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1. Basic Principles of Electricity1.7 ELECTRICAL SYSTEMS1.7.1 Medium VoltageThe most widely used medium voltage (2.4 to 35 kV) alternating current (AC) electrical distribution systems in North Americaare illustrated below:Figure 1.1 – Three phase wye(star), three wireFigure 1.2 – Three phase delta,three wireFigure 1.3 – Three phase star,four wire, grounded neutral– Three(0-2,000phase wyeFigure1.2 – Three phase delta,Typical low Figurevoltage1.1systemsV) are illustratedbelow:(star), three wirethree wire1.7.2 Low VoltageTypical(0 to2,000 V)V)areareillustratedbelow:Typicallow-voltagelow re 1.3 – Three phase star,four wire, grounded neutralFigure 1.4 – Three phase wye (star),three wire, grounded neutralFigure 1.5 – Three phase delta,four wire, grounded neutralFigure 1.4 – Three phase wye (star),three wire, grounded neutralFigure 1.5 – Three phase delta,four wire, grounded neutral3

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2. Conductors2. CONDUCTORS2.1Strand Types72.1.1 Concentric Strand2.1.2 Bunch Strand2.1.3 Rope Strand2.1.4 Sector Conductor2.1.5 Segmental Conductor2.1.6 Annular Conductor2.1.7 Compact Strand2.1.8 Compressed Strand777778882.2Coatings102.3Tensile Strength of Copper Wire102.4Copper Strand Properties112.4.1 Strand Classes2.4.2 Solid Copper2.4.3 Class B, C and D Copper Strand2.4.4 Class H Copper2.4.5 Class I Copper2.4.6 Class K Copper2.4.7 Class M Copper11121417192021Aluminum Strand Properties222.5.1 Solid Aluminum2.5.2 Class B Aluminum2.5.3 ACSR222324Additional Conductor Properties262.6.1 Stranding, Diameter, Area and DC Resistance (32 through 4/0 AWG)2.6.2 Stranding, Diameter, Area, DC Resistanceand Weight (20 AWG through 2,000 kcmil)2.6.3 IEC Stranding262.52.628315

2. ConductorsCONDUCTORSThe conductor is the metallic component of cables through which electrical power or electrical signals are transmitted. Conductor size isusually specified by American Wire Gauge (AWG), circular mil area or in square millimeters.AWGThe American Wire Gauge (sometimes called Brown and Sharpe or B. and S.) is used almost exclusively in the USA for copper and aluminumwire. The Birmingham Wire Gauge (BWG) is used for steel armor wire.The diameters according to the AWG are defined as follows: The diameter of size 4/0 (sometimes written 0000) equals 0.4600 inch and thatof size #36 equals 0.0050 inch; the intermediate sizes are found by geometric progression. That is, the ratio of the diameter of one size tothat of the next smaller size (larger gauge number) is:390.4600 1.1229320.0050Circular MilSizes larger than 4/0 are specified in terms of the total area of a cross-section of the copper in circular mils (cmil). A circular mil is a unit of4 equal to the area of a circle one mil in diameter. It is p/4 (equal to 0.7854) of a square mil (one mil 0.001 inch). The area of a circleareain circular mils is therefore equal to the square of its diameter in mils. A solid wire one inch in diameter has an area of 1,000,000 cmils,whereas one square inch equals 4/p x 1,000,000 cmils (equal to 1,273,200 cmils). MillimetersSquare2Metric sizes are given in terms of square millimeters (mm ).Conductor CharacteristicsRelative electrical and thermal conductivities of common metal conductors are as follows:Table 2.1–Relative Electrical and Thermal Conductivities of Common Conductor MaterialsMetalSilverCopper (annealed)Copper (hard IronPlatinumTinSteelLeadRelative Electrical Conductivity at 20 C1061009772623929252318171615128Relative Thermal Conductivity at 20 C108100–7656412915241717181713-179Additional electrical properties can be found in Section 7 of this handbook.6

