1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA TCB 4-2016Guidelines for the Selection and Installation of Smooth-Wall Coilable High-Density Polyethylene (HDPE) ConduitNEMA TCB 4-2016 Guidelines for the Selection and Installation of Smooth-Wall Coilable High-Density Polye
2、thylene (HDPE) Conduit Reprinted with permission from Dura-line Published by National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2016 National Electrical Manufacturers Association. All rights including translation into other languages,
3、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. 2016 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was co
4、nsidered technically sound 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 Electr
5、ical Manufacturers Association (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
6、the topic covered by this publication. 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
7、 of any judgments contained in its 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, ap
8、plication, 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 information in this document will fulfill any of your particular purpose
9、s 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 guide. In publishing and making this document available, NEMA is not undertaking to render professional or other services for or on behalf of
10、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 competent professional in determining the exercise of reasonable care
11、 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 wish to consult for additional views or information not covered by this publication. NEMA has no power, nor does it undertake to police or enf
12、orce 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 safety-related information in this document shall not be attributable
13、to NEMA and is solely the responsibility of the certifier or maker of the statement. 2016 National Electrical Manufacturers Association Foreword This guideline is intended to provide assistance with obtaining the most appropriate and satisfactory installation of HDPE conduit or raceway systems. It i
14、s in no way intended to assume or replace any responsibilities of engineers, customer representatives, owners, or other persons in establishing engineering design practices and procedures best suited to individual job conditions. During the preparation phase of this document, the following were acti
15、ve participants: Randy KummerSouthwire Company Andrew NauseIPEX Management, Inc. Lance MacNevinPlastics Pipe Institute NEMA TCB 4 was approved by the NEMA Polymer Raceway Products Section. Approval does not necessarily imply that all members of the section voted for its approval. At the time of appr
16、oval, the section consisted of the following members: Anamet Electrical, IMattoon, IL AFC Cable Systems, Inc., a part of Atkore INew Bedford, MA Allied Tube and Conduit, a part of Atkore IHarvey, IL Champion Fiberglass, ISpring, TX Electri-Flex CRoselle, IL FRE CSt. Andre-dArgenteuil, PQ, Canada Hub
17、bell IShelton, CT IPEX USA LLChttp:/ ON, Canada Legrand, North Americawww.legrand.usWest Hartford, CT Panduit CTinley Park, IL Royal Building PShelby Township, MI Southern Pipe, Inc.www.southern-New London, NC Southwire CCarrollton, GA Thomas b. The width of the trench is determined by the width of
18、the duct bank to be installed plus a minimum 3 in. (76 mm) space on each side to adequately place and compact the backfill material. If shoring is required, additional trench width may be necessary. Trench Wall Where unstable soil conditions are encountered in the trench wall, these conditions shoul
19、d be stabilized before laying the raceway. The design engineer is responsible for providing methods to control such conditions. Well points or underdrains may be required to control excessive groundwater conditions. Where required by regulations or if soil conditions dictate, the trench walls should
20、 be adequately shored. Take care that the raceway installation is not disturbed by removal of shoring materials. OSHA trenching and excavation safety requirements in 29 CFR 1926.651 and 1926.652, or comparable OSHA-approved state plan requirements, must be followed. Trench Bottom The trench bottom s
21、hould be smooth and free of any debris that may be detrimental to the raceway or impede the positioning of spacers or supports. Where the trench bottom is rocky, a 4 in. (103 mm) layer of compactable bedding material is recommended. In direct burial applications, bedding is to be uniformly graded to
22、 provide continuous support. 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 ston
23、e 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 in. (25 mm). To aid in placement around small-diameter raceway and to prevent damage
24、 to the raceway wall, a smaller maximum size may be specified. Take care to prevent rocks, hard lumps, frozen clods, organic matter, and other foreign material from falling into the trench. Conduit Separation Raceway Supports For encased burial (EB), raceway separation can be achieved by use of spac
25、ers. There are many different configurations of commercially available spacers; see Figure 1 for examples. For direct burial (DB), supports need to meet the conditions specified by the design engineer. Conduit and duct spacers are not designed for DB applications. The use of spacers in a DB applicat
26、ion may result in backfill voids and excessive deflection points on the raceways. Figure 1 Examples of Spacers Power Duct Banks In power duct banks, individual raceways should be separated from one another. The reasons for this are as follows: a. To provide adequate dissipation of the normal build-u
27、p of heat from cables within the raceway b. To provide void space to allow the encasement material to fully surround each raceway c. To physically separate raceways in the event of a cable fault Communication Duct Banks Since there is no appreciable build-up of heat or risk of a cable fault in commu
28、nication duct banks, separation only allows the encasement material to fully surround each raceway. Combined Power and Communication Duct Banks Many specifications require 3 in. (76 mm) or more of separation between power and communication raceways. Since spacer manufacturers generally do not manufa
