1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA PRP 1-2014Guidelines for Conduit-in-CasingConstructionNEMA Publication PRP 1-2014 Guidelines for Conduit-in-Casing Construction Published by National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Ros
2、slyn, Virginia 22209 www.nema.org 2014 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 Ameri
3、can copyright conventions. 2014 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by a consensus among persons engaged in its development at the time it was approved. Consensus does not necessarily mean there was
4、unanimous agreement among every person participating in the development process. The National Electrical Manufacturers Association (NEMA) standards and guideline publications, of which the document herein is one, are developed through a voluntary standards development process. This process brings to
5、gether volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. Although NEMA administers the process and establishes rules to promote fairness in the development of consensus, it does not write the documents, nor does it independently test, eva
6、luate, 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 nature, whether special, indirect, consequential, or compensat
7、ory, 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 information published herein, and disclaims and makes no warranty that the in
8、formation in this document will fulfill any particular purpose(s) or need(s). NEMA does not undertake to guarantee the performance of any individual manufacturers or sellers products or services by virtue of this standard or guide. In publishing and making this document available, NEMA is not undert
9、aking 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 or her own independent judgment or, as appropriate, seek the advice of a co
10、mpetent professional in determining the exercise of reasonable care in any given circumstance. Information 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 publ
11、ication. 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. Any certification or other statement of compliance with any health- or safe
12、ty-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. NEMA PRP 1-2014 Page i 2014 National Electrical Manufacturers Association FOREWORD The purpose of these guidelines is to describe the benefits, types
13、 and sizes, requirements, procedures, and recommended practices for installing conduit-in-casing construction. These guidelines are in no way intended to assume or replace any responsibilities of engineers, customer representatives, owners, or other persons in establishing engineering design practic
14、es and procedures best suited to individual job conditions. The NEMA Polymer Raceway Products Section, through its members, works closely with the American Society for Testing and Materials, appropriate government agencies, and other organizations in the periodic review and revision of its standards
15、 for any changes necessary to keep them up to date with advancing technology. Proposed or recommended revisions should be submitted to: Vice President, Industry Operations National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 These guidelines were de
16、veloped and approved by the NEMA Polymer Raceway Section. At the time of approval, the Polymer Raceway Section consisted of the following members: Anamet Electrical, Inc.http:/ Mattoon, IL AFC Cable Systems, a part of Atkore Internationalwww. New Bedford, MA Allied Tube and Conduit, a part of Atkore
17、 IHarvey, IL Champion Fiberglass, ISpring, TX FRE Composites 2005 ISt. Andre-dArgenteuil, PQ, Cana da Hubbell IShelton, CT IPEX Management IMississauga, ON, Canada Legrand North Americawww.legrand.usWest Hartford, CT Panduit CTinley Park, IL Royal Building PShelbyTownship, MI Southern Pipe, Inc.www.
18、southern-New London, NC Thomas 2) Bore under the surface obstruction connecting the excavated pits and install a steel casing; 3) Place conduits in the steel casing; 4) Inject grout into the area between the conduits and steel casing; 5) Allow the grout to cure; 6) Pull power and/or communication ca
19、bles through the conduits. The steel casing is usually pushed into place with hydraulic jacks, while the earth ahead of the casing is removed with special boring machines or by hand. WHY USE CONDUIT-IN-CASING CONSTRUCTION? Organization: Conduit-in-Casing construction keeps the conduits organized wit
20、hin the steel casing. The advantage of this method is the precise placement of the casing within the earth. Such precision helps avoid existing underground pipes, cables, and obstructions. The organization also keeps to a minimum underground clutter that might hinder future construction projects. Th