2. Conductors2.1 STRAND TYPES2.1.1 Concentric StrandA concentric stranded conductor consists of a central wire or core surrounded by one or morelayers of helically laid wires. Each layer after the first has six more wires than the precedinglayer. Except in compact stranding, each layer is usually applied in a direction opposite tothat of the layer under it.If the core is a single wire and if it and all of the outer strands have the same diameter, thefirst layer will contain six wires; the second, twelve; the third, eighteen; etc.Figure 2.1–Concentric Strand2.1.2 Bunch StrandThe term bunch stranding is applied to a collection of strands twisted together in the samedirection without regard to the geometric arrangement.Figure 2.2–Bunch Strand2.1.3 Rope StrandA rope stranded conductor is a concentric stranded conductor each of whose componentstrands is itself stranded. A rope stranded conductor is described by giving the number ofgroups laid together to form the rope and the number of wires in each group.Figure 2.3–Rope Strand2.1.4 Sector ConductorA sector conductor is a stranded conductor whose cross-section is approximately the shape ofa sector of a circle. A multiple conductor insulated cable with sector conductors has asmaller diameter than the corresponding cable with round conductors.Figure 2.4–Sector Conductor2.1.5 Segmental ConductorA segmental conductor is a round, stranded conductor composed of three or four sectorsslightly insulated from one another. This construction has the advantage of lower ACresistance due to increased surface area and skin effect.Figure 2.5–Segmental Conductor7

2. Conductors2.1.6 Annular ConductorAn annular conductor is a round, stranded conductor whose strands are laid around asuitable core. The core is usually made wholly or mostly of nonconducting material. Thisconstruction has the advantage of lower total AC resistance for a given cross-sectional area ofconducting material due to the skin effect.Figure 2.6–Annular Conductor2.1.7 Compact StrandA compact stranded conductor is a round or sector conductor having all layers stranded inthe same direction and rolled to a predetermined ideal shape. The finished conductor issmooth on the surface and contains practically no interstices or air spaces. This results in asmaller diameter.Figure 2.7–Compact Conductor2.1.8 Compressed StrandCompressed conductors are intermediate in size between standard concentric conductors and compact conductors. A comparison is shownbelow:SolidCompactCompressedConcentricFigure 2.8–Comparative Sizes and Shapes of 1,000 kcmil ConductorsIn a concentric stranded conductor, each individual wire is round and considerable space exists between wires. In a compressed conductor,the conductor has been put through a die that “squeezes out” some of the space between wires. In a compact conductor each wire ispreformed into a trapezoidal shape before the wires are stranded together into a finished conductor. This results in even less space betweenwires. A compact conductor is, therefore, the smallest in diameter (except for a solid conductor, of course). Diameters for common conductorsizes are given in Table 2.2.8

2. ConductorsTable 2.2–Diameters for Copper and Aluminum ConductorsConductor Size(AWG)Nominal Diameters (in.)(kcmil)SolidClass BCompactClass BCompressedClass 00001.0601.1171.152Sources: A STM B8 and B496ICEA S-95-658 (NEMA WC-70)9

2. Conductors2.2 COATINGSThere are three materials commonly used for coating a copper conductor: tin, silver and nickel.Tin is the most common and is used for improved corrosion resistance, solderability and to reduce friction between strands in flexible cables.Silver-plated conductors are used in high-temperature environments (150 C–200 C). It is also used for high-frequency applications wheresilver’s high conductivity (better than copper) and the “skin effect” work together to reduce attenuation at high frequencies.Nickel coatings are used for conductors that operate between 200 C and 450 C. At these high temperatures, copper oxidizes rapidly if notnickel plated. One drawback of nickel is its poor solderability and higher electrical resistance.2.3 TENSILE STRENGTH OF COPPER WIRETable 2.3–Tensile Strength of Copper Wire10SizeSoft or AnnealedMedium Hard DrawnHard Drawn(AWG)Max. Breaking Load (lb.)Min. Breaking Load (lb.)Min. Breaking Load 4.485.47322.012.903.53341.251.822.20360.791.161.40

