What is the relationship between NFPA 70 (the National Electrical Code), NFPA 70B (Maintenance for Electrical Equipment), and NFPA 70E (Safety Related Work Practices)? An Electrical Contractor reader asked if I would explain how NFPA 70, 70B and 70E were related in codes and standards application. I’ll honor his request by starting with the NEC and explaining how each of these documents are used and how they interface. In the next couple of months, this column will discuss 70B and 70E.

The NEC is mainly used as an installation code for electricians when installing wiring methods and electrical equipment in residential units and commercial and industrial facilities. The NEC is divided into nine chapters that contain articles with sections that address requirements pertaining to specific Code rules.

Chapter 1 contains Articles 100 and 110, which defines key words for more easily understanding a particular Code rule. Consider the word “ground.” In Code application, it simply means “earth.” And when used in a grounding paragraph, it means earth-grounded. For a better understanding of how to interpret the requirements of the NEC, electricians should review the definitions in Article 100 that relate to their job tasks.

Chapter 2 (Articles 200 through 285) is considered the design and protection chapter. Electricians use it to calculate loads for selecting the elements of services, feeders and branch-circuits. For example, if an electrician is given the responsibility to calculate the load of a branch circuit to determine the ampacity for sizing the overcurrent-protection device and branch circuit conductors, 210.19(A)(1) and 210.20 can be used. However, if the requirements are not available in Chapter 2 to calculate a particular load, Chapter 2 will refer the user to the appropriate article and section that address the requirements pertaining to his or her calculation. For instance, 220.14(C) and 220.50 refers to 430.22 to obtain the guidelines for figuring the individual load for a motor.

Chapter 3 (Articles 300 through 398) addresses wiring methods and items from which an installation is built, such as conductors. It also recognizes equipment and wiring methods needed to complete the installation. By referencing Part II of Article 344 and scrolling the various sections, the support requirements for rigid metal conduit (RMC) can be located. Therefore, an electrician can locate the rules by reading maybe a page and a half. Section 344.30(A) and (B) requires a run of RMC to be securely supported at a minimum of 10 foot intervals and within 3 feet of pull boxes and junction boxes.

Chapter 4 covers equipment for general use. The first part mostly deals with electrical energy to perform work and is considered current-carrying equipment. In general, the latter part makes use of the effects of electricity to supply or control electricity, and such equipment is not always current-carrying. As indicated in Article 450, transformers can be located and installed per 450.9, 450.13 and 450.21. Protection in primary or primary and secondary can be determined by applying the percentages in Tables 450.3(A) and (B). These sections help an electrician get started in installing and protecting transformers that are located in commercial and industrial facilities.

Chapter 5 was written to protect personnel and equipment from the electrical hazards that might occur in a particular occupancy. Sections 500.2 and 500.7 are used to selected equipment located in hazardous (classified) areas to reduce the threat of explosions and the protection of people and property. Other articles in Chapter 5 are designed to do the same.

Chapter 6 discusses special equipment and provides specific requirements for equipment not in Chapters 4 and 5. Under certain conditions, 670.1, Fine Print Notes 1 and 2 do not require, when installing industrial equipment, the strict clearances for workspace as required by 110.26 for equipment in Chapters 4 and 5.

Wiring methods and equipment located in Chapter 7 are basically used for signaling, control, fire alarm circuitry or backup power through transfer switches, should the normal power fail.

Chapter 8 is loaded with requirements for communications and other transmitting- and receiving-related equipment.

Finally, the first tables in Chapter 9 (the last chapter) are devoted to sizing nipples, sleeves, conduits and tubing based on the number of enclosed conductors. When these tables are used, the notes in Chapter 9 should be reviewed.

Correction: In “A Tragic Installation” (EC, September 2009, pg. 130), under “Site inspection,” the word “recommended” should have been “required.” In the second paragraph, “equipment-grounding conductor” should be replaced with “effective ground-fault current path.” Under “No job briefing performed,” “equipment-grounding conductor” should be “effective ground-fault current path.”

Rationale: Where the service is supplied by a utility system that is grounded, the grounded conductor (often a neutral) is required to be brought to the service-equipment enclosure and bonded to the service-equipment enclosure whether it serves a load or not [See 250.24(C)]. The reason is during ground-fault conditions, it serves as the effective ground-fault current path back to the utility source to facilitate operation of overcurrent devices. This is the point being made in this article.

STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.