29、cture spacers with a separation of greater than 3 in. (76 mm), dummy spacers can be inserted between the power and communication raceways to provide acceptable separation. Custom spacers for separations of greater than 3 in. (76 mm) may be available. Considerations for Specifiers Duct bank designers
30、 should specify raceway separations around commercially available spacers. Frequently the duct bank designer specifies center-to-center dimensions between raceways, leaving the contractor with the responsibility of calculating the separation dimensions. For power and communication raceways, specifie
31、rs should keep in mind that stock spacers are available to provide separations of 1 in. (25 mm), 1 in. (38 mm), 2 in. (51 mm), and 3 in. (76 mm). Custom spacers for other separations may be available. Consult NEMA member spacer manufacturers. Joining of Raceway General An integral part of any PE con
32、duit system is the type and quality of joining method used. PE conduit can be joined by a variety of thermal and mechanical methods. Proper engineering design of a system will consider the type and effectiveness of these joining techniques. Joint Performance Considerations Performance considerations
33、 that affect the systems reliability well beyond initial installation include: a. Pull-out resistance due to thermal contraction and expansion must be considered both at installation and over time. During installation, “blow-in” cable installations exert an outward force at joints. “Pull-in” cable i
34、nstallations exert an inward force, but to a lesser extent than a blow-in installation. b. Pressure leak rates for “blow-in” installations at pressures of 125150 psig must be considered in terms of how much leakage can be tolerated without reducing the distance the cable can consistently be moved th
35、rough the PE conduit. c. Infiltration leakage, when water and/or silt entering the PE conduit over time can create obstacles for cable installation and repair or cause water freeze compression of fiber optic cables. d. Corrosion resistance is important, since PE conduit systems are often buried in s
36、oils exposed to and containing alkali, fertilizers, ice-thawing chemicals, insecticides, herbicides, and acids. e. Cold temperature brittleness resistance is required to avoid problems with installation and long-term performance in colder climates. Joining methods PE-to-PE joints may be made using h
37、eat fusion, electrofusion, or mechanical fittings. Mechanical couplings are often preferred over butt fusion joints because of the potential for the internal bead of a butt fusion joint to interfere with cable installation. PE conduit may be joined to other materials in junction boxes or other hardw
38、are utilized by communication and electrical industries by using mechanical fittings, flanges, or other types of transition fittings. The user may choose from many available types and styles of joining methods, each having its own particular advantages and limitations for any joining situation. For
39、any fitting style being considered, consult the fitting manufacturer for available sizes, as well as any performance limitations and written instructions for use. Mechanical Fittings PE conduit can be joined by a variety of styles of mechanical fittings, each with its own particular advantages and l
40、imitations in any given application. This section will not address these advantages or limitations but will only offer general descriptions of many of these fitting types and how they might be utilized. ASTM F2176, “Standard Specification for Mechanical Couplings Used on Polyethylene Conduit, Duct a
41、nd Innerduct” establishes performance requirements for material, workmanship, and testing of 2 in. (51 mm) and smaller mechanical fittings for PE conduit. Barbed Mechanical Fittings Barbed fittings are available in various materials and configurations for joining PE conduit sizes 2 in. (51 mm) and s
42、maller. Installation involves pressing the fitting over ends of the PE conduit to be joined using a special tool. The inside of these fittings contains sharp, inward-facing barbs that allow the PE conduit to be pressed in, yet dig into the PE conduit and resist removal when pulled. Threaded Mechanic
43、al Fittings Threaded mechanical fittings are available in various materials and configurations for PE conduit sizes 2 in. (51 mm) and smaller. Some are designed with sealing capabilities; others are not. Internal thread designs of these fittings are typically tapered similar to pipe threads, with a
44、left-hand thread on one end and a right-hand thread on the other to cut thread paths on the PE conduits outer surface. This thread design allows the operator to thread the fitting onto the ends of both PE conduit sections simultaneously. Some variations of threaded fittings may also be pressed on th
45、e PE conduit ends and used as barbed fittings. Compression Fittings Compression fittings are also available in numerous designs, some for PE conduit as large as 8 in. (203 mm) and others for only 2 in. (51 mm) and below. While compression fittings used in PE pressure piping industries such as water
46、or gas require internal stiffeners, PE conduit systems typically do not because stiffeners may create obstacles for cable being blown through the PE conduit. Heat Fusion The principle of heat fusion is to heat two surfaces to a designated temperature and fuse them together by application of a force
47、sufficient to cause the materials to flow together and mix. When fused in accordance with the manufacturers recommended procedure and allowed to cool to nearly ambient temperatures, the joint becomes as strong or stronger than the PE conduit itself in both tensile and pressure properties. More speci
48、fic information on heat fusion joining practices can be found in ASTM F2620 for hot iron methods (butt and socket fusion) and in ASTM F1290 for electrofusion. The user must precisely follow the qualified fusion procedures established by the manufacturer of the particular heat fusion and joining equipment being used. Three primary heat fusion methods used in joining PE conduit are butt, socket, and electrofusion, described as follows. Butt Fusion Joining Butt fusion joints are produced without need of special fittings, using specially
