NEMA OS 3-2016 Selection and Installation Guidelines for Electrical Outlet Boxes.pdf

1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA OS 3-2016Selection and Installation Guidelines for Electrical Outlet Boxes 2016 National Electrical Manufacturers Association NEMA Standards Publication OS 3-2016 Selection and Installation Guidelines for Electrical Outlet B

2、oxes Published by: National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2016 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Be

3、rne Convention for the Protection of Literary and Artistic Works, and the International and Pan American copyright conventions. 2016 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons en

4、gaged in the development and approval of the document at the time it was developed. Consensus does not necessarily mean that there is unanimous agreement among every person participating in the development of this document. The National Electrical Manufacturers Association (NEMA) standards and guide

5、line publications, of which the document contained herein is one, are developed through a voluntary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA adminis

6、ters the process and establishes rules to promote fairness in the development of consensus, it does not write the document and it does not independently test, evaluate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guidelin

7、e publications. NEMA disclaims liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims a

8、nd makes no guaranty or warranty, express or implied, as to the accuracy or completeness of any information published herein, and disclaims and makes no warranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the perf

9、ormance of any individual manufacturer or sellers products or services by virtue of this standard or guide. In publishing and making this document available, NEMA is not undertaking to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform

10、any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standa

11、rds on the topic covered by this publication may be available from other sources, which the user may wish to consult for additional views or information not covered by this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA

12、does not certify, test, or inspect products, designs, or installations for safety or health purposes. Any certification or other statement of compliance with any health or safetyrelated information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier o

13、r maker of the statement. NEMA OS 3-2016 Page i 2016 National Electrical Manufacturers Association Foreword User input was considered in the development of this standards publication. This standards publication was developed by the NEMA Outlet and Switch Box Section, which periodically reviews it fo

14、r any revisions necessary to address changing conditions, product listing and installation requirements, and technical progress. Comments for proposed revisions are welcomed and should be submitted to: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 17t

15、h Street, Suite 900 Rosslyn, VA 22209 OS 3-2016 revises and supersedes OS 3-2012. This standards publication was developed and approved by the Outlet and Switch Box Section. At the time it was approved, the Outlet and Switch Box Section was composed of the following members: 2D2C, Inc. (Lincolnshire

16、, IL) Appleton Group (Rosemont, IL) Allied Moulded Products, Inc. (Bryan, OH) Arlington Industries, Inc. (Scranton, PA) Bridgeport Fittings, Inc. (Stratford, CT) Eatons B-Line Business (Highland, IL) Crouse-Hinds by Eaton (Syracuse, NY) Hubbell Incorporated (Shelton, CT) Legrand/Pass b) houses and p

17、rovides a degree of mechanical protection for conductor splices and wiring devices such as switches and receptacles; and c) limits access to live parts; and where applicable, bonds electrically conductive components to the equipment grounding conductor. When designed and specifically identified for

18、the purpose, a box and other components form an enclosure system that: a) provides degrees of protection from external environmental conditions (rain, dust, scrub water, etc.); b) preserves the integrity of fire-resistive-rated walls, ceilings, floors, partitions, or furniture in which it is install

19、ed; and/or c) provides independent support for attached products such as luminaires, ceiling-suspended fans, and safety and security devices. For the most part, boxes within the scope of these guidelines fall into just a few general classifications. Each classification has been adapted over the year

20、s to meet market needs. NEMA has written these guidelines to provide qualified designers, installers, and inspectors with an industry perspective of the appropriate selection and installation criteria based on the designed, intended use of the product. The member companies of the NEMA Outlet and Swi

21、tch Box Section promote the selection and installation of listed boxes and covers and listed raceways and fittings. The listing of electrical system components qualifies them to minimum performance requirements and provides for ongoing conformity surveillance. Listed boxes and covers can be recogniz

22、ed by the trademark of the qualified electrical testing laboratory on the part or its smallest unit container. It is our objective to develop a closer liaison with the installers of our products and professional electrical inspectors. Through this liaison, we intend to provide uniform education and

23、understanding as to the intended use and application of our products. Through education, we hope to develop an alliance founded in trust that will ensure that the concerns and challenges we each face are addressed. NEMA OS 3-2016 Page v 2016 National Electrical Manufacturers Association Compatibilit

24、y of Boxes with Metallic and Nonmetallic Wiring SystemsGrounding and Bonding Metal and nonmetallic outlet boxes are typically designed for use in electrical distribution systems rated 600 volts or less. Metal systems and raceways that are recognized as equipment grounding conductors provide protecti

25、on by grounding and bonding the entire system. All the components of the system (boxes, fittings, devices, luminaires or other products, raceways, etc.) with proper installation are designed to maintain continuous grounding and bonding throughout the system. Products must be installed so that the re

26、moval of any device, fixture, or box cover does not interrupt the downstream grounding or bonding path. Nonmetallic systems protect installers and end users by providing isolation (insulation) throughout the wiring system. All the components (boxes, fittings, devices, luminaires or other products, r

27、aceways, etc.) with proper installation are designed to maintain this isolation (insulation). Nonmetallic-sheathed cable (NM cable) is commonly used in the construction of residential and single- and multi-family dwellings. Although changes in cable and cable clamp designs have occurred over the pas

28、t several decades, when system components are properly selected and installed in accordance with the manufacturers instructions and the National Electrical Code(NEC), NM cable systems will continue to be reliable and safe for branch circuit wiring. When properly installed: a) there are no ungrounded

