1、 NEMA TCB 2-2012 NEMA Guidelines for the Selection and Installation of Underground Nonmetallic Raceways NEMA TCB 2-2012 NEMA Guidelines for the Selection and Installation of Underground Nonmetallic Raceways Published by: National Electrical Manufacturers Association 1300 North 17th Street, Suite 900
2、 Rosslyn, Virginia 22209 www.nema.org 2013 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 A
3、merican copyright conventions. TCB 2-2012 Page ii 2013 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 nece
4、ssarily mean there was 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.
5、 This process brings together 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
6、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 nature, whether special, indirect, cons
7、equential, 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 information published herein, and disclaims and makes
8、no warranty that the information 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 availa
9、ble, 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 or her own independent judgment or, as appropriate,
10、seek the advice of a competent 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 n
11、ot 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. Any certification or other statement of compliance w
12、ith any health- or safety-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. TCB 2-2012 Page iii 2013 National Electrical Manufacturers Association FOREWORD This guideline is intended to provide assistan
13、ce as a guide to obtain the most appropriate and satisfactory installation of rigid nonmetallic conduit (RNC) or raceway systems. This guideline is in no way intended to assume or replace any responsibilities of engineers, customer representatives, owners, or other persons in establishing engineerin
14、g design practices and procedures best suited to individual job conditions. NEMA Polymer Raceway Products Section Anamet Electrical, Inc. Mattoon, IL AFC Cable Systems, a part of Atkore International New Bedford, MA Allied Tube and Conduit, a part of Atkore International Harvey, IL Champion Fibergla
15、ss, Inc. Spring, TX FRE Composites St. Andr-dArgenteuil, PQ, Canada Hubbell Incorporated Shelton, CT IPEX Electrical Inc. Mississauga, ON, Canada Legrand North America West Hartford, CT Panduit Corporation Tinley Park, IL Royal Pipe Systems Shelby Township, MI Southern Pipe, Inc. New London, NC Thom
16、as details on storage, handling, and installation are covered in NEMA TCB-3. Although not specifically mentioned in this guideline, variations of the products discussed may occasionally be specified. Users should follow installation recommendations of the manufacturer. NOMENCLATURE Abbreviations for
17、 nonmetallic materials referenced in this guideline include the following: HDPE High Density Polyethylene PE Polyethylene PVC Polyvinyl Chloride RTRC Reinforced Thermosetting Resin Conduit (fiberglass) Abbreviations for burial type include: DB Direct burial refers to duct buried without concrete enc
18、asement EB Encased burial refers to duct buried with concrete encasement Abbreviations for stiffness include: DS Duct stiffness PS Pipe stiffness Abbreviations for conduit type include: EPC 40 PVC conduit (Schedule 40) EPC 80 Extra heavy wall PVC conduit (Schedule 80) EPEC Smooth wall coilable high
19、density polyethylene conduit RNC Rigid nonmetallic conduit Abbreviations for wall type include: HW Heavy wall refers to HW RTRC SW Standard wall refers to SW RTRC XW Extra heavy wall refers to XW RTRC STANDARDS AND GUIDELINES REFERENCES ASTM D 2412 Standard Test Method for Determination of External
20、Loading Characteristics of Plastic Pipe by Parallel-Plate Loading ASTM D 2564 Standard Specification for Solvent Cements for Poly(Vinyl Chloride) (PVC) Plastic Piping Systems ASTM D 2657 Standard Practice for Heat Fusion Joining of Polyolefin Pipe and Fittings ASTM D 2855 Standard Practice for Makin
21、g Solvent-Cemented Joints with Poly(Vinyl Chloride) (PVC) Pipe and Fittings TCB 2-2012 Page 2 2013 National Electrical Manufacturers Association ASTM F 402 Standard Practice for Safe Handling of Solvent Cements, Primers, and Cleaners Used for Joining Thermoplastic Pipe and Fittings ASTM F 656 Standa
22、rd Specification for Primers for Use in Solvent Cement Joints of Poly(Vinyl Chloride) (PVC) Plastic Pipe and Fittings NEMA TC 2 Electrical Polyvinyl Chloride (PVC) Conduit NEMA TC 6 EPC-40 meeting NEMA TC 2; EPC-80 meeting NEMA TC 2; EPEC meeting NEMA TC 7; RTRC SW and HW. DB PVC duct, RTRC, EPC-40,
23、 EPC-80 and EPEC may also be encased in concrete (either in trenches or in casings or borings) for extra heavy or high dynamic load applications such as under railroad beds (see Appendix B). PIPE STIFFNESS Pipe stiffness (PS), also known as duct stiffness (DS), is a useful test value for evaluating
24、the load bearing and deflection characteristics of the raceway. Pipe stiffness is dependent upon two factors: the modulus of elasticity of the raceway material, and the moment of inertia of the raceway (which is a function of the raceway diameter and wall thickness). In the design of each raceway sy
25、stem, consideration should be given to pipe stiffness requirements to withstand the specific application loadings. ASTM D 2412 is the generally accepted test method for determining pipe stiffness. Appendix X1 of D 2412 gives a method of using pipe stiffness to calculate approximate deflections under
26、 earth loads. Pipe stiffness values are determined at a specified inside diameter (ID) deflection of 5%. Values are expressed in pounds of force per inch of raceway length per inch of deflection (kPa). PS = F/y Where: PS = pipe stiffness in lbs./inch/inch (kPa) F = load in pounds(kg) per inch(mm) of
27、 raceway length that deflects the ID 5% y = change in ID in inches (mm) due to the applied load F Minimum pipe stiffness requirements for EB PVC duct, DB PVC duct, SW RTRC, and HW RTRC are specified in the applicable NEMA standards. TCB 2-2012 Page 4 2013 National Electrical Manufacturers Associatio
28、n Handling and Storage of Conduit and Duct HANDLING Generally, raceways are shipped on reels or in self-supporting framed units designed for mechanical unloading. Abusive handling should be avoided. Units should not be dropped from truck or beds. Raceways may also be shipped in vans, either loose or