2. Conductors2.4 COPPER STRAND PROPERTIES2.4.1 Strand ClassesTable 2.4–Strand ructionClassConcentric layRope lay with concentric stranded membersConstructionClassRope lay withbunch strandedmembersIUp to 2,000KBunch strandedApplicationAAFor bare conductors – usually used in overhead lines.AFor bare conductors where greater flexibility than is afforded by Class AAis required.BF or conductors insulated with various materials such as EP, XLP, PVC, etc.This is the most common class.CFor conductors where greater flexibility is required than is provided by Class B.DN/AGConductor constructions having a range of areas from 5,000,000 circularmils and employing 61 stranded members of 19 wires each down to No.14 AWG containing seven stranded members stranded members of sevenwires each. Typical uses are for portable (flexible) conductors and similarapplications.HConductor constructions having a range of areas from 5,000,000 circularmils and employing 91 stranded members of 19 wires each down to No. 9AWG containing 19 stranded members of seven wires each. Typical uses arefor rubber-jacketed cords and conductors where flexibility is required, suchas for use on take-up reels, over sheaves and apparatus conductors.Conductor SizeIndividual Wire SizeApplication(kcmil/AWG)Diameter (in.)(AWG)0.020124Typical use is for special apparatus cable.Up to 2,0000.010030Typical use is for portable cord.MUp to 1,0000.006334Typical use is for welding cable.I7, 8, 9, 100.020124Rubber-covered conductors.J10, 12, 14, 16, 18, 200.012628Fixture wire.K10, 12, 14, 16, 18, 200.010030Fixture wire, flexible cord and portablecord.L10, 12, 14, 16, 18, 200.008032Fixture wire and portable cord with greaterflexibility than Class K.M14, 16, 18, 200.006334Heater cord and light portable cord.O16, 18, 200.005036Heater cord with greater flexibility thanClass M.P16, 18, 200.004038More flexible conductors than provided inpreceding classes.Q18, 200.003140Oscillating fan cord. Very good flexibility.Source: Compiled from ASTM standards listed11

2. Conductors2.4.2 Solid CopperTable 2.5–Standard Nominal Diameters and Cross-Sectional Areas of Solid Copper WireSize(AWG)Diameter(mils)Cross-Sectional Area(kcmils)Weight(lb./1,000 ft.)Breaking StrengthSoft or Annealed 98Continued on next page 12

2. ConductorsTable 2.5–Standard Nominal Diameters and Cross-Sectional Areas of Solid Copper Wire Sectional Area(kcmils)Weight(lb./1,000 ft.)Breaking StrengthSoft or Annealed ��–461.570.00246––Source: ASTM B258, Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Usedas Electrical Conductors13

2. Conductors2.4.3 Class B, C and D Copper StrandTable 2.6–Class B Concentric-Lay-Stranded Copper ConductorsSizeNumber of Wires(AWG or kcmi)Diameter of Each StrandWeight(mils)(lb./1,000 ft.)Nominal Overall ntinued Table 2.6–Class B Concentric-Lay-Stranded Copper Conductors (Continued)14

2. ConductorsSizeNumber of Wires(AWG or kcmi)3/019Diameter of Each StrandWeight(mils)(lb./1,000 ft.)Nominal Overall 0712.13.1540.0363Source: ASTM B8 Specification for Concentric-Lay-Stranded Copper Conductors, Hard, Medium-Hard, or Soft15

2. ConductorsTable 2.7–Copper Strand DiametersConductor SizeStranding(AWG)(kcmil)Class B .3620.3720.3740.3741/0105.6Class BCompressed (in.)Class B Concentric Class C Concentric Class D 1.1531.153–1,100–1.1731.2091.2101.211Continued 16

2. ConductorsTable 2.7–Copper Strand Diameters (Continued)Conductor Size(AWG)Stranding(kcmil)Class B Compact(in.)Class BCompressed (in.)Class B Concentric Class C Concentric Class D 3,000–1.9381.9981.9981.9982.4.4 Class H CopperTable 2.8–Class H Rope-Lay-Stranded Copper ConductorsSize (AWG or kcmil)Number of StrandsConstructionNominal Diameter ofEach Strand (in.)Nominal O.D. (in.)Nominal Weight(lb./1,000 ed 17

2. ConductorsTable 2.8–Class H Rope-Lay-Stranded Copper Conductors (Continued)Size (AWG or kcmil)Number of StrandsConstructionNominal Diameter ofEach Strand (in.)Nominal O.D. (in.)Nominal Weight(lb./1,000 1002,0001,15961x190.04151.8686,400Source: ICEA S-95-658 (NEMA 70) Appendix K18

2. Conductors2.4.5 Class I CopperTable 2.9–Class I (24 AWG Strands) Rope-Lay-Stranded Copper ConductorsSize (AWG or 19x7x3319x7x3419x7x3619x7x37Nominal Number of 4,5224,7884,921Nominal 0.D. (in.)0.1250.1380.1560.1850.2070.2350.2630.291

If you are interested in downloading the PDF version of this book, please visit WireXpress.com. . is the flow of electric current along a conductor. This electric current takes the form of free electrons that transfer from one atom to the next. Thus, the more free electrons a material has, the better it co