21、e casing is easily located and avoided by those doing future underground work. Protection: Conduit-in-casing is the obvious choice when maximum cable protection is a priority. The casing protects mission-critical cables, such as airport cables, from being severed by a natural disaster or constructio
22、n accident. Longevity: Conduit-in-casing construction provides the ultimate in longevity. Further, it is usually possible to replace cables by simply pulling out the old cables and pulling in new ones. CASING TYPES AND SIZES The most common methods used for conduit-in-casing installations use steel
23、casings. Typical steel casing sizes are shown in Table 1. Steel casings above 12 in. (304.8 mm) in diameter should always be specified by outside diameter (OD) and wall thickness. Unless there is a specific reason to the contrary, casings between 14 and 48 in. (355.6 and 1219.2 mm) should have one o
24、f the ODs shown in Table 1. Selection of casing ODs that do not conform to this table might require specialized boring equipment, resulting in higher installation costs. Casing wall thicknesses that do not conform to Table 1 are often used and usually do not pose installation problems. NEMA PRP 1-20
25、14 Page 3 2014 National Electrical Manufacturers Association Table 1 Common Steel Casings Used for Conduit-in-Casing Installations Casing OD Casing Wall Thickness Nominal Actual Under Highway Under Railroad inches mm inches mm inches mm inches mm 12 304.80 12.75 323.85 0.188 4.78 0.250 6.35 12 304.8
26、0 12.75 323.85 0.250 6.35 - - - - 14 355.60 0.188 4.78 0.250 6.35 - - 14 355.60 0.250 6.35 0.281 7.14 - - 16 406.40 0.188 4.78 0.250 6.35 - - 16 406.40 0.250 6.35 0.281 7.14 - - 18 457.20 0.250 6.35 0.312 7.92 - - 20 508.00 0.250 6.35 0.344 8.74 - - 20 508.00 - - 0.375 9.53 - - 24 609.60 0.250 6.35
27、0.375 9.53 - - 30 762.00 0.312 7.92 0.375 9.53 - - 30 762.00 0.375 9.53 0.469 11.91 - - 36 914.40 0.375 9.53 0.500 12.70 - - 36 914.40 0.500 12.70 0.531 13.49 - - 42 1066.80 0.500 12.70 0.625 15.88 - - 42 1066.80 0.750 19.05 - - - - 48 1219.20 0.500 12.70 0.688 17.48 - - 48 1219.20 0.750 19.05 - - S
28、ince wall thickness requirements vary with each location, it is important to consider soil conditions and to obtain casing approval from airport, roadway, or waterway authorities. CONDUIT NORMALLY USED Typically, the conduits used within steel casing are EPC-40 (Schedule 40) PVC per NEMA TC 2, EPC-8
29、0 (Schedule 80) PVC per NEMA TC 2, DB120 PVC conduit per NEMA TC 6 hot sand can cause the conduit to deform or collapse. NEMA PRP 1-2014 Page 7 2014 National Electrical Manufacturers Association TYPICAL BORE SPACER CROSS-SECTIONS Figures 9 and10 illustrate typical conduit-in-casing installations. Fi
30、gure 9 Duct Bank Being Installed in a Steel Casing with a Pull Plate and Winch Line Figure 10 Cross-section of a Typical Conduit-in-Casing Installation NEMA PRP 1-2014 Page 8 2014 National Electrical Manufacturers Association GROUT INJECTION TECHNIQUES There are a number of grout injection technique
31、s and variations. Figures 11-13 illustrate a few of these techniques. Figure 11 Single End Grout Injection with Bulk Heads Figure 12 Single End Extractable Grout Injection Pipe Technique NEMA PRP 1-2014 Page 9 2014 National Electrical Manufacturers Association Figure 13 Stationary Sacrificial Grout
32、Injection Pipe Technique OTHER METHODS AND PRACTICES The foregoing is a general overview of the common conduit-in-casing practice that uses a straight steel casing and nonmetallic conduits. Other methods of installing power and communication duct banks under surface obstructions that are beyond the
33、scope of this bulletin include, but are not limited to, the following: a) HDPE casing containing a nonmetallic duct bank that is pulled into a directionally drilled hole; b) Casingless duct bank that uses nonmetallic conduits, bore spacers, and bands that is pulled into a directionally drilled hole;
34、 c) Reinforced thermosetting resin fiberglass casing containing nonmetallic conduits that is placed in a dredged trench and backfilled with marine grade concrete; d) Casingless duct bank that uses bore spacers and bands that is pulled into a dredged trench and is then backfilled with marine grade co
35、ncrete; e) Concrete pipe casing and nonmetallic conduit; f) Centrifugally Cast Fiberglass Reinforced Polymer Mortar (CCFRPM) pipe and nonmetallic conduit. NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION 1300 NORTH 17TH STREET, SUITE 900 ROSSLYN. VA 22209www.NEMA.orgTO ORDER ADDITIONAL NEMA STANDARDS VISITWWW.GLOBAL.IHS.COM OR CALL 1-800-854-7179/1-303-397-79565612_0514TB
