The
National Electrical Code (
NEC), or
NFPA 70, is a regionally adoptable standard for the safe installation of
electrical wiringElectrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to...
and equipment. The NEC, while having no legally binding regulation as written, can be and often is adopted by states, municipalities and cities in an effort to standardize their enforcement of safe electrical practices within their respective jurisdiction. In some cases, the NEC is amended, altered and may even be rejected in lieu of regional regulations as voted on by the governing bodies of any given locale.
The NEC codifies the requirements for safe electrical installations into a single, standardized source. It is part of the National Fire Codes series published by the
National Fire Protection AssociationThe National Fire Protection Association is a United States trade association that creates and maintains private, copywrited, standards and codes for usage and adoption by local governments...
(NFPA), and while not itself a
U.S. lawThe law of the United States consists of many levels of codified and uncodified forms of law, of which the most important is the United States Constitution, the foundation of the federal government of the United States...
, NEC use is commonly mandated by
stateA U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
or
localA municipality is essentially an urban administrative division having corporate status and usually powers of self-government. It can also be used to mean the governing body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district...
law.
The "authority having jurisdiction" inspects for compliance with these minimum standards.
("National Electrical Code" and "NEC" are registered trademarks of the NFPA).
General
The NEC is developed by NFPA's Committee on the National Electrical Code, which consists of 19 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 InstituteThe American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...
(ANSI). It is formally identified as ANSI/NFPA 70.
First published in 1897, the NEC is updated and published every three years. The 2011 NEC is the current edition (effective date August 25, 2010). 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.
In the U.S., anyone, including the city issuing building permits, may face a civil
liabilityLegal liability is the legal bound obligation to pay debts.* In law a person is said to be legally liable when they are financially and legally responsible for something. Legal liability concerns both civil law and criminal law. See Strict liability. Under English law, with the passing of the Theft...
lawsuitA lawsuit or "suit in law" is a civil action brought in a court of law in which a plaintiff, a party who claims to have incurred loss as a result of a defendant's actions, demands a legal or equitable remedy. The defendant is required to respond to the plaintiff's complaint...
(be sued) 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 means that the city should adopt and enforce
building codeA building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the...
s 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 factoDe facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...
standard set of electrical requirements. A licensed
electricianAn electrician is a tradesman specializing in electrical wiring of buildings, stationary machines and related equipment. Electricians may be employed in the installation of new electrical components or the maintenance and repair of existing electrical infrastructure. Electricians may also...
will have spent years of
apprenticeshipApprenticeship is a system of training a new generation of practitioners of a skill. Apprentices or protégés build their careers from apprenticeships...
studying and practicing the NEC requirements prior to obtaining his or her license.
Public access to the NEC
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 free of charge on certain computing platforms. An external link to this online access is referenced at the end of this article.
In the United States, statutory law cannot be copyrighted and is freely accessible and copyable by anyone. 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.
Structure of the NEC
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.
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 has to meet the testing and other requirements set by a listing agency such as
Underwriters LaboratoriesUnderwriters Laboratories Inc. is an independent product safety certification organization. Established in 1894, the company has its headquarters in Northbrook, Illinois. UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing...
(UL),
MET Laboratories, Inc.MET Laboratories, Inc is an independent electrical testing and certification lab, recognized by the Occupational Safety and Health Administration...
(MET),
Intertek GroupIntertek Group plc is a global inspection, product testing and certification company headquartered in London, United Kingdom. It is the largest tester of consumer goods in the world and has a network of more than 1,000 laboratories in over 100 countries....
(ETL),
Canadian Standards AssociationThe Canadian Standards Association, also known as the CSA, is a not-for-profit Standards organization with the stated aim of developing standards for use in 57 different areas of specialisation...
(CSA), and 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. 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 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.
Details of selected NEC requirements
Articles 210 addresses "branch circuits" (as opposed to service or feeder circuits) and receptacles and fixtures on branch circuits. There are requirements for the minimum number of branches, and placement of receptacles, according to the location and purpose of the receptacle outlet. A
ground fault circuit interrupterA Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
(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.
As of 1962 the NEC required that new 120-volt household receptacle outlets, for general purpose use, be both
groundedIn electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
and
polarized.
NEMAis the association of electrical and medical imaging equipment manufacturers. Founded in 1926 and headquartered near Washington, D.C., its approximately manufacture products used in the generation, transmission, distribution, control, and end use of electricity. These products are used in utility,...
connectors implement these requirements.
The NEC also permits grounding-type receptacles in nongrounded wiring protected by a GFCI.
The 1999 Code required that new 240-volt receptacles be grounded also, which necessitates a fourth slot in their faces. These changes in standards often cause problems for people living in older buildings.
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 current in either conductor leaks to ground. A GFCI detects an imbalance between the current in the "hot" side and the current in the "neutral" side. One GFCI receptacle can serve as protection for several downstream conventional receptacles. GFCI devices come in many configurations including circuit-breakers, portable devices and receptacles.
Another safety device introduced with the 1999 code is the
arc-fault circuit interrupterAn Arc Fault Circuit Interrupter is a circuit breaker designed to prevent fires by detecting a non-working electrical arc and disconnecting the power before the arc starts a fire...
