NEMA FB 2 20-2014 Selection and Installation Guidelines for Fittings for Use with Flexible Electrical Conduit and Cable.pdf

1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA FB 2.20-2014Selection and InstallationGuidelines for Fittingsfor Use with FlexibleElectrical Conduitand CableNEMA Standards Publication FB 2.20-2014 Selection and Installation Guidelines for Fittings for Use with Flexible El

2、ectrical Conduit and Cable Published by: National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2014 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyr

3、ight Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American copyright conventions. 2014 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the

4、consensus of persons engaged 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 (NE

5、MA) standards and guideline 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 publicat

6、ion. While NEMA administers 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

7、 standards and guideline 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 doc

8、ument. NEMA disclaims and 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 undertak

9、e to guarantee the performance 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

10、undertaking to perform 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. Infor

11、mation and other standards 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

12、of this document. NEMA 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 safety-related information in this document shall not be attributable to NEMA and is solely the responsi

13、bility of the certifier or maker of the statement. NEMA FB 2.20-2014 Page i 2014 National Electrical Manufacturers Association Foreword The selection and installation guidelines provided herein offer practical information on correct product selection and industry recommend practices for the installa

14、tion of fittings for flexible conduit or cable in accordance with the National Electrical Code. These guidelines have been developed and approved by the NEMA Conduit Fittings Section, which periodically reviews them for any revisions necessary to address changing conditions, product listing and inst

15、allation requirements, and technical progress. Section approval of the standard does not necessarily imply that all section members voted for its approval or participated in its development. Comments for proposed revisions are welcome and should be submitted to: Senior Technical Director, Operations

16、 National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 At the time this standard was approved, the Conduit Fittings Section was composed of the following members: Adalet, a Division of Scott Fetzer Cleveland, OH AFC Cable Systems, Inc., a part of Atk

17、ore International New Bedford, MA Appleton Group Rosemont, IL Arlington Industries, Inc. Scranton, PA Bridgeport Fittings, Inc. Bridgeport, CT Calpipe Industries, Inc. Downey, CA Crouse-Hinds by Eaton Syracuse, NY Eatons B-Line Business Highland, IL ERICO Solon, OH Hubbell Incorporated Shelton, CT I

18、PEX USA LLC Mississauga, ON, Canada Legrand/Pass attachment first to the cable is the preferred method. A secure attachment to a box or enclosure can be made when the locknut is hand tightened and then further tightened turn using an appropriate tool. When securing the locknut, avoid excessive press

19、ure when gripping the body of the fitting. Assemble fittings supplied without locknuts to the cable and the box according to the manufacturers installation instructions. NOTELocknuts are not to be relied on to penetrate nonconductive coatings on enclosures. Such coatings are to be removed in the loc

20、knut area prior to raceway assembly to assure that a continuous ground path is achieved. 1.5.2 Attachment to Threaded Entries Armored Cable connectors having external threads may be installed into the threaded entries provided in certain boxes, enclosures, and conduit bodies. The external threads of

21、 AC fittings conforming to ANSI/NEMA FB 1 have straight threads (NPS). Threaded openings where these fittings may be installed will have tapered (NPT) or straight (NPS) threads varying in depth and number of threads. Care must be taken to ensure that at least 3 threads of the connector are fully eng

22、aged with the threads of the conduit entry when wrench tightened. 1.5.3 Support NEC Article 320 requires securement of armored cables at intervals not to exceed 1.4 m (4 ft) and within 300 mm (12 in.) of each box (note exceptions in Article 320). Securement in this manner prior to assembly to a box

23、or enclosure ensures that minimum strain will be placed on the cable-to-fitting and fitting-to-box connection during assembly and throughout the lifetime of the installation. Armored Cable shall be NEMA FB 2.20-2014 Page 6 2014 National Electrical Manufacturers Association supported at least at the

