Conductors and Insulators Electronics Conductors and Insulators Copyright © Texas Education Agency, 2013. All rights reserved.  

Presentation Overview Terms and Definitions Conducting and Insulating Materials Functional Features of Electrical Conductors Functional Features of Electrical Insulators Applications of Conductors Types of Wire Conductors Wire Sizes and Gauge Numbers Properties of Conducting Materials Wire Resistance Desirable Properties of Wire Insulation Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. Terms and Definitions Resistivity or specific resistance The electrical resistance of a rod of conducting material having a specified length and cross-sectional area. Conductivity The capacity of a conducting rod of unit length and cross-sectional area to allow electrical current flow. Semiconductor A material having relatively high resistance at room temperature whose electrical characteristics can be changed and controlled by various techniques (such as by adding other elements called “impurities”). Examples include germanium and silicon, which function as transistors, chips, and diodes after the impurities arsenic or gallium are added to them. Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. Terms and Definitions Dielectric A material of very high resistance that is capable of holding or storing an electrical charge. Mil One thousandth (0.001) of an inch Circular mil (cmil) area The cross-sectional area of a wire calculated by squaring the wire diameter in mils. For example, the cmil area of a conductor having a diameter of 7.0 mils is 49.0 cmils (7.0 squared). (Note: This method of calculating cross-sectional area is used only for conducting wires, and is done as a convenience to avoid having to calculate cross-sectional area by means of the metric system and formula.) Copyright © Texas Education Agency, 2013. All rights reserved.  

Conducting and Insulating Materials Insulators (high resistance) Air or vacuum Bakelite Glass Mica Paper Rubber Shellac Semiconductors (medium resistance) Germanium Silicon Conductors (low resistance) Silver Copper Aluminum Gold Tungsten Nickel Iron Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. What is a Wire? A wire is the most common example of an electrical conductor. Wires are used in circuits to deliver voltage and current to where it is needed. Circuit components convert electrical energy into some other useful form of energy. Wires come in many different shapes and sizes. Copyright © Texas Education Agency, 2013. All rights reserved.  

Applications of Conductors Copyright © Texas Education Agency, 2013. All rights reserved.  

Types of Wire Conductors Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. Wire Resistance Specific resistance is a function of the area of a conductor measured in units of circular mils. The American Wire Gauge (AWG) gives the size of the conducting wire as a whole number. The larger the gauge number, the skinnier the wire. The smaller the gauge number, the thicker (fatter) the wire. There is a relationship between area in circular mils and the AWG, but it is complex. Wire resistance is a function of length. As length increases, wire resistance increases. A circular mil is more a way of comparing the size (area) of different conductors than a true measurement of area. Area for a wire (a circular conductor) is calculated by multiplying pi times the radius squared, where the radius is measured in thousandths of an inch. One mil equals one thousandth of an inch. A circular mil is used as a unit of area for a conductor. Copyright © Texas Education Agency, 2013. All rights reserved.  

Calculating Wire Resistance Principles The thicker the wire, the less its resistance. The longer the wire, the higher its resistance. Formula for wire resistance where R = total resistance ρ = specific resistance L = length of the wire A = cross-sectional area in circular mils   Specific resistance is a constant that depends on the physical characteristics of the wire used in the conductor. Common conductors have a table that will list the specific resistance. This is also called resistivity. Copyright © Texas Education Agency, 2013. All rights reserved.  

Functional Features of Electrical Conductors Many free electrons For good conduction of electricity Low resistance to electrical current Little voltage (IR) drop Low power dissipation Note that this example shows the difference between an ideal circuit (one with no wire resistance) and a real circuit (with wire resistance). About half a volt is lost, which means the light is slightly dimmer (99.6 Watts vs. 100 Watts). The loss is real, and consumers pay for it. The lower the wire resistance, the less loss, but larger wires also cost more during installation. Copyright © Texas Education Agency, 2013. All rights reserved.  