(AFCI). This device detects arcs from hot to neutral that can develop when insulation between wires becomes frayed or damaged. While arcs from hot to neutral would not trip a GFCI device since current is still balanced, circuitry in an AFCI device detects those arcs and will shut down a circuit. AFCI devices generally replace the circuit breaker in the circuit. They are required in new construction on all 15A and 20A 125V circuits to bedrooms, where most arc fault fires originate.
Conduit and cable protection
In home construction, wiring is commonly allowed to be installed directly in walls without additional protection. However, in commercial and industrial buildings, wiring needs to be protected from damage, so it is more commonly installed inside
conduitAn electrical conduit is an electrical piping system used for protection and routing of electrical wiring. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Flexible conduit is available for special purposes....
or ductwork made of metal, plastic, or passageways cast in concrete.
While some types of cable are protected by flexible spiraled metal armor, it is more common for conduit and ductwork to be installed empty and the wire pulled in later. The NEC spends considerable time documenting safe methods of installing cable in conduit, the primary concerns being the abrading of insulation, damage to the wire or insulation caused by sharp bends, kinking, and damage due to excess pulling strain.
A wire pulled with excessive force may break inside the conduit, requiring costly removal and replacement. However, a wire pulled with enough force to stretch the wire, but not break it, creates a hazard of future failure or fire. The stretched wire section will have a thinner cross section and higher resistance than other parts of the cable, and may have damaged insulation. Breaks may form in the stretched insulation, which may not be discovered until the circuit is powered and damage from arcing or shorting has occurred.
Wires must be protected from sharp metal edges of cut conduits or cabinet holes. The NEC specifies measures to protect wire insulation from damage by these edges during installation and use. For example, insulated cables may not be inserted directly through knockouts, due to the sharp edge around nearly all knockout holes. Clamping and other wire protection is often not required for plastic conduit parts, as plastic is not likely to damage insulation in contact with it.
In
hazardous locationsIn electrical engineering, a hazardous location is defined as a place where concentrations of flammable gases, vapors, or dusts occur. Electrical equipment that must be installed in such locations is especially designed and tested to ensure it does not initiate an explosion, due to arcing contacts...
, more robust cable protection may be necessary. Common conduit and ductwork protects against direct physical abuse, but is neither air nor water tight. In wet locations, conduit may resemble standard threaded pipe in appearance, with gasketed box openings to keep moisture out. Areas with potentially explosive gases need further protection to prevent electrical sparks from igniting the gases, and internal conduit gas-tight barriers to prevent potentially ignited gases from traveling inside the conduit to other parts of the building.
Actual vs maximum current rating
Nominal Rated
Circuit Capacity |
Continuous Rated
Circuit Capacity |
| 5 amps |
4 amps |
| 10 amps |
8 amps |
| 15 amps |
12 amps |
| 20 amps |
16 amps |
| 30 amps |
24 amps |
| 50 amps |
40 amps |
| 100 amps |
80 amps |
| 200 amps |
160 amps |
Most commonly available circuit breakers are rated to carry no more than 80% of their nominal rating continuously (3 hours or more) (NEC Art. 100). 100%-rated circuit breakers are manufactured for and may carry 100% of their nominal rating continuously.
Temperature rating
The temperature rating of a wire or cable is generally the maximum safe ambient temperature that the wire can carry full-load power without the cable insulation melting, oxidizing, or self-igniting. A full-load wire does heat up slightly due to the metallic resistance of the wire, but this wire heating is factored into the cable's temperature rating. (NEC 310.10)
The NEC specifies acceptable numbers of conductors in crowded areas such as inside conduit, referred to as the
fill rating. If the accepted fill rating is exceeded, then all the cables in the conduit are
derated, lowering their acceptable maximum ambient
operating temperatureAn operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
. Derating is necessary because multiple conductors carrying full-load power generate heat that may exceed the normal insulation temperature rating. (NEC 310.16)
In construction situations where future expansion is highly likely, it is sometimes more economical to install a slightly larger diameter conduit than is necessary for the initial building construction. Larger conduit costs more, but has a greater fill rating. This may eliminate the need for additional conduit installation while maintaining the conduit's overall temperature rating.
In certain situations, the temperature rating can be higher than normal, such as for
knob and tube wiringKnob and tube wiring was an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1930s...
where two or more load-carrying wires are never likely to be in close proximity. A knob and tube installation uses wires that are suspended in air. This gives them a greater heat dissipation rating than standard 3-wire NM-2 cable which includes two tightly bundled load and return wires.
See also
- Canadian Electrical Code
The Canadian Electrical Code, CE code, or CSA C22.1 is a standard published by the Canadian Standards Association pertaining to the installation and maintenance of electrical equipment in Canada....
- PSE law
The is the law that governs electrical appliance safety in Japan. PSE stands for Product Safety Electrical Appliance & Material. The formal name is . The most recent revision comes April 1, 2001. The PSE symbol can be found on appliances that are approved for use in Japan....
, Japan Electrical Safety Law.
- 2008 National Electrical Code (ISBN 978-0877657903)
- 2005 National Electrical Code (ISBN 978-0877656234)
- Top 10 Changes to NE 2011
- Slash rating
The slash rating, under the United States National Electrical Code, is given to circuit interrupt hardware and specifies a maximum line-to-ground voltage rating in combination with a maximum line-to-line voltage rating. One common application would be for a three-phase electrical loads...
External links