1. Conductors and Insulators
Electronics
Conductors and Insulators
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2. 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
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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.
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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.)
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5. 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
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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.
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7. Applications of Conductors
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8. Types of Wire Conductors
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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.
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10. 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.
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11. 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.
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12. 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.
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WIRE TABLE FOR SOLID, ROUND COPPER CONDUCTORS
Size Diameter Cross-sectional area Weight
AWG inches cir. mils sq. inches lb/1000 ft
=============================================
4/ ,
3/ ,
2/ ,
1/ , , , , , , , , , , , , , , , , ,
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.).
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WIRE TABLE FOR SOLID, ROUND COPPER CONDUCTORS
Size Diameter Cross-sectional area Weight
AWG inches cir. mils sq. inches lb/1000 ft
============================================== , , , , — —
These tables primarily relate the wire gauge value to the cross-sectional area.
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15. 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.
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Ft cancel and cmils cancel, leaving only the unit of ohms.
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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.
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18. 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)
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19. 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.
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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
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