Transcript Document

Chapter
28
Residential Electrical
Objectives
• Explain the characteristics of electricity in terms
of amperes, volts, resistance, and watts.
• Describe how electricity is delivered to and
distributed through residential structures.
• Identify the three types of branch circuits used in
a residential structure.
• Calculate circuit requirements for a residence.
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Objectives
• Describe the types of outlets and switches. used
in a residence and their typical locations.
• Explain the advantages of low-voltage exterior
lighting.
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Permission granted to reproduce for educational use only.
Introduction
• Planning for electrical needs of home requires
basic understanding of:
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Related terms
Electrical requirements
Code restrictions
Safety considerations
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Electrical Terms
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Ampere (amp)
Ohms
Voltage
Volt
Watts
– Amp  Volts = Watts
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Service Entrance and
Distribution Panel
• Service entrance
– Fittings and conductors that bring electricity into
building
• Distribution panel
– Receives electricity and distributes it to various
points in house through individual circuits
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Permission granted to reproduce for educational use only.
Service Entrance and
Distribution Panel
• Circuits consist of conductors that permit
flow of electricity
• Distribution panel also contains main
disconnect switch fuse or breaker
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Service Entrance Equipment
• Residence may have 120- or 240-volt service
– Two conductors required for 120-volt service
– Three conductors required for 240-volt service
• 240-volt service is recommended
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Service Entrance Equipment
• Incoming electrical service usually enters house
through meter
• Service may be overhead or underground
• Conductors are generally run from service drop or
from underground cable through run of heavy
conduit
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Underground Service Layout
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Overhead Service Layout
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Service Entrance Designs
• Service head is used if service entrance is located
along eaves line of single-story home
• Service drop must be:
– At least 10 above grade at service entrance
– 12 above residential property and driveways
• Conductors must be at least 3 away from
structures where they may be touched
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Conductor Sizing
• Conductors bring current from service head or
underground cable to meter and then to
distribution panel
• Conductor diameter increases as designation
number decreases
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Conductor Sizing
• Smallest circuit conductor permitted by NEC is 14
AWG
• 12 AWG is recommended for branch lighting
circuits
• If wire is too small for current, fire may result
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Permission granted to reproduce for educational use only.
Distribution Panel
• Conductors from meter run to distribution panel
• Electricity is distributed to various points in house
through branch circuits
• Distribution conductors are color-coded
• NEC recommends minimum of 100-amp service
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Permission granted to reproduce for educational use only.
Typical Distribution Panel
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Overcurrent Protection
• Fuse
– Fusible link
– Cannot be reused
• Circuit breaker
– Found in most new
homes
– Can be reset
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Branch Circuits
• Branch circuits
– Lighting circuit
– Small-appliance circuit
– Individual circuit
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Lighting Circuits
• Serve permanently installed lighting fixtures and
outlets for amps, radios, TVs, etc.
• Frequently 12 AWG copper wire conductor with
20-amp overcurrent protection
• Three watts of lighting power per sq. ft. of floor
space is required
• One lighting circuit for each 400 sq. ft. is good rule
of thumb
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Permission granted to reproduce for educational use only.
Small-Appliance Circuits
• Located in the kitchen, garage, or shop
• Usually above a countertop or workbench
• Designed for tools and appliances that require
large amounts of current
– Electric fry pans, blenders, electric drills, power
hand saws
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Permission granted to reproduce for educational use only.
Small-Appliance Circuits
• 12 AWG copper wire with 20-amp overcurrent
protection
• Lighting outlets should not be operated from these
circuits
• NEC requires at least two small-appliance circuits
in kitchen
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Permission granted to reproduce for educational use only.
Individual Circuits
• Serve single, permanently • Examples:
– Air conditioner
installed appliances or
– Clothes washer
equipment
– Dishwasher
• Each appliance has its
– Furnace
own circuit
– Range
– Table saw
– Water heater
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Permission granted to reproduce for educational use only.
