Transcript Arch21

Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.
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Chapter 21
Residential
Electrical
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Permission granted to reproduce for educational use only
Chapter 21 Overview
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Introduction
Electrical Terms
Service Entrance and Distribution Panel
Branch Circuits
Circuit Requirement Calculations
Outlets and Switches
Ground-Fault Circuit Interrupter (GFCI)
Low Voltage Exterior Lighting
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Learning Objectives
• Define typical residential electrical
terms.
• Plan for the electrical needs of a
modern home.
• Identify and explain the three types of
electrical circuits used in a residential
structure.
(continued)
4
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Learning Objectives
• Calculate circuit requirements for a
residence.
• Explain the advantages and
disadvantages of low voltage exterior
lighting.
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Introduction
• Planning for the electrical needs of a
home requires a basic understanding of
several factors.
– Understanding related terms.
– Electrical requirements.
– Code restrictions.
– Safety considerations.
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Electrical Terms
• You must know the following terms to
design an electrical plan:
– Ampere (amp).
– Circuit .
– Circuit breaker.
– Conductor.
– Convenience outlet.
– Fuse.
– Lighting outlet.
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(continued)
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Electrical Terms
– Ohm.
– Receptacle.
– Service drop.
– Service entrance.
– Service panel.
– Voltage.
– Watt.
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Service Entrance and Panel
• The most basic part of a residential
electrical system is the service entrance
and distribution panel.
• The service entrance may be one of two
types: circuit breaker or fuse.
• Circuit breakers provide overcurrent
protection if the load is too high.
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Panel and Breakers
(Square D Company)
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Service Entrance and Panel
• A residence may have 120 or 240 volt
service.
• Two conductors are required for 120
volt service.
• Three conductors are required for 240
volt service.
• 240 volt service is recommended.
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Residential Electrical Service
• Two voltages are available from a 240
volt, 3-wire service drop.
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Service Entrance and Panel
• Electrical service conductors first
terminate at the meter.
• Service may be overhead or
underground.
• In an overhead service drop, the cables
must be at least 10' above the ground at
all points and 12' above driveways.
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Service Entrance Types
• Underground service.
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Service Entrance Types
• Overhead service.
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Electrical Conductors
• Electrical conductor
(cable) is used to bring
the current from the
service head or
underground cable to the
meter and then to the
distribution panel.
• Copper or aluminum
electrical cable may be
used.
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Conductor Sizes
• Conductor diameter increases as the
designation number decreases. The
smallest circuit conductor permitted by
the NEC is Number 14.
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Distribution Panel
• Conductors from the meter terminate at
the distribution panel.
• Electricity is distributed from the
distribution panel to various points in the
house through branch circuits.
• The main disconnect switch is located in
the distribution panel.
• The NEC recommends a minimum of
100 amp service.
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Typical Distribution Panel
(Square D Company)
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Circuit Breakers
• Circuit breakers are available in a
variety of sizes and types.
(Square D Company)
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Circuit Breakers and
Distribution Panel
• Common
distribution panels
designed for
circuit breakers
include the main
breaker, 240 volt
circuits, and 120
volt circuits.
(Square D Company)
© Goodheart-Willcox Co., Inc.
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Branch Circuits
• A branch circuit is one of several
individual circuits from the distribution
panel.
• The NEC specifies three types of
branch circuits for residential structures.
– Lighting circuits.
– Special appliance circuits.
– Individual appliance circuits.
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Lighting Circuits
• Used primarily for lighting.
• Serve permanently installed lighting
fixtures.
• Serve receptacle outlets for lamps,
radios, and clocks, but not kitchen
appliances.
(continued)
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Lighting Circuits
• Generally use Number 12 copper wire
with 20 amp overcurrent protection. This
provides 2400 watts of lighting capacity
(120 x 20 = 2400).
• Three watts of lighting power per square
foot of floor space is required, but five or
six watts is recommended.
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Special Appliance Circuits
• Located in the kitchen, garage, or shop.
• Usually above a countertop or
workbench.
