This article covers use and application, arrangement, and enforcement of this Code. It also covers the expression of mandatory, permissive, and nonmandatory text, provides guidance on the examination of equipment and on wiring planning, and specifies the use and expression of measurements.
The purpose of this Code is the
practical safeguarding of persons and property from hazards
arising from the use of electricity. This Code is not intended as a
design specification or an instruction manual for untrained
persons.
This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.
Informational Note: Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes provide for future increases in the use of electricity.
This Code covers the installation
and removal of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and
raceways; and optical fiber cables for the following:
Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating
buildings
Yards, lots, parking lots, carnivals, and industrial substations
Installations of conductors and equipment that connect
to the supply of electricity
Installations used by the electric utility, such as office
buildings, warehouses, garages, machine shops, and
recreational buildings, that are not an integral part of a
generating plant, substation, or control center
Installations supplying shore power to ships and watercraft in marinas and boatyards, including monitoring of
leakage current
Installations used to export electric power from vehicles
to premises wiring or for bidirectional current flow
Installations in ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles
Informational Note: Although the scope of this Code indicates that the Code does not cover installations in ships, portions of this Code are incorporated by reference into Title 46, Code of Federal Regulations, Parts 110-113.
Installations underground in mines and self-propelled mobile surface mining machinery and its attendant electrical trailing cable
Installations of railways for generation, transformation, transmission, energy storage, or distribution of power used exclusively for operation of rolling stock or installations used exclusively for signaling and communications purposes
Are on property owned or leased by the electric utility for the purpose of communications, metering, generation, control, transformation, transmission, energy storage, or distribution of electric energy, or
Are located in legally established easements or rights-of-way, or
Are located by other written agreements either designated by or recognized by public service commissions, utility commissions, or other regulatory agencies having jurisdiction for such installations. These written agreements shall be limited to installations for the purpose of communications, metering, generation, control, transformation, transmission, energy storage, or distribution of electric energy where legally established easements or rights-of-way cannot be obtained. These installations shall be limited to federal lands, Native American reservations through the U.S. Department of the Interior Bureau of Indian Affairs, military bases, lands controlled by port authorities and state agencies and departments, and lands owned by railroads.
Informational Note to (4) and (5): Examples of utilities may include those entities that are typically designated or recognized by governmental law or regulation by public service/utility commissions and that install, operate, and maintain electric supply (such as generation, transmission, or distribution systems) or communications systems (such as telephone, CATV, Internet, satellite, or data services). Utilities may be subject to compliance with codes and standards covering their regulated activities as adopted under governmental law or regulation. Additional information can be found through consultation with the appropriate governmental bodies, such as state regulatory commissions, the Federal Energy Regulatory Commission, and the Federal Communications Commission.
The requirements in this Code address the fundamental principles of protection for safety contained in Section 131 of International Electrotechnical Commission Standard 60364-1, Low-voltage Electrical Installations - Part 1: Fundamental Principles, Assessment of General Characteristics, Definitions.
Informational Note: See IEC 60364-1, Low-voltage Electrical Installations — Part 1: Fundamental Principles, Assessment of General Characteristics, Definitions, Section 131, for fundamental principles of protection for safety that encompass protection against electric shock, protection against thermal effects, protection against overcurrent, protection against fault currents, and protection against overvoltage. All of these potential hazards are addressed by the requirements in this Code.
This Code is divided into the introduction and nine chapters, as shown in Figure 90.3. Chapters 1,
2, 3, and 4 apply generally. Chapters 5, 6, and 7 apply to special
occupancies, special equipment, or other special conditions
and may supplement or modify the requirements in Chapters 1
through 7.
Chapter 8 covers communications systems and is not subject
to the requirements of Chapters 1 through 7 except where the
requirements are specifically referenced in Chapter 8.
Chapter 9 consists of tables that are applicable as referenced.
Informative annexes are not part of the requirements of this
Code but are included for informational purposes only.
This Code is intended to be suitable for
mandatory application by governmental bodies that exercise
legal jurisdiction over electrical installations, including signaling and communications systems, and for use by insurance
inspectors.
The authority having jurisdiction for
enforcement of the Code has the responsibility for making
interpretations of the rules, for deciding on the approval of
equipment and materials, and for granting the special permission contemplated in a number of the rules.
