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ons of the NEC are outlined in Section 6 of the NFPA Regulations Governing the Development of NFPA Standards. These regulations are included in the NFPA Standards Directory, which is published annually and can be found at nfpa.org/regs. 90.7 Exam...

ons of the NEC are outlined in Section 6 of the NFPA Regulations Governing the Development of NFPA Standards. These regulations are included in the NFPA Standards Directory, which is published annually and can be found at nfpa.org/regs. 90.7 Examination of Equipment for Safety. 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. Informational Note No. 2: See Article 100for definitions of Listed and Reconditioned. Informational Note No. 3: See Informative Annex A for a list of product safety standards that are compatible with this Code. ENHANCED CONTENT Collapse Testing laboratories, inspection agencies, and other organizations concerned with product evaluation publish lists of equipment and materials that have been tested and meet nationally recognized standards or that have been found suitable for use in a specified manner. The NEC does not contain detailed information on equipment or materials but refers to products as listed, labeled, or identified. See Article 100 for definitions. Many certification agencies also perform field evaluations of specific installations in order to render an opinion on compliance with NEC requirements along with any applicable product standards. NFPA 790, Standard for Competency of Third-Party Field Evaluation Bodies, provides requirements for the qualification and competence of a body performing field evaluations on electrical products and assemblies with electrical components. NFPA 791, Recommended Practice and Procedures for Unlabeled Electrical Equipment Evaluation, covers recommended procedures for evaluating unlabeled electrical equipment for compliance with nationally recognized standards and with any requirements of the AHJ. NFPA does not approve, inspect, or certify any installations, procedures, equipment, or materials, nor does it approve or evaluate testing laboratories. In determining the acceptability of installations or procedures, equipment, or materials, the AHJ may base acceptance on compliance with NFPA or other appropriate standards. The AHJ may also refer to the listing or labeling practices of an organization concerned with product evaluations to help determine compliance with appropriate standards. Informative Annex A contains a list of product safety standards used for product listing. The list includes product safety standards for which a listing is required by the NEC. For example, 344.6 requires that rigid metal conduit, RMC, be listed. By using Informative Annex A, the user finds that the listing standard for rigid metal conduit is UL 6, Electrical Rigid Metal Conduit — Steel. Because associated conduit fittings are required to be listed, UL 514B, Conduit, Tubing, and Cable Fittings, is found in Informative Annex A also. 90.8 Wiring Planning. (A) Future Expansion and Convenience. 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. ENHANCED CONTENT Collapse Consideration should always be given to future expansion of the electrical system. Future expansion might be unlikely in some occupancies. In other occupancies, however, it might be cost effective to plan for future additions, alterations, or designs during initial installation. The requirement for providing the exclusively dedicated equipment space mandated by 110.26(E) supports the intent of 90.8(A) regarding future increases in the use of electricity. Communications circuits are important to consider when planning for future needs. Electrical distribution centers should contain additional space and capacity for future additions and should be located for easy accessibility. In commercial and industrial facilities, a common and cost-effective practice is to purchase switchboards with additional capacity to accommodate future expansion, as shown below. (Courtesy of the International Association of Electrical Inspectors) Number of Circuits in Enclosures. 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. 90.9 Units of Measurement. (A) Measurement System of Preference. 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). Dual System of Units. 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. (C) Permitted Uses of Soft Conversion. The cases given in 90.9(C)(1) through (C)(4) shall not be required to use hard conversion and shall be permitted to use soft conversion. Trade Sizes. 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. Extracted Material. 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. Industry Practice. Where industry practice is to express units in inch-pound units, the inclusion of SI units shall not be required. Safety. Where a negative impact on safety would result, soft conversion shall be used. Compliance. 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. ENHANCED CONTENT Collapse Soft conversions are numerically accurate. Hard conversions are rounded or approximate values of the customary unit dimension. Soft conversions are required when an approximation would negatively impact safety. The table below offers examples of the hard conversion process. The conversion of the U.S. customary units into metric equivalents shows the small variance between soft conversions and hard conversions. Article 100 Definitions Scope. This article contains only those definitions essential to the application of this Code. It is not intended to include commonly defined general terms or commonly defined technical terms from related codes and standards. An article number in parentheses following the definition indicates that the definition only applies to that article. Informational Note: A definition that is followed by a reference in brackets has been extracted from one of the following standards. Only editorial changes were made to the extracted text to make it consistent with this Code. NFPA 30A-2021, Code for Motor Fuel Dispensing Facilities and Repair Garages NFPA 33-2021, Standard for Spray Application