29、 in bundles. Care should be taken to avoid damage during shipping. Prolonged storage of shipments of raceways in closed vans should be avoided, since excessive weight and elevated temperature may cause ovality on the bottom raceways. Care should be exercised when handling thermoplastic raceways in t
30、emperatures below 32 F (0 C), and when handling RTRC in temperatures below -40 F (-40 C). STORAGE Recommendations for storage of raceways are given below. Additional recommendations from the manufacturer should also be followed. Framed Units Framed units should be stored on a level surface. The wood
31、 frames should line up, one on top of another, so that the load is on the wood frames rather than on the raceway. Standing height of stacked units should be limited to 12 feet (3.6 m). TCB 2-2012 Page 5 2013 National Electrical Manufacturers Association Coils and Reels The storage area should be of
32、sufficient size to accommodate the raceway and components, to allow room for handling equipment to get around them and to have a relatively smooth level surface free of stones, debris, and other material that could damage the raceway or components, or interfere with handling. Bulk Storage Loose race
33、ways should be stacked in a parallel manner. To avoid excessive ovality on the bottom row, the stacking height should be limited to four feet (1.2 m) for EB duct and five feet (1.5 m) for DB duct. The bottom row of raceway should be laid on as level a surface as possible. Supports should not be plac
34、ed under the raceway, as excessive deflection and sagging could result. TCB 2-2012 Page 6 2013 National Electrical Manufacturers Association Elbows and Sweeps Elbows and sweeps can be stored outdoors on flat ground. The manufacturer should be consulted for other preventive storage procedures. Fittin
35、gs, Spacers, and Accessories When stored outdoors, fittings, spacers, and accessories in cartons should be under cover to protect cartons from the elements. Cleaners, Primers, Cements, and Adhesives All cleaners, primers, cements, and adhesives should be stored in a cool place except when actually i
36、n use at the job site. They should not be stored in freezing areas as this can cause premature gelation and loss of the cements. Some products have a limited shelf life when not stored in hermetically sealed containers. The product manufacturer should be consulted for specific recommendations on sto
37、rage conditions and shelf life. In hermetically sealed containers, the normal shelf life of these products is approximately one to two years. Note: Some products are flammable. Fumes can be harmful if adequate ventilation is not provided. Inventories It is recommended that inventories be rotatedfirs
38、t in, first outto minimize possible product deterioration from excessive storage time. HANDLING ON THE JOBSITE Conduit and Duct Abusive handling should be avoided at all times. Care should be exercised when handling thermoplastic raceways in temperatures below 32 F (0 C), and when handling RTRC in t
39、emperatures below -40 F (-40 C). Coils and Reels Use of appropriate unloading and handling equipment of adequate capacity is required to unload the truck. Safe handling and operating procedures are required to be followed. Coils or reels are not to be rolled or pushed off the truck. During cold weat
40、her, care should be taken not to drop the raceway and to keep handling equipment and other objects from hitting the raceway. Solvent Products The handling of solvent products should be in accordance with ASTM F 402 Standard Recommended Practice for Safe Handling of Solvent Cements Used for Joining T
41、hermoplastic Pipe and Fittings. Inventories It is recommended that inventories be rotated first in, first out to minimize possible product deterioration from excessive storage time. TCB 2-2012 Page 7 2013 National Electrical Manufacturers Association Installation of Conduit and Duct PROPER INSTALLAT
42、ION A raceway system is considered to be properly installed if the inside diameter of each raceway is adequate to allow free passage of the specified deflection mandrel. To limit deflection, special attention should be paid to trench bedding, raceway separation, distance between supports, joining of
43、 raceways, type of backfill material, and amount of compaction. TRENCH EXCAVATION All federal, state, and local regulations should be followed, including those pertaining to: Rights of way; Permits; Combined trenches; Excavation of open trenches; Shoring; Minimum cover over raceways; Safety. Routing
44、 of the raceway should be coordinated with all utility companies who may have underground lines in the area of the proposed trenching layout. TCB 2-2012 Page 8 2013 National Electrical Manufacturers Association The trench dimensions are determined as follows: The depth is determined by the height of
45、 the duct bank, plus the minimum required cover over the bank; The width of the trench is determined by the width of the duct bank to be installed plus a minimum three-inch (76-mm) space on each side to adequately place and compact the backfill material. If shoring is required, additional trench wid
46、th may be necessary. Trench Wall Where unstable soil conditions are encountered in the trench wall, these conditions should be stabilized before laying the raceway. The design engineer is responsible for providing methods to control such conditions. Well points or under drains may be required to con
47、trol excessive groundwater conditions. Where required by regulations or by soil conditions, the trench walls should be adequately shored. Care should be taken that the raceway installation is not disturbed by removal of shoring materials. Trench Bottom The trench bottom should be smooth and free of
48、any debris that may be detrimental to the raceway or impede the positioning of spacers or supports. Where the trench bottom is rocky, a four-inch (103-mm) layer of compactable bedding material is recommended. In direct burial applications, bedding is to be uniformly graded to provide continuous supp
49、ort. Under no circumstances should blocking or mounding be used to raise the raceway to grade. An unstable trench bottom, where encountered, is to be stabilized before laying raceway. Usually, this can be accomplished by over-excavating and providing a bedding of crushed stone or gravel to provide a stable base. This material should be suitably graded to act as an impervious mat through which the unstable soil does not penetrate. Maximum particle size of the bedding material should be 1 inch (25 mm). To aid