24、frequency required by the NEC, using raceway supports intended for the purpose, secured by hardware acceptable to the authority having jurisdiction. A variety of straps, clamps, staples, and hangers are available, specifically intended to secure AC and similar raceways (see Figure 1-6). These suppor

25、ts shall be installed only on cable of the trade size indicated on the support or its smallest unit shipping container. The variability of mounting surfaces, expected loads, and application environments will determine the appropriate support options and securement hardware. Design specifications usu

26、ally calculate requirements based on maximum spacing intervals given in the NEC. Use of closer support intervals than those required in the NEC is an acceptable option to heavier supports and mounting hardware in some applications. Armored Cable fittings and typical support hardware are not designed

27、 to perform the function of conductor support in long vertical installations of large-size Armored Cable (NEC Section 300.19). Often, bends are designed in such long vertical runs to relieve the strain on the conductor terminations. Consult the AC manufacturer for alternative solutions. 1.6 VERIFICA

28、TION OF INSTALLATION Loosening of raceway components is sometimes encountered during the construction process. Once the raceway is fully installed and supported, all fittings and locknuts should be re-examined for secureness. A continuity test should be performed at each connection over the entire l

29、ength of the raceway as a final means of inspection for secureness of all joints. NEMA FB 2.20-2014 Page 7 2014 National Electrical Manufacturers Association AC Single ScrewClamp Connector AC Squeeze Connector AC Connector (Without Locknut) AC Duplex Connector (Without Locknut) Twin Screw Type 90 An

30、gle Connector Figure 1-1 Typical Designs of AC Fittings, Clamp-type Screw Boss NEMA FB 2.20-2014 Page 8 2014 National Electrical Manufacturers Association Direct-bearing Radialtype Tangential Type Figure 1-2 Typical Design of AC Fitting, Screw-type Figure 1-3 Typical Integral Box Clamp for AC NEMA F

31、B 2.20-2014 Page 9 2014 National Electrical Manufacturers Association Correct Seating Incorrect Seating (Cut End Squared) (Cut End Not Properly Squared) Figure 1-4 Cut Ends of Armored Cable Incorrect Seating Correct Seating Figure 1-5 Armored Cable Securement Clamp NEMA FB 2.20-2014 Page 10 2014 Nat

32、ional Electrical Manufacturers Association Figure 1-6 Typical Armored Cable Supports NEMA FB 2.20-2014 Page 11 2014 National Electrical Manufacturers Association Section 2 FITTINGS FOR USE WITH FLEXIBLE METAL CONDUIT (TYPE FMC) Flexible Metal Conduit (FMC) is permitted for use in exposed and conceal

33、ed work for virtually all types of electrical systems and for branch circuits and feeders, where not subject to physical damage. FMC is permitted for use only in dry locations. Flexible Metal Conduit smaller than (16) trade size is not permitted, with the exception of 3/8 (12), which is allowed for

34、specific applications. For a detailed description of the permitted uses of FMC, refer to National Electrical Code (NEC) Article 348. NEC Section 250.118 allows Flexible Metal Conduit to serve as the equipment grounding conductor to ground metal boxes, enclosures, and similar components of the electr

35、ical system to a single grounding point. Particular attention should be paid to the conditions of use in this section. The requirements for listed FMC are found in UL 1, Flexible Metal Conduit. 2.1 FITTING SELECTION NEC Section 300.15 requires that “fittings and connectors shall be used only with th

36、e specific wiring methods for which they are designed and listed.” Often, fittings that are listed for use with Flexible Metal Conduit are also listed for use with Armored Cable (Type AC) and/or Metal-Clad Cable (Type MC). Consult the manufacturers instructions, labels, and literature to determine t

37、he specific wiring methods for which the fitting is intended and “listed.” Refer to tables 2-1 and 2-2 for guidance in identifying the “listed” uses of such fittings. FMC fittings are referred to by the nominal trade size of the conduit for which they are designed, typically (16) through 4 (103). Me

