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The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Codes series published by the National Fire Protection Association (NFPA), a private trade association.[1] Despite the use of the term “national”, it is not a federal law. It is typically adopted by states and municipalities in an effort to standardize their enforcement of safe electrical practices.[2] In some cases, the NEC is amended, altered and may even be rejected in lieu of regional regulations as voted on by local governing bodies.

The “authority having jurisdiction” inspects for compliance with these minimum standards.[3][4]

NEC

The National Electrical Code, 2008 edition

Background[edit]

The NEC is developed by NFPA’s Committee on the National Electrical Code, which consists of 19 (20 in 2008) code-making panels and a technical correlating committee. Work on the NEC is sponsored by the National Fire Protection Association. The NEC is approved as an American national standard by the American National Standards Institute (ANSI). It is formally identified as ANSI/NFPA 70.

First published in 1897, the NEC is updated and published every three years with the 2014 edition being the most current. Most states adopt the most recent edition within a couple of years of its publication. As with any “uniform” code, a few jurisdictions regularly omit or modify some sections, or add their own requirements (sometimes based upon earlier versions of the NEC, or locally accepted practices). However, the NEC is the least amended model code, even with it setting minimum standards. No court has faulted anyone for using the latest version of the NEC, even when the local code was not updated.[5]

In the U.S., anyone, including the city issuing building permits, may face a civil liability lawsuit for negligently creating a situation that results in loss of life or property. Those who fail to adhere to well known best practices for safety have been held negligent. This liability and the desire to protect residents has motivated cities to adopt and enforce building codes that specify standards and practices for electrical systems (as well as other departments such as water and fuel-gas systems). This creates a system whereby a city can best avoid lawsuits by adopting a single, standard set of building code laws. This has led to the NEC becoming the de facto standard set of electrical requirements.[6] A licensed electrician will have spent years of apprenticeship studying and practicing the NEC requirements prior to obtaining his or her license.

The Deactivation and Decommissioning (D&D) customized extension of the electrical code standard defined by National Electrical Code was developed since current engineering standards and code requirements do not adequately address the unique situations arising during D&D activities at U.S. Department of Energy (DOE) facilities. The additional guidance is needed to clarify the current electrical code for these situations. The guidance document provides guidance on how to interpret selected articles of NFPA 70, “National Electrical Code” (NEC), in particular certain articles within Article 590, “Temporary Power,” for D&D electrical activities at DOE sites.[7]

The NEC also contains information about the official definition of HAZLOC and the related standards given by the Occupational Safety and Health Administration and dealing with hazardous locations such as explosive atmospheres.

Public access[edit]

The NEC is available as a bound book containing approximately 1000 pages. It has been available in electronic form since the 1993 edition. Although the code is updated every three years, some jurisdictions do not immediately adopt the new edition.

The NEC is also available as a restricted, digitized coding model that can be read online but not saved, copied and pasted, or printed, free of charge on certain computing platforms that support the restricted viewer software.

In the United States, statutory law cannot be copyrighted and is freely accessible and copyable by anyone.[8] When a standards organization develops a new coding model and it is not yet accepted by any jurisdiction as law, it is still the private property of the standards organization and the reader may be restricted from downloading or printing the text for offline viewing. For that privilege, the coding model must still be purchased as either printed media or a CD-ROM. Once the coding model has been accepted as law, it loses copyright protection and may be freely obtained at no cost.

Archive.org and many state or local government sites allow download of the NEC without the registration that the NFPA requires.

External links to both the restricted NEC online access and free public access sites are referenced at the end of this article.

Structure[edit]

The NEC is composed of an introduction, nine chapters, annexes A through I, and the index. The introduction sets forth the purpose, scope, enforcement and rules or information that are general in nature. The first four chapters cover definitions and rules for installations (voltages, connections, markings, etc.), circuits and circuit protection, methods and materials for wiring (wiring devices, conductors, cables, etc.), and general-purpose equipment (cords, receptacles, switches, heaters, etc.). The next three chapters deal with special occupancies (high risk to multiple persons), special equipment (signs, machinery, etc.) and special conditions (emergency systems, alarms, etc.). Chapter 8 is specific to additional requirements for communications systems (telephone, radio/TV, etc.) and chapter 9 is composed of tables regarding conductor, cable and conduit properties, among other things. Annexes A-I relate to referenced standards, calculations, examples, additional tables for proper implementation of various code articles (for example, how many wires fit in a conduit) and a model adoption ordinance.

The introduction and the first 8 chapters contain numbered articles, parts, sections (or lists or tables) italicized exceptions, and Informational notes – explanations that are not part of the rules. Articles are coded with numerals and letters, as ###.###(A)(#)(a). For example 804.22(C)(3)(b) would be read as “section 804 point 22(C)(3)(b).” and would be found in chapter 8. For internal references, some lengthy articles are further broken into “parts” with Roman-numerals (parts I, II, III, etc.).

Each code article is numbered based on the chapter it is in. Those wiring methods acceptable by the NEC are found in chapter 3, thus all approved wiring method code articles are in the 300s. Efforts have been underway for some time to make the code easier to use. Some of those efforts include using the same extension in those code articles for the support of wiring methods.

The NFPA also publishes a 1,497-page NEC Handbook (for each new NEC edition) that contains the entire code, plus additional illustrations and explanations, and helpful cross-references within the code and to earlier versions of the code. The explanations are only for reference and are not enforceable.

Underwriters Laboratories, one of many of the recognized testing laboratories by the US Department of Labor.

