NEMA OS 3-2012 Selection and Installation Guidelines for Electrical Outlet Boxes.pdf

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1、 NEMA OS 3-2012 Selection and Installation Guidelines for Electrical Outlet Boxes NEMA OS 3-2012 Selection and Installation Guidelines for Electrical Outlet Boxes Published by: National Electrical Manufacturers Association 1300 North 17thStreet Rosslyn, Virginia 22209 www.nema.org Copyright 2013 by

2、the National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American Copyright Conventions. NEMA OS

3、3-2012 Page ii Copyright 2013 by National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons engaged in the development and approval of the document at the time it was developed. Consensus does n

4、ot 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 guideline publications, of which the document contained herein is one, are developed through a voluntary

5、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 administers the process and establishes rules to promote fairness in the development of consensus, it does

6、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 guideline publications. NEMA disclaims liability for any personal injury, property, or other damages of any

7、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 and makes no guaranty or warranty, express or implied, as to the accuracy or completeness of any info

8、rmation 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 performance of any individual manufacturer or sellers products or services by virtue of this standard or

9、 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 any duty owed by any person or entity to someone else. Anyone using this document should rely on his

10、 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 standards on the topic covered by this publication may be available from other sources, which the user may

11、 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 does not certify, test, or inspect products, designs, or installations for safety or health purposes

12、. 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 or maker of the statement. NEMA OS 3-2012 Page iii Copyright 2013 by National Electrical Manufacturer

13、s Association FOREWORD User input has been considered in the development of this standards publication. The standards publication was developed by the NEMA Outlet and Switch Box Section, which periodically reviews it for any revisions necessary to address changing conditions, product listing and ins

14、tallation 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 17th Street Rosslyn, VA 22209 OS 3-2012 revises and supersedes OS 3-2007. This standa

15、rds publication was developed and approved by the Outlet and Switch Box Section. Section approval does not necessarily imply that all section members voted for its approval or participated in its development. At the time it was approved, the Outlet and Switch Box Section was composed of the followin

16、g members: 2D2C, Inc. Lincolnshire, IL Allied Moulded Products, Inc. Bryan, OH Arlington Industries, Inc. Scranton, PA Bridgeport Fittings, Inc. Bridgeport, CTCooper B-Line Highland, IL Cooper Crouse-Hinds Syracuse, NY Emerson/EGS Electrical Group Rosemont, IL ERICO Solon, OH Hubbell Incorporated Sh

17、elton, CT Legrand/Electrical Wiring Systems Division Syracuse, NY RACO South Bend, IN Sigma Electric Manufacturing Corporation Garner, NC Southwire Company Carrollton, GA Thomas 2) houses and provides a degree of mechanical protection for conductor splices, and wiring devices such as switches and re

18、ceptacles; and 3) limits access to live parts; and where applicable, bonds electrically conductive components to the equipment grounding conductor. When designed and specifically identified for the purpose, a box and other components form an enclosure system which: 1) Provides degrees of protection

19、from external environmental conditions (rain, dust, scrub water, etc); 2) preserves the integrity of fire resistance rated walls, ceilings, floors, partitions, or furniture in which it is installed; and/or, 3) provides independent support for attached products such as luminaires, ceiling suspended f

20、ans, 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 years to meet market needs. NEMA has written these guidelines to provide qualified designers, installers, an

21、d 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 Switch Box Section promote selection and installation of listed boxes and covers, and listed raceways and f

22、ittings. Listing of electrical system components qualifies them to minimum performance requirements and provides for ongoing conformity surveillance. Listed boxes and covers can be recognized by the trademark of the qualified electrical testing laboratory on the part or its smallest unit container.