Using Flammable or Combustible Materials NFPA 75-2020, Standard for the Fire Protection of Information Technology Equipment NFPA 79-2021, Electrical Standard for Industrial Machinery NFPA 99-2021, Health Care Facilities Code NFPA 101®-2022, Life Safety Code® NFPA 110-2019, Standard for Emergency and Standby Power Systems NFPA 303-2021, Fire Protection Standard for Marinas and Boatyards NFPA 307-2021, Standard for the Construction and Fire Protection of Marine Terminals, Piers, and Wharves NFPA 499-2021, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas NFPA 501-2022, Standard on Manufactured Housing NFPA 790-2021, Standard for Competency of Third-Party Field Evaluation Bodies NFPA 1192-2021, Standard on Recreational Vehicles ENHANCED CONTENT Collapse The NEC defines a number of technical terms in order to provide a common understanding of their use within the NEC. All definitions throughout the NEC have been relocated to Article 100, based on revisions within the 2020 NEC Style Manual. According to the revised NEC Style Manual section 2.2.2, all definitions are required to reside in Article 100, and Article 100 is not permitted to be subdivided. Any definitions that apply in only one article will have the article number in parentheses following the definition. If a specific article does not follow the definition in parentheses, then the definition applies throughout the NEC. The Code Making Panel (CMP) responsible for the definition is also listed at the end of the definition. The NEC does not define every term used. General terms are found in nontechnical dictionaries. Some technical terms are used as defined in Institute of Electrical and Electronics Engineers (IEEE) 100, The Authoritative Dictionary of IEEE Standards Terms. It is important to note that many terms used in the electrical trades are actually registered trademarks for specific products or lines of products. Trademarked terms are not used in the NEC or this handbook. Accessible (as applied to equipment). Capable of being reached for operation, renewal, and inspection. (CMP-1) ENHANCED CONTENT Collapse The following exhibit illustrates equipment considered accessible (as applied to equipment) in accordance with requirements elsewhere in the NEC. The requirement for the accessibility of switches and circuit breakers used as switches is shown in (a) and is according to 404.8(A). In (b), the busway installation is according to 368.17(C). The busway switches installation shown in (c), the switch installation adjacent to a motor in (d), and the hookstick-operated isolating switch installation in (e) are according to the exceptions in the list items of 404.8(A). Accessible (as applied to wiring methods). Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in or blocked by the structure, other electrical equipment, other building systems, or finish of the building. (CMP-1) ENHANCED CONTENT Collapse Wiring methods located behind removable panels designed to allow access are not considered permanently enclosed and are considered exposed (as applied to wiring methods). The exhibit below shows an example of wiring methods and equipment that are considered accessible despite being located above a suspended ceiling. See also 300.4(C) regarding cables located in spaces behind accessible panels. Accessible, Readily (Readily Accessible). Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to take actions such as to use tools (other than keys), to climb over or under, to remove obstacles, or to resort to portable ladders, and so forth. (CMP-1) Informational Note: Use of keys is a common practice under controlled or supervised conditions and a common alternative to the ready access requirements under such supervised conditions as provided elsewhere in the NEC. ENHANCED CONTENT Collapse Locks are commonly used on electrical equipment and electrical equipment rooms to keep unauthorized persons away from electrical hazards and to prevent tampering. The definition of readily accessible does not preclude the use of locks on service equipment doors or doors of rooms containing service equipment, provided a key or lock combination is available to those for whom ready access is necessary. If a tool is necessary to gain access, the equipment is not readily accessible. Sections 230.70(A)(1) and 235.352(A) require service disconnecting means to be readily accessible. However, 235.352(A) permits a mechanical linkage or, in multibuilding industrial installations under single management, a remote-control device in a separate building or structure to provide an equivalent to access. Adapter. A device used to adapt a circuit from one configuration of an attachment plug or receptacle to another configuration with the same current rating. (520) (CMP-15) Adjustable Speed Drive. Power conversion equipment that provides a means of adjusting the speed of an electric motor. (CMP-11) Informational Note: A variable frequency drive is one type of electronic adjustable speed drive that controls the rotational speed of an ac electric motor by controlling the frequency and voltage of the electrical power supplied to the motor. Adjustable Speed Drive System. A combination of an adjustable speed drive, its associated motor(s), and auxiliary equipment. (CMP-11) Aircraft Painting Hangar. An aircraft hangar constructed for the express purpose of spraying, coating, and/or dipping applications and provided with dedicated ventilation supply and exhaust. (CMP-14) Alternate Power Source. One or more generator sets, or battery systems where permitted, intended to provide power during the interruption of the normal electrical service; or the public utility electrical service intended to provide power during interruption of service normally provided by the generating facilities on the premises. [99:3.3.4] (517) (CMP-15) ENHANCED CONTENT Collapse See also 517.30(B), which identifies the permitted types of power sources for the essential electrical system (EES) in health care facilities, and 517.31(B)(2), which permits alternate power sources to serve essential electrical systems of contiguous or multiple building facilities