38、tric designators have been introduced, which correspond to these traditional trade sizes. Table 1-1 provides a cross-reference of traditional trade sizes to these metric designators. Flexible Metal Conduit fittings are available in a variety of materials, including steel, malleable iron, aluminum, a

39、nd zinc. Selection of the material type of a fitting is a matter of design consideration or personal preference, since all listed fittings conform to the same minimum performance criteria. UL 514B, Conduit, Tubing and Cable Fittings, contains the requirements for listed flexible metal conduit fittin

40、gs. ANSI/NEMA FB 1, Fittings, Cast Metal Boxes, and Conduit Bodies for Conduit, Electrical Metallic Tubing and Cable, contains manufacturing standards for FMC fittings. Four general categories describe the means by which FMC fittings attach to the conduit to ensure a sound mechanical and electrical

41、connection. Clamp-type connectors (Figure 2-1) are secured to the outside of the conduit. Direct-bearing Screwtype (Figure 2-2), and screw-in type connectors and couplings (Figure 2-3) thread inside the conduit. All connectors employ a locknut or an integral feature as a means for securement and bon

42、ding to an enclosure. Outlet and switch boxes can also be provided with integral clamps for use with flexible metal conduit (see Figure 2-4). Transition couplings enable a Flexible Metal Conduit to be coupled to RMC, IMC, or EMT. Fittings may be listed for use with any or all of the following types

43、of FMC: NEMA FB 2.20-2014 Page 12 2014 National Electrical Manufacturers Association Table 2-1 Types of Listed Flexible Metal Conduit Fittings Original FMC Reduced-wall FMC Extra Reduced Wall FMC Steel (FEFMC) Steel (FERWFMC) Steel (FEXRWFMC) Aluminum (ALFMC) Aluminum (ALRWFMC) Aluminum (ALXRWFMC) 2

44、2 REQUIRED MARKING UL 514B marking requirements provide the installer and the electrical inspector with basic information as to the specific wiring methods for which the fitting has been found acceptable and listed. A summary of those markings for fittings listed for use with Flexible Metal Conduit

45、 is provided in Table 2-2. Table 2-2 Required Markings for Flexible Metal Conduits Condition of Use or Installation Carton Marking* For use with Flexible Metal Conduit (all types) FMC For use with steel (FE) or aluminum (AL) FMC only FEFMC or STEEL FMC ALFMC or ALUM FMC or ALUMINUM FMC For use with

46、reduced-wall FMC only (steel and aluminum) RWFMC For use with reduced-wall steel (FE) or aluminum (AL) FMC only FE RWFMC or STEEL RWFMC AL RWFMC or ALUM RWFMC or ALUMINUM RWFMC For use with Extra Reduced Wall FMC only (steel and aluminum) XRWFMC For use with Extra Reduced Wall steel (FE) or aluminum

47、 (AL) FMC only FE XRWFMC or STEEL XRWFMC AL XRWFMC or ALUM XRWFMX or ALUMINUM XRWFMC *The carton marking may be prefixed by “Suitable for” or “For” or may use the word “only,” as desired or appropriate. Flexible Metal Conduit fittings, especially in the smaller trade sizes, might not be suited to ma

48、rking that conforms to UL 514B requirements for permanence and legibility. In such cases, these markings are permitted to be displayed on the products smallest unit shipping container or installation instructions. Clamps or connectors furnished as part of an outlet box in accordance with UL 514A, Me

49、tallic Outlet Boxes, or UL 514C, Nonmetallic Outlet Boxes, are marked on the clamp or connector to indicate the application for which they are intended. Example: “F” For Flexible Metal Conduit NEMA FB 2.20-2014 Page 13 2014 National Electrical Manufacturers Association 2.3 GROUNDING As previously stated, NEC Article 250 permits Flexible Metal Conduit to serve as the equipment grounding conductor to ground metal boxes, enclosures, and similar components of the electrical system to a single grounding point. All listed fitti