Rigid Aluminum Conduct

1 Section VI Related Structural Applications of Aluminum Chapter 17 Rigid Aluminum Conduct One of the earliest. and still most effective, methods of installing concealed electrical cable within the structure of a building, in the building foundations or the sub grade is the use of Rigid conduit. The many advantages Rigid conduit provides include, A very high order of mechanical and flame protection for the enclosed cables. A high order of safety to personnel who might otherwise accidentally come in contact with the ungrounded portion of the electrical system. An easy pulling, smooth, snag-free pathway for the cables through an otherwise intricate, many-turned run.

2 Pull-boxes to enable straight pulls as required. An easy means for replacing conductors or pulling in additional ones. Permanent, built-in cable runways in cast concrete structures. Elements of Conduit Design Important elements in the design of electrical conduit He related to, Adequate strength in relation to size for self-support over reasonable lengths. Smooth, round, burr-free interior. Capability of being cut and threaded readily and bent smoothly (no flattening) with normal field methods and tools. Provision and maintenance of good electrical conduc tivity through the conduit proper and across all threaded joints. Development of a compatible line of accessories, such as elbows, couplings.

3 Unions, tees, pull and junction boxes. Freedom from destructive corrosion in the working environment. Provision for expansion fittings for long lengths oper ating under widely varying temperature conditions. installation and construction requirements for electrical conduit are set by the National Electrical Code (NEC). These include Rigid Aluminum , galvanized steel, IMC (intermediate metal conduit) and nonmetallic conduit, as well as conduit fittings, conduit bodies and boxes in Aluminum , galvanized steel and PVC. Individual product lines must be manufactured to conform to the standards set forth by Underwriters Laboratories, in order to qualify for UL Labels.

4 The factors involved in NEC Rigid conduit specifications relate to installation and operating requirements. For example, the Code specifies maximum allowable fill areas for given conduit sizes. Table 17-1, abstracted from the 1987 NEC, shows the allowable fill area for each conduit trade size. * Table 17-3 gives cross-sectional areas for typical conductor sizes insulated with both thermosetting and thermoplastic materials. Table 17-4 converts these area limitations to the number of typical conductor sizes permitted in one conduit based on both thermosetting and thermoplastic insulations. Tables 17 Sa and 17-5b give dimensions of Rigid Aluminum , galvan ized steel, andIMC.

5 Table 17-6 gives comparative weights for the three types of metallic conduit. The NEC also recognizes the effect of the conduit or raceway on temperature rise of the encased conductor. In Chapter 9 of this book, Tables 9-3, 9-4, 9-5, 9-6 and 9-7 show characteristics of wires and feeders in magnetic and non-magnetic conduit or raceways. Metallic conduits can contribute a small amount ofheating due to hysteresis (if the conduit is magnetic) and eddy current losses. Of greatest importance in its effect on ampacity, however, is the number of loaded conductors in a given conduit. The tables referenced above give ampacity data for the case of not more than three loaded conductors per conduit.

6 When the number of conductors increases to from 4 to 6 the ampacity values are reduced to 80% of the tabulated value. If there are 7 to 24 conductors in the conduit, the allowable currents are to be reduced to 70% of the tabulated value. (The neutral conductors, since they only carry the unbalanced currents in normally balanced circuits, are not to be considered in determining '" Table 17~2 shows the maximum number of compact conductors allowable in conduit or tubing:. 17-1 I related strudural applications of Aluminum TABLE 17-1 Conduit-Allowable Fill Area Square Inches Conduit Trade Size Inches Total Internal Area Sq. In. 30 ..---~~.. 1 Cond. 53% 16 2-Cond.)