such as a health care campus with a centrally located alternate power plant. Ambulatory Health Care Occupancy. An occupancy used to provide services or treatment simultaneously to four or more patients that provides, on an outpatient basis, one or more of the following: Treatment for patients that renders the patients incapable of taking action for self-preservation under emergency conditions without the assistance of others. Anesthesia that renders the patients incapable of taking action for self-preservation under emergency conditions without the assistance of others. Treatment for patients who, due to the nature of their injury or illness, are incapable of taking action for self-preservation under emergency conditions without the assistance of others. [101:3.3.198.1] (517) (CMP-15) ENHANCED CONTENT Collapse Ambulatory health care occupancies, including outpatient surgery centers, freestanding emergency medical centers, and hemodialysis units, are subject to the requirements of Part II of Article 517 and 517.45. This definition, which correlates with NFPA 99, Health Care Facilities Code, recognizes that some emergency or urgent care is performed at ambulatory health care occupancies. Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. (CMP-6) ENHANCED CONTENT Collapse “Conditions of use” include factors such as ambient temperature and the number of conductors in the cable or raceway. A conductor with insulation rated at 60°C and installed near a furnace where the ambient temperature is continuously maintained at 60°C has no current-carrying capacity. Any current flowing through the conductor will raise its temperature above the 60°C insulation rating. Therefore, the ampacity of the conductor, regardless of its size, is zero. Additional conductors in a raceway or cable raise the temperature in the raceway, decreasing the available ampacity. [See 310.15(C)(1).] For more on the temperature limitation of conductors, see 310.15(B)(1). For the ampacity correction factors for temperature, see Table 310.15(B)(1)(1), Table 310.15(B)(1)(2), and Informative Annex B. Amplifier (Audio Amplifier) (Pre-Amplifier). Electronic equipment that increases the current or voltage, or both, of an audio signal intended for use by another piece of audio equipment. Amplifier is the term used to denote an audio amplifier. (640) (CMP-12) Appliance. Utilization equipment, generally other than industrial, that is fastened in place, stationary, or portable; is normally built in a standardized size or type; and is installed or connected as a unit to perform one or more functions such as clothes washing, air-conditioning, food mixing, deep frying, and so forth. (CMP-17) Applicator. The device used to transfer energy between the output circuit and the object or mass to be heated. (665) (CMP-12) Approved. Acceptable to the authority having jurisdiction. (CMP-1) ENHANCED CONTENT Collapse Typically, approval of listed equipment is more readily given by an authority having jurisdiction (AHJ) if the authority accepts a laboratory’s listing mark. Other options may be available for the jurisdiction to approve equipment, including evaluation by the inspection authority or field evaluation by a qualified laboratory or individual. Where an evaluation is conducted on site, industry standards such as NFPA 79, Electrical Standard for Industrial Machinery, if applicable, can be used. NFPA 790, Standard for Competency of Third-Party Field Evaluation Bodies, can be used to qualify evaluation services. NFPA 791, Recommended Practice and Procedures for Unlabeled Electrical Equipment Evaluation, can be used to evaluate unlabeled equipment in accordance with nationally recognized standards and any requirements of the AHJ. See also 110.2, 110.3, and the definition of authority having jurisdiction (AHJ) for more information on the approval process. See the definitions of field evaluation body and field labeled for information on this option for product approval by the AHJ. Arc-Fault Circuit Interrupter (AFCI). A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected. (CMP-2) ENHANCED CONTENT Collapse Arc-fault circuit interrupters (AFCIs) are evaluated in accordance with UL 1699, Standard for Arc-Fault Circuit-Interrupters, using testing methods that create or simulate arcing conditions to determine a product’s ability to detect and interrupt arcing faults. AFCIs are also tested to verify that arc detection is not inhibited by the presence of loads and circuit characteristics that mask the hazardous arcing condition. In addition, these devices are evaluated to determine resistance to unwanted tripping due to the presence of arcing that occurs in equipment under normal operating conditions or to a loading condition that closely mimics an arcing fault, such as a solid-state electronic ballast or a dimmed load. Array. A mechanically and electrically integrated grouping of modules with support structure, including any attached system components such as inverter(s) or dc-to-dc converter(s) and attached associated wiring. (690) (CMP-4) ENHANCED CONTENT Collapse An example of an array composed of multiple panels installed on a support structure is pictured below. (Courtesy of Solar Design Associates, LLC) Askarel. A generic term for a group of nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. (CMP-9) Informational Note: Askarels of various compositional types are used. Under arcing conditions, the gases produced, while consisting predominantly of noncombustible hydrogen chloride, can include varying amounts of combustible gases, depending on the askarel type. Associated Apparatus. Apparatus in which the circuits are not necessarily intrinsically safe themselves but that affects the energy in the intrinsically safe circuits and is relied on to maintain intrinsic safety. Such apparatus is one of the following: Electrical apparatus that has an alternative type of protection for use in the appropriate hazardous (classified) location Electrical apparatus not so protected that shall not be used within a hazardous (classified) location (CMP-14) Informational Note No. 1: Associated apparatus has