1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA RV 3-2014Application andInstallation Guidelines for Flexible and LiquidtightFlexible Metal andNonmetallic ConduitsNEMA STANDARDS PUBLICATION RV 3-2014 Application and Installation Guidelines for Flexible and Liquidtight Flex
2、ible Metal and Nonmetallic Conduits 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 Univer
3、sal Copyright 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 soun
4、d by the 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 Associ
5、ation (NEMA) 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
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12、contents 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
13、 responsibility of the certifier or maker of the statement. NEMA RV 3-2014 Page i 2014 National Electrical Manufacturers Association Foreword These application and installation guidelines offer practical information on correct usage and industry-recommended practices for the installation of Flexible
14、 Metal Conduit (Type FMC) and Liquidtight Flexible Metal Conduit (Type LFMC) in accordance with the National Electrical Code (NEC). These guidelines have been developed by the NEMA Building Wire and Cable Group. The Groups Flexible Metal Conduit Technical Committee has committed to periodically revi
15、ewing them for any revisions necessary to address changing conditions, product listing and installation requirements, and technical progress. Comments for proposed revisions are welcome and should be submitted to: Senior Vice President, Operations National Electrical Manufacturers Association 1300 N
16、orth 17th Street, Suite 900 Rosslyn, Virginia 22209 At the time of approval, the NEMA Building Wire and Cable Groups Flexible Metal Conduit Technical Committee had the following members: AFC Cable Systems, Inc., A part of Atkore International New Bedford, MA Anamet Electrical, Inc. Mattoon, IL Elect
17、ri-Flex Company Roselle, IL Encore Wire Corporation McKinney, TX International Metal Hose Company Bellevue, OH Southwire Company Carrollton, GA NEMA RV 3-2014 Page ii 2014 National Electrical Manufacturers Association CONTENTS Page Foreword i Section 1 APPLICATION GUIDELINES FOR FLEXIBLE METAL CONDU
18、IT 1 1.1 Construction . 1 1.1.1 General . 1 1.1.2 Conduit . 1 1.2 Grounding and Bonding . 1 1.3 Equipment Grounding Conductor . 1 1.4 Codes and Standards. 1 1.4.1 National Electrical Code (NEC) 1 1.4.2 Related NEC Articles . 2 1.4.3 Underwriters Laboratories (UL) Standards and Directories . 4 Sectio
19、n 2 APPLICATION GUIDELINES FOR LIQUIDTIGHT FLEXIBLE METAL AND NONMETALLIC CONDUIT 6 2.1 Construction . 6 2.1.1 General . 6 2.1.2 Jacket Material . 6 2.1.3 Fittings 7 2.2 Grounding . 7 2.2.1 LFNC 7 2.2.2 LFMC 7 2.3 Marking . 7 2.3.1 LFNC 7 2.3.2 LFMC 7 2.4 Codes and Standards. 7 2.4.1 National Electr
20、ical Code (NEC) . 7 2.4.2 Related NEC Articles . 9 2.4.2 Underwriters Laboratories (UL) Standards and Directories . 11 Section 3 INSTALLATION GUIDELINES FOR FLEXIBLE METAL CONDUIT AND LIQUIDTIGHT FLEXIBLE METAL CONDUIT 13 3.1 Installation Considerations . 13 3.1.1 General . 13 3.1.2 Special Consider
21、ations for LFMC 13 3.1.3 Overall Conduit Length 13 3.2 Securing and Supporting FMC and LFMC . 14 3.2.1 Supported . 15 3.2.2 Unsupported . 15 3.3 Terminating Flexible Metal Conduit 15 3.3.1 Fitting Selection 15 3.3.2 Conduit Preparation and Assembly 16 3.3.3 Cutting Conduit . 16 3.3.4 Inserting Condu
22、it 16 3.3.5 Seating a Securement Clamp 17 3.3.6 Tightening Torque 17 3.3.7 Attachment to Unthreaded Entries . 17 3.3.8 Attachment to Threaded Entries 18 3.4 Terminating Liquidtight Flexible Metal Conduit 18 3.4.1 Fitting Selection 18 3.4.2 Conduit Preparation and Assembly 18 3.5 Verification of Inst
23、allation . 20 NEMA RV 3-2014 Page iii 2014 National Electrical Manufacturers Association Section 4 INSTALLATION GUIDELINES FOR LIQUIDTIGHT FLEXIBLE NONMETALLIC CONDUIT (LFNC) 21 4.1 Installation Considerations . 21 4.1.1 General . 21 4.1.2 Types 21 4.2 Securing and Supporting LFNC . 21 4.2.1 Support