By
special permission, the authority having jurisdiction may waive
specific requirements in this Code or permit alternative methods where it is assured that equivalent objectives can be
achieved by establishing and maintaining effective safety.
This Code may require new products, constructions, or materials that may not yet be available at the time the Code is adopted. In such event, the authority having jurisdiction may permit the use of the products, constructions, or materials that comply with the most recent previous edition of this Code adopted by the jurisdiction.
Informational Note: See Informative Annex H, Administration and Enforcement, for a model of guidelines that can be used to create an electrical inspection and enforcement program and to adopt NFPA 70, National Electrical Code.
Mandatory rules of this Code are those
that identify actions that are specifically required or prohibited
and are characterized by the use of the terms shall or shall not.
Permissive rules of this Code are those that identify actions that are allowed but not required, are normally used to describe options or alternative methods, and are characterized by the use of the terms shall be permitted or shall not be required.
Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of informational notes or an informative annex. Unless the standard reference includes a date, the reference is to be considered as the latest edition of the standard. Such notes are informational only and are not enforceable as requirements of this Code.
Brackets containing section references to another NFPA document are for informational purposes only and are provided as a guide to indicate the source of the extracted text. These bracketed references immediately follow the extracted text.
Informational Note: The format and language used in this Code follows guidelines established by NFPA and published in the NEC Style Manual. Copies of this manual can be obtained from NFPA.
Nonmandatory information relative to the use of the NEC is provided in informative annexes. Informative annexes are not part of the enforceable requirements of the NEC, but are included for information purposes only.
To promote uniformity of interpretation and application of this Code, formal interpretation
procedures have been established and are found in the Regulations Governing the Development of NFPA Standards.
For specific items of equipment and materials referred to in this Code, examinations for safety made under standard conditions provide a basis for approval where the record is made generally available through promulgation by organizations properly equipped and qualified for experimental testing, inspections of the run of goods at factories, and service-value determination through field inspections. This avoids the necessity for repetition of examinations by different examiners, frequently with inadequate facilities for such work, and the confusion that would result from conflicting reports on the suitability of devices and materials examined for a given purpose.
It is the intent of this Code that factory-installed internal wiring or the construction of equipment need not be inspected at the time of installation of the equipment, except to detect alterations or damage, if the equipment has been listed by a qualified electrical testing laboratory that is recognized as having the facilities described in the preceding paragraph and that requires suitability for installation in accordance with this Code. Suitability shall be determined by application of requirements that are compatible with this Code.
Informational Note No. 1: See 110.3 for guidance on safety examinations.
Plans and specifications that provide ample space in raceways, spare raceways, and additional spaces allow for future increases in electric power and communications circuits. Distribution centers located in readily accessible locations provide convenience and safety of operation.
It is elsewhere provided
in this Code that the number of circuits confined in a single
enclosure be varyingly restricted. Limiting the number of
circuits in a single enclosure minimizes the effects from a short
circuit or ground fault.
For the purpose of
this Code, metric units of measurement are in accordance with
the modernized metric system known as the International
System of Units (SI).
SI units shall appear first, and inch-pound units shall immediately follow in parentheses. Conversion from inch-pound units to SI units shall be based on hard conversion except as provided in 90.9(C).
Exception: The tables located in Informative Annex C shall be permitted to list the trade sizes before SI units.
Where the actual measured size of a product is not the same as the nominal size, trade size designators shall be used rather than dimensions. Trade practices shall be followed in all cases.
Where material is extracted from another standard, the context of the original material shall not be compromised or violated. Any editing of the extracted text shall be confined to making the style consistent with that of the NEC.
Conversion from inch-pound units to SI units shall be permitted to be an approximate conversion. Compliance with the numbers shown in either the SI system or the inch-pound system shall constitute compliance with this Code.
Informational Note No. 1: Hard conversion is considered a change in dimensions or properties of an item into new sizes that might or might not be interchangeable with the sizes used in the original measurement. Soft conversion is considered a direct mathematical conversion and involves a change in the description of an existing measurement but not in the actual dimension.
Informational Note No. 2: SI conversions are based on IEEE/ASTM SI 10-1997, Standard for the Use of the International System of Units (SI): The Modern Metric System.