Many NEC requirements refer to “listed” or “labeled” devices and appliances, and this means that the item has been designed, manufactured, tested or inspected, and marked in accordance with requirements of the listing agency. To be listed, the device must meet testing and other requirements set by a listing agency such as Underwriters Laboratories (UL), MET Laboratories, Inc. (MET), Intertek Group ( Formerly ETL), Canadian Standards Association(CSA), or FM Approvals (FM). These are examples of “national recognized testing laboratories” (NRTLs) approved by the United States Department of Labor, Occupational Safety and Health Administration (OSHA) under the requirements of 29CFR1910.7.[9] Only a listed device can carry the listing brand (or “mark”) of the listing agency. Upon payment of an investigation fee to determine suitability, an investigation is started. To be labeled as fit for a particular purpose (for example “wet locations”, “domestic range”) a device must be tested for that specific use by the listing agency and then the appropriate label applied to the device. A fee is paid to the listing agency for each item so labeled, that is, for each label. Most NRTLs will also require that the manufacturer’s facilities and processes be inspected as evidence that a product will be manufactured reliably and with the same qualities as the sample or samples submitted for evaluation. An NRTL may also conduct periodic sample testing of off-the-shelf products to confirm that safety design criteria are being upheld during production. Because of the reputation of these listing agencies, the “authority having jurisdiction” ( or “AHJ” – as they are commonly known) usually will quickly accept any device, appliance, or piece of equipment having such a label, provided that an end user or installer uses the product in accordance with manufacturer’s instructions and the limitations of the listing standard. However, an AHJ, under the National Electrical Code provisions, has the authority to deny approval for even listed and labeled products. Likewise, an AHJ may make a written approval of an installation or product that does not meet either NEC or listing requirements, although this is normally done only after an appropriate review of the specific conditions of a particular case or location.

The 2008 Code has user-friendly features to aid the reader in seeing changes. Revisions or additions to the articles from the 2005 version are highlighted in gray shading. Where sections have been deleted, a bullet (•) is shown between the paragraphs that remain.

High and low voltage rule classification[edit]

The electric code makes a distinction between “high” voltages (100 volts and higher), and “low” voltages below that, and which have two different safety classifications and regulations. For circuits defined as low voltage, in some jurisdictions, there no requirement for licensing, training, or certification of installers, and no inspection of completed work is required, for either residential or commercial work. Low voltage cabling run in the walls and ceilings of commercial buildings is also typically excluded from the requirements to be installed in protective conduit.

The precise reasoning for the selection of 100 volts as the division between high and low is not clearly defined, but appears to be based on the idea that a person could touch the wires carrying low voltage with dry bare hands, and not be electrocuted, injured, or killed. This is generally true for 12 volt systems, but becomes more ambiguous as the voltage increases to 100.

The meaning also varies when alternating current is used, as there is the more commonly known root mean square voltage (120v) but also a peak wave voltage (170v). Telephones for example use low voltage cabling, but the ringing voltage from the central office is approximately 90 volts peak AC, and which has an RMS voltage of 63v.

In more recent terms, the upper cutoff for what is considered low is approximately 50 volts, with most computer network equipment operating at 48 volts DC or lower, and not requiring special training to connect or use.

Although low voltage cabling does not require inspection or training to install in some jurisdictions, it is still important for installers to be aware of specific electric code safety rules such as how to correctly penetrate building fire barriers and use firestop putty (intumescents) to prevent a low voltage cable from reducing building fire protection and increasing the risk of injury or death for building occupants. Access to such safety information is typically restricted and limited access by the electrical industry itself so as to only permit licensed professionals to learn the NEC rules and educate themselves.[10]

Requirements[edit]

Article 210 addresses “branch circuits” (as opposed to service or feeder circuits) and receptacles and fixtures on branch circuits.[11] There are requirements for the minimum number of branches, and placement of receptacles, according to the location and purpose of the receptacle outlet. Ten important items in Article 210 have been summarized in a codebook.[12]

Feeder and branch circuit wiring systems are designed primarily for copper conductors. Aluminum wiring is listed by Underwriters Laboratories for interior wiring applications and became increasingly used around 1966 due to its lower cost. Prior to 1972, however, the aluminum wire used was manufactured to conform to the 1350 series aluminum alloy, but this alloy was eventually deemed unsuitable for branch circuits due to galvanic corrosion where the copper and aluminum touched, resulting in poor contact and resistance to current flow, connector overheating problems, and potential fire risk. Today, a new aluminum wire (AA-8000) has been approved for branch circuits that does not cause corrosion where it contacts copper, but it is not readily available and is not manufactured below size #8 AWG. Hence, copper wire is used almost exclusively in branch circuitry.

A ground fault circuit interrupter (GFCI) is required for all receptacles in wet locations defined in the Code. The NEC also has rules about how many circuits and receptacles should be placed in a given residential dwelling, and how far apart they can be in a given type of room, based upon the typical cord length of small appliances.

Polarized, grounding, 120-volt receptacle

As of 1962 the NEC required that new 120-volt household receptacle outlets, for general purpose use, be both grounded and polarized. NEMA connectors implement these requirements.

The NEC also permits grounding-type receptacles in non-grounded wiring protected by a GFCI.

240 V receptacle faces

The 1999 Code required that new 240-volt receptacles be grounded also, which necessitates a fourth slot in their faces. These standards changes often cause problems for electrical work in older buildings.

A 120-volt combination AFCI/GFCI receptacle

Unlike circuit breakers and fuses, which only open the circuit when the current exceeds a fixed value for a fixed time, a GFCI device will interrupt electrical service when more than 4 to 6 milliamperes of