomplish it.
Section 110.12 and Informational Note No. 1 references workmanship standards
9. The NEC generally requires conductor overcurrent protection and provides information about obtaining wire-type conductor short-circuit withstand ratings.
Section 240.4 and Informational Note that refers to the Insulated Cable Engineers Association (ICEA) publication Short Circuit Characteristics of Insulated Cables.
10. Because of concerns of EMT being an effective ground-fault current path to comply with Section 250.4(A)(5), the NEC limits the length of electrical metallic tubing to which of the following lengths?
The NEC does not limit the length of EMT as an acceptable equipment grounding conductor. This is a design consideration. When excessive lengths are installed, consideration should be given to installing a supplemental, wire-type equipment grounding conductor with the contained circuit conductors. The Steel Tube Institute provides information about significant testing of conduit and tubing to determine performance as an effective ground-fault current path. Testing was performed by the Georgia Institute of Technology and resulted in software (GEMI) available to assist with these design considerations.
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