Download Chapter 3 - Goodheart

Chapter 3
Introduction to Basic Electrical
Circuit Materials
Objectives
• Identify different conductor types.
• Determine the cross-sectional area of a
conductor.
• List the factors affecting resistance.
• Identify various insulation materials.
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Objectives
• List three special conductor pathways.
• Explain the manufacture of printed circuit
boards.
• Identify various switching devices.
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Objectives
• Identify various lighting devices.
• Identify different types of resistors.
• Determine the value of color-coded
resistors.
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Conductors
•
•
•
•
Copper
Silver
Aluminum (high-voltage lines)
Brass (electrical-mechanical equipment)
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Conductors (Cont.)
• Transfer electrons from one atom to another
within the conductor
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Computing Electrical Conductance
• G = 1/R
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• G: conductance in
siemens
• R: resistance in ohms
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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
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Conductor Sizes
• Gauged by cross-sectional area
• Determine amount of current the
conductor can handle before overheating
• Circular mil system
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Circular Mils (cmils)
• 1 mil = 0.001 inches
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Conductor Insulation
• Insulators
• Insulation on conductors as protective
coating
• Codings
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Insulation Codings
• Code letters
–
–
–
–
–
–
–
R
H
HH
A
T
M
UF
–C
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rubber
heat
high heat
asbestos
thermoplastic
oil resistant
underground
feeder
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
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Types of Conductors
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Conductor Resistance
•
•
•
•
Cross-sectional area of a conductor
Type of material
Length of conductor
Temperature of material
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Cross-Sectional Area of a Conductor
• Larger diameter has a greater current and lower
resistance
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Type of Material
• Affects conductance
and resistance
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Length of Conductor
• The longer the
conductor is, the
more resistance it has
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Temperature of Material
• Metals increase in resistance as ambient
temperature rises
• Metals exposed to low temperatures
become superconductors
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Safety Organizations and Standards
•
•
•
•
National Fire Protection Agency (NFPA)
National Electrical Code
Underwriters Laboratories Inc.
Occupational Safety and Health
Administration
• Conductor voltage drop standard
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National Fire Protection Agency
• NFPA dedicated to fire protection
• Provides information on how fires are
started
• Provides specific prevention methods
• Produces National Electrical Code
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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
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Underwriters Laboratories Inc.
• Independent
organization that
conducts tests for
public safety
• Tests equipment for
minimal safety design
standards
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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
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Conductor Voltage Drop
• NEC’s maximum voltage drop standard for
branch circuits
• A 3% voltage drop is the maximum permissible
KIL
CMA 
VD
•
•
•
•
•
CMA: area in cmils
K: material constant
I: amperage
L: length of wire
VD: voltage drop
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Review
What are conductors?
Pathways that allow current to flow
through an electrical circuit
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Review
What are four materials of which
conductors are typically made?
Copper, silver, aluminum, and brass
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Review
What is the unit used to measure
conductance?
The siemens
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Review
What unit is used to measure conductor
sizes?
Circular mils (cmils)
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Review
What materials do not conduct electrons
well?
Insulators
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Review
What is ambient temperature?
Temperature of material surrounding the
conductor, such as air, water, or soil
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Review
What organization produces the National
Electrical Code?
National Fire Protection Agency (NFPA)
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Review
What organization inspects equipment to
award its seal of approval?
Underwriters Laboratories Inc.
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Special Conductor Pathways
• Breadboards
• Printed circuit boards (PCBs)
• Chassis
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Breadboards
• Provide an easy
system for
constructing circuits
quickly
• Copper strips beneath
the holes are
conductor pathways
• Proto boards
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Printed Circuit Boards (PCBs)
• Strips of conductor
material attached to
an insulated board
• Components are
soldered to
conductive strips
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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
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Chassis
• Older way of
mounting components
• Part of the circuitry
• Not commonly used
as a conductor, but
still used in cars
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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
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Review
What is made from a thin layer of
conductor material, cut into strips, and
attached to an insulated board?