Individual Circuits
• Any 120-volt, permanently connected appliance
that is rated over 1400 watts or starts
automatically must also have its own circuit
• Individual circuits may be 120 or 240 volts
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Circuit Requirement Calculations
• Several factors affect size of service entrance and
number of branch circuits
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Size of house
Size and number of appliances
Lighting to be installed
Planned future expansions
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Circuit Requirement Calculations Example
• Size of residence = 1500 square feet
• Lighting circuits: (3 × 1500 = 4500 watts)
• Small-appliance circuits: 2 for kitchen (120 volts x
20 amp × 2 = 4800 watts)
• Individual circuits: 7 circuits (totaling 22,000 watts)
• Total = 31,300 watts/240 volts = 130.4 amps
• House will require 150 amp service
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Employability
• Professional language
– No slang or profanity
– Workplace communications should be polite,
grammatically correct, and respectful
– Professional language is essential to employability
and workplace success
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Outlets and Switches
• Outlets, switches, and joints where conductors are
spliced must be housed in electrical box
• Lighting fixtures must be mounted on box
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Outlets
• Lighting outlet
• Receptacle outlet
– Also called receptacle or convenience outlet
– General-purpose
• Special-purpose outlet
– Examples: Telephone jacks, TV outlets, burglar
alarm systems
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GFCI
• Ground-fault circuit interrupter (GFCI)
– Safety device that continually monitors flow of
current in circuit
• GFCI responds in 1/30th of a second
• GFCIs can be placed as any receptacle
• NEC defines when and where GFCIs are used
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GFCI Locations
• Outdoors
• Kitchen
– All receptacles serving
countertop surfaces
• Bathroom
– All receptacles
• Garage
– All receptacles
– All receptacles that
are readily accessible
• Unfinished basements
and crawl spaces
– All receptacles except
for receptacle
supplying permanently
installed alarm system
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Switches
• Single-pole switch
• Three-way switch
– Allows fixture to be switched from two locations
• Dimmer switch
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Locating Outlets and Switches
• Placement is affected by codes, furniture
arrangements, and personal preference
• NEC requires that no point along a wall should be
more than 6′ away from a receptacle outlet
– 8′ is recommended
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Locating Outlets and Switches
• Receptacle outlets:
– 12" or 18" above floor, except for kitchen
• Switches
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48" above floor, in a logical place
30" to 40" is preferred for wheelchair users
Do not mount in inaccessible locations
Do not locate bathroom switches within reach of
bathtub or shower
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Permission granted to reproduce for educational use only.
Low-Voltage Exterior Lighting
• Good outdoor lighting is both functional and
aesthetic
• Low voltage lighting system consists of lights,
wire, one or more controllers, and transformers
• More expensive than 120-volt lighting, but safer
and easier to install
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Permission granted to reproduce for educational use only.
Planning Low-Voltage
Exterior Lighting
• Decide where light is needed for safety, security,
and activities
• Then plan for decorative lighting
• Try to avoid glare
• Outdoor light fixtures are either decorative or
hidden
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Permission granted to reproduce for educational use only.
Planning Low-Voltage
Exterior Lighting
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Use shielded fixtures to hide light source
Hide fixtures where they cannot be seen
Use more, smaller lights
Remember safety when planning lighting
Use light to shape an outdoor space
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Permission granted to reproduce for educational use only.
Low-Voltage Wiring Considerations
• Lights farther away from transformer produce less
light due to voltage drop
• Put no more than 100 watts of lighting on one leg
of tee
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Low-Voltage Wiring Considerations
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Choose proper size transformer
Use GFCI receptacle as power source
Consider indoor switch and timer combination
Try to prevent corrosion before it starts
Call utility company before digging
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Low-Voltage Wiring Considerations
• Leave a little extra wire in layout
• After checking entire setup, bury wires at least 6"
deep
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Green Architecture
• Passive energy sources
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Solar, wind, or geothermal
Research what systems are available
Check code restrictions
May cost more but can be much more sustainable
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