Wire Sizes and Gauge Numbers American Standard Wire Gauge is used to check wire sizes. Wire gauge chart Gauge numbers range from 1 to 40 Wire diameter is measured in mils (0.001 in.) Cross-sectional area is measured in Circular mils (cmils) The diameter in mils squared The higher the gauge number of a wire The smaller its wire diameter The smaller its cross-sectional area The higher its resistance A better (more readable) table for wire resistance characteristics—as a function of wire gauge—is given on the following pages. Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. WIRE TABLE FOR SOLID, ROUND COPPER CONDUCTORS Size Diameter Cross-sectional area Weight AWG inches cir. mils sq. inches lb/1000 ft ============================================= 4/0 -------- 0.4600 ------- 211,600 ------ 0.1662 ------ 640.5 3/0 -------- 0.4096 ------- 167,800 ------ 0.1318 ------ 507.9 2/0 -------- 0.3648 ------- 133,100 ------ 0.1045 ------ 402.8 1/0 -------- 0.3249 ------- 105,500 ----- 0.08289 ------ 319.5 1 -------- 0.2893 ------- 83,690 ------ 0.06573 ------ 253.5 2 -------- 0.2576 ------- 66,370 ------ 0.05213 ------ 200.9 3 -------- 0.2294 ------- 52,630 ------ 0.04134 ------ 159.3 4 -------- 0.2043 ------- 41,740 ------ 0.03278 ------ 126.4 5 -------- 0.1819 ------- 33,100 ------ 0.02600 ------ 100.2 6 -------- 0.1620 ------- 26,250 ------ 0.02062 ------ 79.46 7 -------- 0.1443 ------- 20,820 ------ 0.01635 ------ 63.02 8 -------- 0.1285 ------- 16,510 ------ 0.01297 ------ 49.97 9 -------- 0.1144 ------- 13,090 ------ 0.01028 ------ 39.63 10 ------- 0.1019 ------- 10,380 ------ 0.008155 ----- 31.43 11 -------- 0.09074 ------- 8,234 ------ 0.006467 ----- 24.92 12 -------- 0.08081 ------- 6,530 ------ 0.005129 ----- 19.77 13 -------- 0.07196 ------- 5,178 ------ 0.004067 ----- 15.68 14 -------- 0.06408 ------- 4,107 ------ 0.003225 ----- 12.43 15 -------- 0.05707 ------- 3,257 ------ 0.002558 ----- 9.858 16 -------- 0.05082 ------- 2,583 ------ 0.002028 ----- 7.818 1/0 is read as “one aut,” and is sometimes given as a single zero. 2/0 is read as “two aut” (sometimes given as two zeros, etc.). Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. WIRE TABLE FOR SOLID, ROUND COPPER CONDUCTORS Size Diameter Cross-sectional area Weight AWG inches cir. mils sq. inches lb/1000 ft ============================================== 17 -------- 0.04526 ------- 2,048 ------ 0.001609 ----- 6.200 18 -------- 0.04030 ------- 1,624 ------ 0.001276 ----- 4.917 19 -------- 0.03589 ------- 1,288 ------ 0.001012 ----- 3.899 20 -------- 0.03196 ------- 1,022 ----- 0.0008023 ----- 3.092 21 -------- 0.02846 ------- 810.1 ----- 0.0006363 ----- 2.452 22 -------- 0.02535 ------- 642.5 ----- 0.0005046 ----- 1.945 23 -------- 0.02257 ------- 509.5 ----- 0.0004001 ----- 1.542 24 -------- 0.02010 ------- 404.0 ----- 0.0003173 ----- 1.233 25 -------- 0.01790 ------- 320.4 ----- 0.0002517 ----- 0.9699 26 -------- 0.01594 ------- 254.1 ----- 0.0001996 ----- 0.7692 27 -------- 0.01420 ------- 201.5 ----- 0.0001583 ----- 0.6100 28 -------- 0.01264 ------- 159.8 ----- 0.0001255 ----- 0.4837 29 -------- 0.01126 ------- 126.7 ----- 0.00009954 ---- 0.3836 30 -------- 0.01003 ------- 100.5 ----- 0.00007894 ---- 0.3042 31 ------- 0.008928 ------- 79.70 ----- 0.00006260 ---- 0.2413 32 ------- 0.007950 ------- 63.21 ----- 0.00004964 ---- 0.1913 33 ------- 0.007080 ------- 50.13 ----- 0.00003937 ---- 0.1517 34 ------- 0.006305 ------- 39.75 ----- 0.00003122 ---- 0.1203 35 ------- 0.005615 ------- 31.52 ----- 0.00002476 — 0.09542 36 ------- 0.005000 ------- 25.00 ----- 0.00001963 — 0.07567 These tables primarily relate the wire gauge value to the cross-sectional area. Copyright © Texas Education Agency, 2013. All rights reserved.  

Properties of Conducting Materials The most important property is specific resistance because it is used in the calculation of wire resistance. The previous tables did not have this value. Note that the most common conductor is copper, so for most examples the following value is the only value used: 10.4 cmil-ohms per foot. The next most common conductor is made of aluminum, so this value might be used in an example also. Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved.   Ft cancel and cmils cancel, leaving only the unit of ohms.   Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. Example Problems What is the total resistance of 6,000 feet of 24 gauge copper wire at room temperature? What is the total resistance of 155 feet of 8 gauge aluminum wire at room temperature? What is the specific resistance of platinum if 200 feet of 12 gauge platinum wire is 1.93 Ω at room temperature? These are only examples. Make additional problems by inserting your own values into problems. Copyright © Texas Education Agency, 2013. All rights reserved.  

Functional Features of Electrical Insulators Few free electrons (poor conduction of electricity) High resistance to electrical current Hold and store an electrical charge High dielectric strength (high voltage breakdown point) Copyright © Texas Education Agency, 2013. All rights reserved.  

Desirable Properties of Wire Insulation High resistance Toughness Flexibility Non-brittleness with aging Insulation protects the wire and circuit from grounds and shorts. Insulation protects you from a potentially dangerous electric potential. Copyright © Texas Education Agency, 2013. All rights reserved.  

Copyright © Texas Education Agency, 2013. All rights reserved. Presentation Summary Terms and Definitions Conducting and Insulating Materials Functional Features of Electrical Conductors Functional Features of Electrical Insulators Applications of Conductors Types of Wire Conductors Wire Sizes and Gauge Numbers Properties of Conducting Materials Wire Resistance Desirable Properties of Wire Insulation Copyright © Texas Education Agency, 2013. All rights reserved.