7 31% 09 3 or more 40% 12 % .53 .28 .16 i .21 1 1% I .86 .46 .80 i .27 .47 .34 .60 1% 2 2% 3 I I I i .63 , .82 3% 4 5 6 I i ! i , I TABLE 17 2 Maximum Number of Compact Conductors in Trade Sizes of Conduit or Tubing ! Insulation Type I .!TTX!TT XIT T X'T T T X I T T X,T T X 'T T H H ~IConductor l:.lH 'H H H Hi H H H'H H H H HIH H HH IHIH ~ H W H H! W H H W H H , W H H W H HSizeAWGor W H H W H N WN W N W' N W i N W N W N ~IW N H Wk'leml .. Conduit Trade Size i i 3112 in. 4 In. 11/4 in~ 1112 In. ! 2 in. 2112 In. 3 in. 9 13 11 12 15 156 5 7 6 15 18 184 4 4 4 7 8 8 9 11 11 11 13 132 5 6 6 7 8 83 3 3 i11 14 141 3 4 4 8 10 105 6 6 4 5 5 9 12 12110 3 3 3 7 8 8 210 12 15 153 4 4 5 7 7 8 10 103 3 5 6 63 3 3 7 8 8.

8 10 13 133/0 9 10 14 143 3 4 5 5 6 7 7410 9 11 11250 3 4 4 4 5 5 7 8 B 10 12 126 7 7300 3 3 3 3 4 4 8 9 10 9 11 11350 3 3 3 3 4 5 6 6 7 8 8 400 5 5 6 6 7 8 8 9 103 3 500 4 4 5 5 6 6 7 8 8 4 5 5 5 6 7I 600 3 4 4 4 4 4 6 6 6700 3 3 3 3 3 3 4 4 4 5 5 5750 3 3 3 4 4 4I 1000 17 2 TABLE 17-3 Conductor Cross-Sectional Areas (Based on Table 5, Chapter 9, 1987 NEC) APPROXIMATE AREA. SQUARE INCHES ' INSULATED CONDUCTOR WIRE ~-----------------1 SIZE,I Types Type AWG.: RHH & Type THHN Type kemil RHW' THW THWN XHHW' BARE -=~~~--~~~~ 12 ,038 ,025 ,012 ,017 ,005 10 ,046 ,031 ,018 ,022 ,008 8 ,085 ,060 ,037 ,046 ,017 6 124 082 052 062 027 , .. ,0424 .161 ,109.

9 084 .084 .182 .126 .099 ,099 .0533 2 .207 .147 ,118 .118 .067 1 .272 .203 .159 .159 .087 .311 ,237 .189 .189 ,109I/O 2/0 .358 .276 .226 ,226 .137i310 .415 .329 .271 .271 .173 4/0 ,484 .390 .328 .328 ,219 250 .592 .488 A03 ,403 , .260 300 ,684 .568 ,467 .467 .312 350 .762 .629 .531 ,531 .364 400 836 697 593 593 416 , .._ 50O ,983 ,832 .716 .716 ,520 600 ,879 .904 .626 700 1,336 .730 750 1,225 1,094 .782 900 , , .833 900 1,245 .933 1000 1,389 1250 1,767 1500 1750 2000 "'RHH and RHW without outer covering are the same as THW, the der'dting amounts given above, Note 10 to NEC Tables 310-16 to 310-31 specifies when the neutral must be counted as a current-carrying conductor), Rigid Aluminum Conduit Aluminum Rigid conduit has been widely used during the past five decades due to recognition that lightweight Aluminum conduit offers several advantages over steel" including reduced costs of installation, increased cor rosion resistance and improved ground path.

10 Advantages of Aluminum Conduit Aluminum 's combination of light weight, relatively high electrical and thermal conductivity, protective oxide Rigid Aluminum conduit film, and excellent ductility and machinability are basic factors in its present wide acceptance. The following material examines in some detail how these plus factors compare with steel. Composition and Manufacture: Rigid Aluminum con duit is usually extruded from the magnesium-silicide, 6063-Tl alloy, though other alloys can be used which meet UL requirements. Being an extrusion, Aluminum conduit is completely moisture-and vapor-tight. Also, extruded pipe provides a smooth, uniform interior surface, Weight Comparison: Aluminum conduit with Aluminum couplings weighs approximately one-third of its galvanized steel counterpart, and one-half that of steellMC, This dif ference in weight is reflected in substantially greater ease and cost savings in installation.