24、ed . 21 4.2.2 Unsupported . 21 4.3 TERMINATING LFNC 22 4.3.1 Fitting Selection 22 4.3.2 Environmental Considerations . 23 4.3.3 Required Marking on Fittings . 23 4.3.4 Grounding . 24 4.3.5 Conduit Preparation and Fitting Assembly Technique . 24 4.3.6 Attachment to Boxes or Enclosures and Support 25
25、4.4 VERIFICATION OF INSTALLATION . 26 Annexes Annex A NEMA Engineering Bulletin No. 93: Length Limitations for FMC and LFMC . 33 Figures Figure 1 Determination of Overall Length of Conduit Installed in a Traveling Vertical Loop with Offset . 14 Figure 2 Straight Length 14 Figure 3 Typical Designs of
26、 FMC Fittings, Clamp-type 26 Figure 4 Typical Designs of FMC Fittings, Direct-bearing Screw Type 27 Figure 5 Typical Designs of FMC Fittings, Screw-in Type 27 Figure 6 Typical Designs of Liquidtight Flexible Nonmetallic Conduit Fittings . 28 Figure 7 Typical Designs of Liquidtight Flexible Metal Con
27、duit Fittings . 29 Figure 8 Flexible Metal Conduit Securement Clamp 32 Tables Table 1 Standard Assembly Torque Values for Type FMC Fittings 17 Table 2 Standard Assembly Torque Values for Type LFMC Fittings 19 Table 3 Markings for Fittings for Use with Liquidtight Flexible Nonmetallic Conduit . 23 Ta
28、ble 4 Assembly Torque Values for LFNC Fittings . 25 Table 5 Overall Conduit Length for Given Offset and Lateral Distance Trade Size 30 Table 6 Overall Conduit Length for Given Offset and Lateral Distance Trade Size 30 Table 7 Overall Conduit Length for Given Offset and Lateral Distance Trade Size 1
29、. 31 Table 8 Overall Conduit Length for Given Offset and Lateral Distance Trade Size 1 31 Table 9 Overall Length of Conduit for Given Offset and Lateral Distance Trade Size 1 32 Table 10 Overall Length of Conduit for Given Offset and Lateral Distance Trade Size 2 . 32 NEMA RV 3-2014 Page iv 2014 Nat
30、ional Electrical Manufacturers Association NEMA RV 3-2014 Page 1 2014 National Electrical Manufacturers Association Section 1 APPLICATION GUIDELINES FOR FLEXIBLE METAL CONDUIT 1.1 CONSTRUCTION 1.1.1 General Flexible Metal Conduit (Type FMC) is constructed in accordance with the National Electrical C
31、ode (NEC) and complies with the safety requirements of Underwriters Laboratories (UL) UL 1, Standard for Safety for Flexible Metal Conduit. National Electrical Code and NEC are registered trademarks of the: National Fire Protection Association, Inc. 1 Batterymarch Park Quincy, MA 02269 1.1.2 Conduit
32、 Flexible Metal Conduit (Type FMC) is constructed with an interlocked corrosion-resistant steel or aluminum strip and is manufactured in accordance with UL 1, which specifies strip thickness, splices, convolutions, interior surfaces, conduit diameters (internal and external), and the quality require
33、ments of aluminum strip and zinc-coated steel. 1.2 GROUNDING AND BONDING FMC is approved for bonding when installed in accordance with NEC articles 348 and 250 but is limited to 6-ft lengths when used for this purpose. 1.3 EQUIPMENT GROUNDING CONDUCTOR One or more equipment grounding conductors are
34、allowed but are not required. NEC Section 348.60 states, however, that an equipment grounding conductor is required when FMC is used to connect equipment where flexibility is necessary to minimize transmission of vibration from equipment or to provide flexibility for equipment that requires movement
35、 after installation. 1.4 CODES AND STANDARDS 1.4.1 National Electrical Code (NEC) Flexible Metal Conduit (FMC) is designed, manufactured, and tested for use in accordance with NEC Article 348 and UL 1. 1.4.1.1 Uses Permitted NEC Section 348.10 specifies the permitted uses of FMC in exposed and conce
36、aled locations. These permitted uses are not all-inclusive. They provide guidance only on where FMC may be used. In addition to permitted uses covered in Section 348.10, FMC is permitted for installation as follows: a) Outside branch circuits and feeders; b) Services; c) Ducts or plenums used for en
