Article 90
Wiring Planning
A. Future Expansion and Convenience. Plans and specifications that provide ample space and raceways, spare raceways, and additional spaces allow for future increases in electrical power and communication circuits. Distribution centers located in readily accessible locations provide convenience and safety of operation. B. Number of Circuits in Enclosures. It is elsewhere provided in this code that the number of wires and circuits confined in a single enclosure be varyingly restricted. Limiting the number of circuits in a single enclosure minimize the effects of from a short-circuit or groundfault in one circuit.
Explanatory Materials
Explanatory material such as references or 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. Such notes are informational only and are not enforcable as requirements of this code.
Mandatory Rules
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.
Informative Annexes
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.
Permissive Rules
Permissive rules of this code are those that identify actions that are allowed but not required, are normally use to describe options or alternative methods, and are characterized by the use of the terms shall be permitted or shall not be required.
Special Permission
The authority having jurisdiction for enforcing this called may grant exception for the installation of conductors and equipment that are not under the exclusive control of the electric utilities and are used to connect electric utility supply system to the service conductors of the premises served, provided such installations are outside of the building or structure, or to terminate inside the nearest point of entrance of the service conductors.
Practical Safeguarding
The purpose of this code is the practical safeguarding of persons and property from hazards arising from the use of electricity.
Covered
This code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following: 1. Public and private premises, including buildings, structures, Mobile homes, recreational vehicles, and floating buildings 2. Yards, lots, parking lots, carnivals, and industrial sub stations. 3. Installation of conductors and equipment that connect to the supply of electricity. 4. Installations used by the electrical utility, such as office buildings, warehouses, garages, machine shops, and re-creational buildings, that are not an integral part of a generating plant, substation, or control center.
Not Covered
This code does not cover the following: 1. Installation in ships, watercraft other then floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and re-creation old vehicles. 2. Installations underground in mines and self propelled mobile surface mining machinery and it's attendant electrical trailing cable. 3. Installations of railways for generation, transformation, transmission, or distribution of power used exclusively for operation of rolling stock or installations used exclusively for signaling and communications purposes. 4. Installations of communications equipment under the exclusive control of communications utilities located outdoors or in building spaces used exclusively for such installations. 5. Installations under the exclusive control of an electric utility where such installations a. Consist of service drops or service laterals, and Associated metering or b. Are on property owned or leased by the electric utility for the purpose of communications, metering, generation, control, transformation, transmission, or distribution of electrical energy or c. Are located in legally established easements or rights of way or d. Are located by other reading agreements either designated by or recognized by public service commission's, 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, or distribution of electrical 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 US 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.
Enforcement
This code is intended to be suitable for mandatory application by governmental bodies that exercise legal jurisdiction over electrical installations, including signaling and communication 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.
Intention
This code is not intended as a design specification or an instructional manual for untrained persons.
Code Arrangement
This cold is divided into the introduction and then chapters 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. These latter chapters supplement or modify the general rules. Chapter 1 through 4 apply except as amended by chapters 5,6, and 7 for the particular conditions. Chapter 8 covers communications. Chapter 9 consists of tables that are applicable as referenced.
Formal Interpretations
To promote uniformity of interputation and application of the provisions of this code, formal interpretation procedures have been established and are found in the NFPA Regulations Governing Committee Projects.