Printed circuit board (PCB)
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Common Circuit Devices
• Switches
• Connectors
• Circuit protection devices
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Switches
• Controlled by
actuators
• Single-pole singlethrow (SPST)
• Single-pole doublethrow (SPDT)
• Double-pole doublethrow (DPDT)
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Switch Ratings
• Ampacity rating
• Voltage rating
• Exceeding ratings causes switch to fail
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Connectors
• Vary by type or size of conductors
• Solderless connectors are common
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Connectors (Cont.)
• Mechanical connection to larger conductors
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Circuit Protection Devices
• Fuses
• Circuit breakers
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Fuses
• Time required to melt fuse link is inversely
proportional to amount of overload
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Circuit Breakers
• Resets
• Tripping methods
– Bimetallic strips
– Magnetism
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Review
How are switches controlled?
By actuators
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Review
What is the simplest type of switch?
Single-pole single-throw (SPST)
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Review
What are some common actuators?
Slide, toggle, rotary, and push button
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Review
What kind of switch has two common
connection points and can provide two
circuit paths simultaneously?
Double-pole double-throw (DPDT)
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Review
What are two types of switch ratings?
Ampacity and voltage
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Review
What are two common circuit protection
devices?
Fuses and circuit breakers
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Review
What is another name for a circuit breaker?
A reset
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Lighting
• Types of lighting systems
– Incandescent lamps
– Discharge lamps
• Measured in lumens
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Incandescent Lamps
• Developed by Thomas Edison
• Tungsten filament produces light
• Halogen lamps
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Halogen Lamps
• Tungsten filaments
produce light
• Halogen gas makes
filament last longer
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Discharge Lamps
• Light produced by energizing gases
• Types:
– Fluorescent lamps
– Compact fluorescent lamps
– Mercury vapor lamps
– Neon lamps
– Glow lamps
– Strobe lamps
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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
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Compact Fluorescent Lamps
(CFLs)
• Special fluorescent
lamps that can
replace incandescent
lamps
• Lower wattage than
incandescent lamps
• Less heat given off
than incandescent
lamps
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Mercury Vapor Lamps
• Two electrodes in an
arc tube
• Mercury and argon
gas
• Heat from electrodes
vaporizes mercury
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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
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Glow Lamps
•
•
•
•
Similar to neon lamps
Two electrodes in a short tube
Tube filled with neon or argon
Lower voltages than neon lamps
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Strobe Lamps
• Various sizes of glass
tubes
• Discharge of high dc
voltage through tube
• Exciters help produce
electrical arc
• Can generate 50,000
watts
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Lumens
• Lumens per watt (lpw)
• Light ratings
– Candelas
– Lumens
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Review
What type of lamp is a halogen lamp?
Incandescent lamp
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Review
What category of lamps are fluorescent,
neon, and mercury?
Discharge lamps
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Review
What component in a fluorescent lamp
limits current through the tube?
A ballast
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Review
What kind of lamp has two electrodes in
an arc tube that help vaporize the gas?
Mercury lamp
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Review
How are different colors achieved in a
neon lamp?
Different gases are used
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Review
How are electrical arcs produced in a
strobe lamp?
Exciters
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Resistors
• Many shapes and
sizes
• Various values of
material’s wattage
rating
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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
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Potentiometers
• Rotary knob varies
resistance
• Found in electronic
projects
• Similar to wire wound
resistors
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Thermistors
• Change resistance with temperature
• Prevent high current values
• Example: blow dryer
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Resistor Color Code
• Three to five color bands
• Bands represent different values
• Fourth band represents tolerance
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Review
What is the resistor’s ability to safely
dissipate heat?
Wattage rating
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Review
What are film resistors also called?
Surface-mounted resistors (SMRs)
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What kind of resistors have a sliding tap?
Adjustable resistors
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Review
What type of variable resistor is similar to
a wire wound resistor?
A potentiometer
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Review
What is a thermistor?
A special type of resistor that can change
resistance values as its temperature
changes
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What is a tolerance?
The precision to which a value can vary
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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.
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