37、vironmental air; d) In other spaces used for environmental air; e) Under raised floors of computer rooms; f) Lighting whips; g) Motor leads. NEMA RV 3-2014 Page 2 2014 National Electrical Manufacturers Association These permitted uses might imply that there is no limitation on the use of FMC. Limita
38、tions are covered, however, in NEC Section 348.12, “Uses Not Permitted.” Additionally, a key provision of the NEC for permitted uses is that wiring methods are required to comply with all applicable sections of the NEC. Article 348, for example, does not impose a length limitation on FMC trade sizes
39、 and larger; however, when used in accordance with Section 430.223 for raceway connections to motor circuits over 1000 V, a 6-ft limitation is imposed. 1.4.1.2 Uses Not Permitted As with permitted uses, those uses not permitted by the NEC are not all-inclusive. The Code language is intended to provi
40、de guidance on where and how FMC may be used. NEC Section 348.12 specifies the uses of FMC that are not permitted, which are as follows: a) In wet locations; b) In hoistways, other than as permitted in 620.21(A)(1); c) In storage battery rooms; d) In any hazardous (classified) location, except as pe
41、rmitted by other articles in the Code; e) Where exposed to materials having a deterioration effect on the installed conductors, such as oil or gasoline; f) Underground or embedded in poured concrete or aggregate; g) Where subject to physical damage. The following provides additional guidance on the
42、uses of FMC: Corrosive environments and use underground: Review of the uses not permitted shows that Flexible Metal Conduit cannot be installed where corrosive environments might be present or in concrete or underground locations. For such installations, a FMC with a protective outer covering, such
43、as Liquidtight Flexible Metal Conduit with an outer nonmetallic jacket approved for the use, should be used. Where subject to physical damage: FMC must be protected from physical damage. This protection includes installing FMC at heights and locations where it will not be exposed to damage. It also
44、includes providing mechanical protection, such as from nails and screws, in accordance with Section 300.4(D) by maintaining a 1 in. (32 mm) distance from the edge of a framing member or, where the distance cannot be maintained from the edge of a framing member or a furring strip, by providing a meta
45、l plate. 1.4.2 Related NEC Articles The following NEC articles also contain provisions for use of FMC: Wiring and Protection Article 225, “Outside Branch Circuits and Feeders” 225.10 Wiring on Buildings Article 230, “Services” 230.43 Wiring Methods for 1000 Volts, Nominal, or Less Article 250, “Grou
46、nding and Bonding” 250.118 (5) Use of the Armor of FMC as Equipment Grounding Conductor Wiring Methods and Materials Article 300, “Wiring Methods” 300.22 Wiring in Ducts Not Used for Air Handling, Fabricated Ducts for Environmental Air, and Other Spaces for Environmental Air (Plenums) (B) Ducts Spec
47、ifically Fabricated for Environmental Air (C) Other Space Used for Environmental Air NEMA RV 3-2014 Page 3 2014 National Electrical Manufacturers Association Article 348, “Flexible Metal Conduit: Type FMC Article 368, “Busways” 368.56 Branches from Busways Article 374, “Cellular Metal Floor Raceways
48、” 374.11 Connection to Cabinets and Extensions from Cells Article 392, “Cable Trays” 392.10 Uses Permitted (A) Wiring Methods Equipment for General Use Article 410, “Luminaires (Lighting Fixtures), Lampholders, and Lamps” XII. Special Provisions for Electric-Discharge Lighting Systems of 1000 Volts
49、or Less 410.137 Equipment Not Integral with Luminaire (C) Wired Luminaire (Fixture) Sections Article 430, “Motors, Motor Circuits, and Controllers” XI. Over 600 Volts, Nominal 430.223 Raceway Connection to Motors XIII. “GroundingAll Voltages” 430.245 Method of Grounding (B) Separation of Junction Box from Motor Special Occupancies Article 501, “Class I Locations” 501.10 Wiring Methods (B) Class I, Division 2-(2) Flexible Connections 501.30 “Grounding and Bonding, Class I, Divisions 1 and 2” (B) Types of Grounding Conductors Article 505, “Class I,
