Dissecting NEC’s recent changes

Changes in and additions to the 2017 edition of NFPA 70: National Electrical Code (NEC) have an impact on commercial and industrial facilities.

12/18/2017


This article has been peer-reviewed.Learning objectives:

  • Understand the basics of NFPA 70: National Electrical Code (NEC).
  • Know that NEC is updated every 3 years, and understand the changes to the 2017 edition.
  • New articles were introduced recently; learn about them here.

Do engineers need to know NFPA 70: National Electrical Code (NEC)? Certainly! NFPA 70 is adopted into law in every state in the country, as well as in many foreign countries.

In Article 90.1, the first paragraph of the NEC, it is clearly stated that it is not a design document. However, it is the basis of every electrical design and is the minimum standard that will provide a safe and legally acceptable design. While the NEC may allow an engineered system that goes beyond the requirements of the code to provide more efficiency and convenience, it does not require efficiency or convenience.

The NEC assumes the user has some training in and at least a basic understanding of electrical principles. This typically is not a concern for electrical engineers, but it may present a challenge for those expanding into areas of design and construction in which they are not familiar.

The NEC is a consensus document with changes proposed, evaluated, and reviewed by numerous members along with additional public input for each change that appears in the document. Every 3 years, the NEC introduces new safety concepts. Sometimes, it even forces the industry to bring new products to market that are in development but proceeding more slowly than the NFPA consensus feels is reasonable. These new products will cause development of new procedures for installation and new requirements for design.

Figure 1: Facing switchgear is shown with an aisle in between. Because the working space for 4,160 V gear is not in accordance with current requirements, this gear is being demolished. All graphics courtesy: JacobsNew NEC articles

The 2017 edition of the NEC has introduced five new articles. These include some interesting and sometimes confusing requirements that affect electrical design. The new articles are briefly discussed below:

Article 425—Fixed Resistance and Electrode Industrial Process Heating Equipment: Previous versions of the NEC included requirements for space heating, pipeline heating, and deicing/snow melting, but did not address electric boilers or other process heating. This new article fills this void. Now there are requirements that provide the minimum for a safe installation.

Article 691—Large-Scale Photovoltaic (PV) Electric Power Production Facility: Large PV systems have unique safety and operational features because the power source (the sun) is not controllable. This new article addresses these complications in large PV arrays not controlled by a utility.

Article 706—Energy Storage Systems: With the proliferation of nonutility energy-production facilities, there also has been an increase in energy storage to supplement the production, so the time of energy use can be coordinated with the cost of power. This new article addresses the safety concerns for having a large number of storage batteries in close proximity.

Article 710—Stand Alone Systems: Most places in the U.S. now have access to utility-provided electricity, but not everywhere. Where utility power is not available, or where someone chooses not to connect to the utility, the electric installation now has criteria directed specifically to it.

Article 712—Direct Current Microgrids: Dc microgrids connect dc power supplies and loads. The sources may be solar systems, wind power systems, fuel cells, or batteries. Many types of loads now have dc versions, including lighting and motors. Because of the limited effective transmission distance of dc power, these microgrids are limited to small areas.

Figure 2: Access to electrical equipment is an NEC requirement, but this access is hard to maintain in many industrial facilities.Changes to existing articles

Along with the new articles, there were more than 4,000 public inputs (requests for changes) and more than 500 changes to existing requirements. Some of these changes include:

A change to the definition of “readily accessible” clarifies that it is permissible to lock electrical equipment or electrical rooms to limit access by unauthorized personnel (Article 100).

Article 110.16(B): Service equipment rated 1,200 amp and larger must be marked with arc flash data. The data required will require arc flash calculations, and it should be clear in the contract who must provide this data. Some owners want to see the data prior to the end of design so changes to the design can be made to lessen the arc flash. Calculations not based on the actual equipment installed and actual conductor types and lengths are always an approximation. But waiting for the contractor to install equipment and conductors that do not meet arc flash requirements can result in large change orders. Arc flash labels can be factory- or field-applied. The label contents are defined along with the new Article (110.16(B)). Because arc flash is a huge safety concern, the 2017 edition continues the effort to minimize arc flashes with requirements and methods for reducing the energy that flows through fuses and circuit breakers rated at 1,200 amp or higher.

Continued expansion of ground-fault circuit interrupter (GFCI) protection includes single-phase receptacles up to 50 amp and 3-phase receptacles up to 100 amp. This expanded protection is required for nonresidential installations nits where voltage doesn’t exceed 150 V to ground and in locations listed in 210.8(B). GFCI is also required for lighting outlets in crawl spaces, the reason being there is little possibility of falling away from an electrical fault while in a crawl space. Also, any person in a crawl space is most likely well-grounded.

The locations requiring arc fault and tamper-resistant receptacles also have expanded. Arc fault receptacles have the ability to reduce fires that result from arcing at conductor connections. The locations where they are required have been slowly increasing since their inclusion in the code. Tamper-resistant receptacles protect people, particularly children, from electric shock and arcing flash burns by reducing the possibility of inserting metal objects into a receptacle. Locations where they are required, usually where children might not be closely supervised, have been increasing each code cycle.

The number of receptacles in meeting rooms must meet minimum requirements based on the size of the room. The receptacles can be located to suit the designer. Also, rooms between 225 and 760 sq ft must have floor receptacles located at least 6 ft from any wall.

When conduits are run across a rooftop, previous editions of the NEC had a table listing derating factors based on their height above the roof. The reason for this was a study showing that the conductors in the conduits were exposed to higher temperatures because of the heat radiating from the roof. More recent studies have shown the initial study was flawed and the conductors are not subjected to an appreciable temperature gradient. The 2017 edition has removed the table and the requirement for derating, except if the conduit is less than 7/8 in. above the roof.

Many types of power distribution and control equipment must now be marked with the short-circuit rating, and documentation must be available to inspecting authorities showing the available short-circuit current at the installation location. Making sure all equipment is capable of withstanding available short-circuit current provides a measure of personnel protection and prevents extreme damage to equipment. Having the documentation, calculations, and equipment submittals on hand may require much more extensive calculations than previously. This may require more expensive versions of the calculation programs.

Figure 3: Part of a large solar application is shown. Facilities 5 MW and larger must comply with NEC-2017’s new Article 691.NEC chapters

The NEC is divided into nine chapters; chapter nine is tables. Each has different functions and addresses different aspects of electrical installation.

Chapter 1—General is the basis for the application of the code. Terms that are used by more than one article are defined in Article 100; terms that are in common use and not given special meanings within the electrical trade are not defined. Also included in Chapter 1—in Article 110, Requirements for Electrical Installations—are requirements for listing and marking, working space, and guarding of live parts. A strong working knowledge of this chapter is fundamental to understanding the code.

Chapter 2—Wiring and Protection contains the requirements for branch circuits including identification, protection of conductors, GFCI protection, arc fault protection, and bonding and grounding. Proper grounding and bonding is one of the most important items in the code for the protection of wiring, equipment, and most important, people. Nothing else does as much to channel voltage from faults away from people and equipment and provide stable power for the operation of equipment, particularly electronics. It is interesting that surge arrestors and surge protective devices are included in Chapter 1 and not Chapter 6—Special Equipment. The reliance on proper grounding for these devices to perform their function is a big consideration in this location.


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