From the time the project is being designed until the final receptacle is installed, the requirements in the National Electrical Code apply. Just like every building and structure must be built on a solid foundation with structural integrity to support all loads, every electrical system supplying a structure must be installed with the grounding electrode system serving as its foundation.
Since a building’s footing or foundation is part of the grounding electrode system, the concrete-encased electrode is one of the first installed. Other grounding electrodes, such as metal water pipe and metal in-ground support structures, are often inherent to buildings. These electrodes are formed or installed as construction progresses.
NEC structure overview
The NEC is an installation code containing requirements that apply to electrical wiring and equipment. It consists of an introduction and nine chapters. Each one contains articles that are further broken down into rules in the form of parts, sections, subdivisions and lists. Also included are exceptions to rules, informational notes and rules in tabular form.
Article 90 is the introduction and provides users with essential information about the NEC structure and how the rules apply to electrical installations. Section 90.2(A) indicates that its purpose is the practical safeguarding of persons and property against hazards arising from the use of electricity. This provision also indicates that the NEC is not intended as a design specification or manual for untrained people. Section 90.2(C) provides what the rules do and do not cover. Section 90.3 is an important provision that guides users in the correct application of the stated rules.
Chapters 1 through 4 have general application, meaning they apply to all electrical installations. Chapters 5, 6 and 7 include rules for special occupancies, special equipment and other special conditions. The provisions in chapters 5, 6 and 7 modify or amend the requirements in chapters 1 through 7, as there are requirements in chapters 5, 6 and 7 that modify requirements in other articles within those three chapters.
Chapter 8 is not subject to the general requirements of the other chapters except where the other rules are referenced from that chapter. Chapter 9 includes tables used in applying the other Code requirements. The annexes in the back of the NEC contain information that is not mandatory but often valuable in helping users understand how various requirements apply to installations and systems.
There are many grounding and bonding requirements in Chapter 5 that are often more restrictive than the general rules in Article 250. For example, 250.118(6) recognizes listed liquidtight flexible metal conduit (LFMC) as an acceptable equipment grounding conductor (EGC) if all the conditions indicated in 250.118(6)(a) through (e) are met. This means that listed LFMC can be installed and used as an EGC without installing a wire-type EGC with the short run of listed LFMC.
Chapter 5 includes requirements for special occupancies and often modifies the general requirements of the Code to be more restrictive. For example, Article 501 covers installations in Class I locations where explosion hazards exist, and 501.30(B) specifically restricts LFMC and flexible metal conduit from being used as the sole bonding means.
As such, there is a requirement to install a wire-type equipment bonding jumper in accordance with 250.102. The bonding jumper can be inside or outside the conduit to ensure that an LFMC is not depended on for carrying ground-fault current in a Class I hazardous location. The conduit and equipment bonding jumper are used, meaning the LFMC does not function as the sole effective path for ground-fault current during ground-fault conditions. This could become an ignition source in an explosive atmosphere where fumes or vapors such as gasoline are present.
Special consideration is necessary for grounding and bonding of exposed noncurrent-carrying metal equipment parts, such as metal exteriors of motors, luminaires and fixed or portable lamps. These parts must have effective mechanical and electrical connections to reduce the possibility of arcs or sparks during ground faults caused by ineffective or poor grounding and bonding methods.
About The Author
JOHNSTON is NECA’s executive director of codes and standards. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at [email protected].