chapter 3 introduction to basic electrical circuit materials

Chapter 3

Introduction to Basic Electrical Circuit Materials

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Objectives

• Identify different conductor types.

• Determine the cross-sectional area of a conductor.

• List the factors affecting resistance.

• Identify various insulation materials.


Objectives

• List three special conductor pathways.

• Explain the manufacture of printed circuit boards.

• Identify various switching devices.


Objectives

• Identify various lighting devices.

• Identify different types of resistors.

• Determine the value of color-coded resistors.


Conductors

• Copper

• Silver

• Aluminum (high-voltage lines)

• Brass (electrical-mechanical equipment)


Conductors (Cont.)

• Transfer electrons from one atom to another within the conductor


Computing Electrical Conductance

• G = 1/R • G: conductance in siemens

• R: resistance in ohms


Lesson in Safety

• Your body can conduct electricity– Electric current can flow into one hand,

through your body, and out your other hand– Can be fatal

• Keep one hand in a pocket to avoid shock

• Stand on insulated materials when working with high voltage


Conductor Sizes

• Gauged by cross-sectional area

• Determine amount of current the conductor can handle before overheating

• Circular mil system


Circular Mils (cmils)

• 1 mil = 0.001 inches


Conductor Insulation

• Insulators

• Insulation on conductors as protective coating

• Codings


Insulation Codings

• Code letters– R rubber– H heat– HH high heat– A asbestos– T thermoplastic– M oil resistant– UF underground

feeder– C corrosion

resistant

• Color coding– Used to trace the

insulation through a building

– Can represent certain voltages, polarities, or grounding conductors

– Governed by building codes or manufacturing associations


Types of Conductors


Conductor Resistance

• Cross-sectional area of a conductor

• Type of material

• Length of conductor

• Temperature of material


Cross-Sectional Area of a Conductor

• Larger diameter has a greater current and lower resistance


Type of Material

• Affects conductance and resistance


Length of Conductor

• The longer the conductor is, the more resistance it has


Temperature of Material

• Metals increase in resistance as ambient temperature rises

• Metals exposed to low temperatures become superconductors


Safety Organizations and Standards

• National Fire Protection Agency (NFPA)

• National Electrical Code

• Underwriters Laboratories Inc.

• Occupational Safety and Health Administration

• Conductor voltage drop standard


National Fire Protection Agency

• NFPA dedicated to fire protection

• Provides information on how fires are started

• Provides specific prevention methods

• Produces National Electrical Code


National Electrical Code

• Regulations to ensure safety

• Standards apply to design of electrical systems

• Adopted by government agencies at city, county, state, and federal levels


Underwriters Laboratories Inc.

• Independent organization that conducts tests for public safety

• Tests equipment for minimal safety design standards


Occupational Safety and Health Administration

• Part of U.S. Department of Labor

• Responsible for worker safety

• Conducts on-site inspections

• Authority to inspect and fine industries that do not meet safety standards


Conductor Voltage Drop

• NEC’s maximum voltage drop standard for branch circuits

• A 3% voltage drop is the maximum permissible

• CMA: area in cmils• K: material constant• I: amperage• L: length of wire• VD: voltage drop

VD

LIKCMA


Review

What are conductors?

Pathways that allow current to flow through an electrical circuit


Review

What are four materials of which conductors are typically made?

Copper, silver, aluminum, and brass


Review

What is the unit used to measure conductance?

The siemens


Review

What unit is used to measure conductor sizes?

Circular mils (cmils)


Review

What materials do not conduct electrons well?

Insulators


Review

What is ambient temperature?

Temperature of material surrounding the conductor, such as air, water, or soil


Review

What organization produces the National Electrical Code?

National Fire Protection Agency (NFPA)


Review

What organization inspects equipment to award its seal of approval?

Underwriters Laboratories Inc.


Special Conductor Pathways

• Breadboards

• Printed circuit boards (PCBs)

• Chassis


Breadboards

• Provide an easy system for constructing circuits quickly

• Copper strips beneath the holes are conductor pathways

• Proto boards


Printed Circuit Boards (PCBs)

• Strips of conductor material attached to an insulated board

• Components are soldered to conductive strips


Construction of PCBs

• Copper foil used as conductor material

• Resist material put on copper foil for circuit design

• Etchant removes all of copper but circuit design

• Photographic process uses light exposure and solvent to make circuit design


Chassis

• Older way of mounting components

• Part of the circuitry• Not commonly used

as a conductor, but still used in cars


Review

What is a breadboard?

A pathway that consists of a series of holes aligned in rows across the entire surface of an insulation material


Review

What is made from a thin layer of conductor material, cut into strips, and attached to an insulated board?