23、It is our objective to develop a closer liaison with the installers of our products and the professional electrical inspector. Through this liaison, we intend to provide uniform education and understanding as to the intended use and application of our products. Through education, we hope to develop

24、an alliance founded in trust that will ensure that the concerns and challenges we each face are addressed. Compatibility of Boxes with Metallic and Nonmetallic Wiring SystemsGrounding and Bonding Metal and nonmetallic outlet boxes are typically designed for use in electrical distribution systems rat

25、ed 600 volts or less. Metal systems and raceways that are recognized as equipment grounding conductors provide protection 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

26、 designed to maintain continuous grounding and bonding throughout the system. Products must be installed so that the removal of any device, fixture or box cover does not interrupt the downstream grounding or bonding path. Nonmetallic systems protect the installer and end users by providing isolation

27、 (insulation) throughout the wiring system. All the components (boxes, fittings, devices, luminaires or other products, raceways, etc.) with proper installation are designed to maintain this isolation (insulation). NEMA OS 3-2012 Page vii Copyright 2013 by National Electrical Manufacturers Associati

28、on Nonmetallic-sheathed cable (NM cable) is commonly used in the construction of residential, single, and multi-family dwellings. Although changes in cable and cable clamp designs have taken place over the past several decades, when system components are properly selected and installed in accordance

29、 with manufacturers instructions and in accordance with the National Electrical Code, NM cable systems will continue to be reliable and safe for branch circuit wiring. When properly installed: a. There are no ungrounded exposed metal parts likely to become energized in case of a ground fault; b. gro

30、und 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, this is done by joining the incoming and outgoing ground wires with a third ground

31、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 electrical power while protecting the installer and end users. Metallic and nonmetallic syst

32、ems employ different means to provide protection. Therefore 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 components in a wiring system, special products, applications, and procedures

33、can be used to ensure the desired level of safety in accordance with the National Electrical Code. Outlet Boxes Classified for Fire Resistance Special-purpose floor boxes and poke-through floor fittings for installation through fire-resistive rated floor-ceilings and nonmetallic outlet boxes and swi

34、tch 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 coordination with the fire-resistive ratings of floor-ceilin

35、gs, walls, or 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, or partition assemblies. Eligible floor-ceilings, walls, and partition as

36、semblies are detailed as to what construction materials are permitted to be employed, as to how they are constructed in method and cross-sectional dimensions, and as to how they are finished or coated on exposed surfaces. These fire-resistive rated products are in turn limited as to how closely they

37、 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 and the electrical conductors to those boxes and poke-through fittings can directly affe

38、ct thermal conduction through those sections of floor-ceilings, walls, or partition assemblies, often the classification of fire-resistive boxes and poke-through floor fittings impose limitations on eligible wiring methods and on conductor count and size. Full details and limitations of the applicat

39、ion 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 are designed for installation in compliance with NFPA 70 National Electrical Code(NEC). T

40、he 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 FB 1 Fittings, Cast NEMA OS 3-2012 Page viii Copyright 2012 by th

41、e National Electrical Manufacturers Association. Metal Boxes, and Conduit Bodies for Conduit, Tubing, and Cable Assemblies contains those boxes described in its title, and ANSI/NEMA WD 6 Wiring DevicesDimensional Requirements includes flush-device cover plates. Conformity to these standards provides

42、 assurance of the compatibility 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

43、 of ANSI/UL 514A Metallic 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 Covers for Flush-Mounted Wiring Devices. Boxes intended to provide degrees of protection from

44、external environmental conditions may also be subject to the requirements found in ANSI/NEMA 250 Enclosures for Electrical Equipment (1000 Volts Maximum) or ANSI/UL 50E, Enclosures for Electrical EquipmentEnvironmental Considerations. Floor boxes and poke-through floor fittings intended to be instal

45、led in fire-resistive rated floor-ceiling sections and nonmetallic boxes intended to be installed in fire resistant 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 Con

46、struction and Materials 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 ANS

47、I/UL 514C Nonmetallic 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 p

48、reference completes 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 NECg147. Note: All refe

49、rences to the NECare to the 2011 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 evidenced 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