29、 exposed metal parts likely to become energized in case of a ground fault; b) ground wires are installed inside the raceways and throughout the system; and c) ground wires are joined so that removal of a device, luminaire, or other product does not interrupt the downstream ground path. Generally, th

30、is is done by joining the incoming and outgoing ground wires with a third ground wire that then attaches to the device, luminaire, or other product. Thus, the removal of the device, luminaire, or other product does not affect the downstream ground path. Each system is designed to distribute electric

31、al power while protecting installers and end users. Since metallic and nonmetallic systems employ different means to provide protection, for safety reasons, these two systems should not be randomly mixed without due consideration. Where it is necessary and desirable to mix metallic and nonmetallic c

32、omponents in a wiring system, special products, applications, and procedures can be used to ensure the desired level of safety in accordance with the NEC. Outlet Boxes Classified for Fire Resistance Special-purpose floor boxes and poke-through floor fittings for installation through fire-resistive-r

33、ated floor-ceilings and nonmetallic outlet boxes, and switch boxes for installation in fire-resistive-rated wall or partition assemblies are additionally classified for the degree of fire resistance provided by those boxes. Classifications of these boxes for the degree of fire resistance permits coo

34、rdination with the fire-resistive ratings of floor-ceilings, walls, and partition assemblies to maintain the integrity of fire resistance for those particular constructions. These fire-resistive-rated products are intended for use with specific constructions of floor-ceilings, walls, and partition a

35、ssemblies. Floor-ceiling, wall, and partition assemblies are fire resistive based on their construction materials, how they are constructed in method and cross-sectional dimensions, and how their exposed surfaces are finished or coated. These fire-resistive-rated products are in turn limited as to N

36、EMA OS 3-2016 Page vi 2016 National Electrical Manufacturers Association how closely they may be spaced from one another and how many can penetrate any given discrete section of floor-ceiling, wall, or partition assembly without compromising that fire-resistive-rated section. Since the wiring method

37、 and the electrical conductors to those boxes and poke-through fittings can directly affect thermal conduction through those sections of floor-ceilings, walls, and partition assemblies, the classification of fire-resistive boxes and poke-through floor fittings often impose limitations on eligible wi

38、ring methods and on conductor count and size. Full details and limitations on the application of a box classified for use in a fire-resistive assembly can be referenced in the UL Fire Resistance Directory. Product Standards and Installation Codes Boxes and covers within the scope of these guidelines

39、 are designed for installation in compliance with NFPA 70 NEC. The broadest range of general-purpose designs is included in ANSI/NEMA OS 1 Sheet-Steel Outlet Boxes, Device Boxes, Covers, and Box Supports and ANSI/NEMA OS 2 Nonmetallic Outlet Boxes, Device Boxes, Covers, and Box Supports. ANSI/NEMA F

40、B 1 Fittings, Cast Metal Boxes, and Conduit Bodies for Conduit, Electrical Metallic Tubing, and Cable contains those boxes described in its title, and ANSI/NEMA WD 6 Wiring DevicesDimensional Specifications includes flush-device cover plates. Conformity to these standards provides assurance of the c

41、ompatibility and interchangeability of box designs with covers, raceways, wiring devices, and other components of the electrical distribution system whose performance may be dependent on the box design. Listed boxes are typically evaluated to the safety and performance requirements of ANSI/UL 514A M

42、etallic Outlet Boxes or ANSI/UL 514C Nonmetallic Outlet Boxes, Flush-Device Boxes, and Covers. The safety and performance requirements for flush-device cover plates reside in ANSI/UL 514D Cover Plates for Flush-Mounted Wiring Devices. Boxes intended to provide degrees of protection from external env

43、ironmental conditions may also be subject to the requirements found in NEMA 250 Enclosures for Electrical Equipment (1000 Volts Maximum) or ANSI/UL 50E Enclosures for Electrical Equipment, Environmental Considerations. Floor boxes and poke-through floor fittings intended to be installed in fire-resi

44、stive-rated floor-ceiling sections and nonmetallic boxes intended to be installed in fire-resistive-rated walls, ceilings, floors, partitions, or furniture must also be separately evaluated to establish a rating classification in accordance with ANSI/UL 263 Fire Tests of Building Construction and Ma

45、terials and ASTM E 119 Standard Test Methods for Fire Tests of Building Construction and Materials. Nonmetallic boxes so classified must also be evaluated in accordance with Supplement SB Nonmetallic Boxes for Installation in Fire Resistance Rated Wall and Partition Assemblies of ANSI/UL 514C Nonmet

46、allic Outlet Boxes, Flush-Device Boxes, and Covers. Given that all listed boxes have met the same minimum safety and performance requirements, selection of the right box for the application is the single most important factor for safe, effective, and permanent installations. Design preference comple

47、tes the selection process, as there are many optional features that distinguish alternative brands. Beyond selection, almost every other variable comes down to good workmanship, something every craftsman takes pride in and that is fundamentally required by the NEC. Note: All references to the NEC ar

48、e to the 2017 edition. Coordination of Trades With regard to workmanship, the quality of a box installation can be seriously compromised when no effort is made to coordinate the installation of electrical outlet boxes with other construction trades. In particular, installation problems have been evi

49、denced where there was insufficient coordination with the trades that apply finished surfaces (drywall) and poured concrete (concrete boxes and floor boxes). Every effort should be made to coordinate with these and other trades, since lack of careful consideration may compromise the safety or quality of an installation. NEMA OS 3-2016 Page 1 2016 National Electrical Manufacturers Association Section 1 Product Selection 1.1 General The three key elements to the selection of an electrical outlet box are: a) Type of wiring system b) Contents and function after installation c)