Printed circuit board (PCB)


Common Circuit Devices

• Switches

• Connectors

• Circuit protection devices


Switches

• Controlled by actuators

• Single-pole single-throw (SPST)

• Single-pole double-throw (SPDT)

• Double-pole double-throw (DPDT)


Switch Ratings

• Ampacity rating

• Voltage rating

• Exceeding ratings causes switch to fail


Connectors

• Vary by type or size of conductors• Solderless connectors are common


Connectors (Cont.)

• Mechanical connection to larger conductors


Circuit Protection Devices

• Fuses

• Circuit breakers


Fuses

• Time required to melt fuse link is inversely proportional to amount of overload


Circuit Breakers

• Resets• Tripping methods

– Bimetallic strips– Magnetism


Review

How are switches controlled?

By actuators


Review

What is the simplest type of switch?

Single-pole single-throw (SPST)


Review

What are some common actuators?

Slide, toggle, rotary, and push button


Review

What kind of switch has two common connection points and can provide two circuit paths simultaneously?

Double-pole double-throw (DPDT)


Review

What are two types of switch ratings?

Ampacity and voltage


Review

What are two common circuit protection devices?

Fuses and circuit breakers


Review

What is another name for a circuit breaker?

A reset


Lighting

• Types of lighting systems– Incandescent lamps– Discharge lamps

• Measured in lumens


Incandescent Lamps

• Developed by Thomas Edison• Tungsten filament produces light• Halogen lamps


Halogen Lamps

• Tungsten filaments produce light

• Halogen gas makes filament last longer


Discharge Lamps

• Light produced by energizing gases

• Types:– Fluorescent lamps– Compact fluorescent lamps– Mercury vapor lamps– Neon lamps– Glow lamps– Strobe lamps


Fluorescent Lamps

• Filament or electrode• Air removed from tube• Tube filled with inert

gas and mercury• Mercury vaporized by

heat• Ballast in tube limits

current


Compact Fluorescent Lamps (CFLs)

• Special fluorescent lamps that can replace incandescent lamps

• Lower wattage than incandescent lamps

• Less heat given off than incandescent lamps


Mercury Vapor Lamps

• Two electrodes in an arc tube

• Mercury and argon gas

• Heat from electrodes vaporizes mercury


Neon Lamps

• Two electrodes in a long glass tube

• Shaped for various applications

• Tube filled with neon gas

• High voltage to create current

• Other gases can be used for different colors


Glow Lamps

• Similar to neon lamps

• Two electrodes in a short tube

• Tube filled with neon or argon

• Lower voltages than neon lamps


Strobe Lamps

• Various sizes of glass tubes

• Discharge of high dc voltage through tube

• Exciters help produce electrical arc

• Can generate 50,000 watts


Lumens

• Lumens per watt (lpw)

• Light ratings– Candelas– Lumens


Review

What type of lamp is a halogen lamp?

Incandescent lamp


Review

What category of lamps are fluorescent, neon, and mercury?

Discharge lamps


Review

What component in a fluorescent lamp limits current through the tube?

A ballast


Review

What kind of lamp has two electrodes in an arc tube that help vaporize the gas?

Mercury lamp


Review

How are different colors achieved in a neon lamp?

Different gases are used


Review

How are electrical arcs produced in a strobe lamp?

Exciters


Resistors

• Many shapes and sizes

• Various values of material’s wattage rating


Types of Resistors

• Molded composition resistors• Film resistors, or surface-mounted resistors (SMRs)• Wire wound resistors• Adjustable resistors

– A sliding tap allows the resistance to be varied


Potentiometers

• Rotary knob varies resistance

• Found in electronic projects

• Similar to wire wound resistors


Thermistors

• Change resistance with temperature

• Prevent high current values

• Example: blow dryer


Resistor Color Code

• Three to five color bands• Bands represent different values• Fourth band represents tolerance


Review

What is the resistor’s ability to safely dissipate heat?

Wattage rating


Review

What are film resistors also called?

Surface-mounted resistors (SMRs)


Review

What kind of resistors have a sliding tap?

Adjustable resistors


Review

What type of variable resistor is similar to a wire wound resistor?

A potentiometer


Review

What is a thermistor?

A special type of resistor that can change resistance values as its temperature changes


Review

What is a tolerance?

The precision to which a value can vary


For Discussion

• What items other than an automobile could use a chassis as a conductor?

• Discuss why a good understanding of the relationship among conductors, insulators, and semiconductors is important.

chapter 3 introduction to basic electrical circuit materials

Documents

educational use

conductor slide

standard slide

inchesmil slide

lower resistance slide

national electrical

high voltage slide

conductor sizes