• Designed for electric fry pans, mixers,
and blenders, as well as electric drills
and power hand saws (tools and
appliances that require large amounts of
current).
(continued)
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Special Appliance Circuits
• Generally require Number 12 copper
wire with 20 amp overcurrent protection.
Each of these circuits is capable of
supplying 2400 watts of power.
• Lighting outlets should not be operated
from these circuits.
• The NEC requires at least two special
appliance circuits in the kitchen.
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Individual Appliance Circuits
• Serve single, permanently installed
appliances or equipment.
• Each appliance or piece of equipment
will have its own circuit (refer to Figure
21-9 in the textbook).
• Special plugs are required for larger
users of electricity.
(continued)
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Individual Appliance Circuits
• The following appliances commonly have
individual appliance circuits.
– Air conditioner.
– Clothes washer.
– Countertop oven.
– Dishwasher.
– Range.
• Any 120 volt, permanently connected
appliance that is rated over 1400 watts or
starts automatically must also have its own
circuit.
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Circuit Calculations
• Several factors affect the size of the service
entrance and number of branch circuits.
– Size of the house.
– Size and number of appliances.
– Lighting to be installed.
– Planned future expansions.
• Circuit calculations require a series of
calculations.
(continued)
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Circuit Calculations Example
• Size of residence = 1500 square feet.
• Lighting circuits: (3 x 1500 = 4500 watts).
• Special appliance circuits: 2 for kitchen
(120 volts x 20 amp x 2 = 4800 watts).
• Individual appliance circuits: 7 circuits
(totaling 22,000 watts).
• Total = 31,300 watts/240 volts = 130.4
amps. Therefore, this house will require
150 amp service.
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Outlets and Switches
• Outlets, switches,
and conductor joints
must be housed in
an electrical box.
• Lighting fixtures
must be mounted on
a box.
• Common types of
boxes shown.
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Outlets
• Various types of convenience outlets
are available.
• Code requirements affect placement.
• Height of convenience outlets is 12" or
18" above the floor, except in the
kitchen.
• Outlets may be switched for lamps.
• Exterior outlets are weatherproof. Use
one on each side of the structure.
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Types of Outlets
(Leviton Manufacturing Co., Inc.)
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Weatherproof Outlet
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Outlets
• Convenience outlets should be located
in the attic and crawl space.
• “Special outlets” include telephone
jacks, TV antenna outlets, home
entertainment outlets, burglar alarm
systems, and automatic fire alarms.
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Special Residential Outlets
(Leviton Manufacturing Co., Inc.)
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Switches
• Switches should be located in a logical
place 48" above the floor.
• Do not mount behind doors or other
inaccessible locations.
• Bathroom switches should be out of
reach of the tub or shower.
• A switch height of 30" to 40" is preferred
for wheelchair users.
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Residential Switches
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(Leviton Manufacturing Co., Inc.; Broan-NuTone, A Nortek Company)
© Goodheart-Willcox Co., Inc.
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Switches
• Most residential
switches operate
one fixture and are
the single-pole
switch type.
• A three-way switch
allows a fixture to
be switched from
two locations.
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Four-Way Switches
• Switching a light from
multiple locations is
often desirable.
• Fixtures may be
switched from three
locations using two
three-way switches
and one four-way
switch.
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Dimmer Switch
• A dimmer switch is a
special switch used
to adjust the
brightness of a light.
• A regular electrical
box is used to house
the switch.
(Leviton Manufacturing Co., Inc.)
© Goodheart-Willcox Co., Inc.
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Ground-Fault Circuit
Interrupter (GFCI)
• A ground-fault circuit interrupter (GFCI)
is a safety device that continually
monitors the flow of current in a circuit.
• A GFCI responds in 1/30th of a second.
• GFCIs can be placed as any receptacle.
• The NEC defines when and where
GFCIs are used.
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GFCI Protected Outlet
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• Kitchen
GFCI Locations
– All countertop receptacles within 6' of the sink.
• Bathroom
– All receptacles.
• Garage
– All receptacles within reach.
• Outdoors
– All receptacles within 6'-6" of the grade.
• Unfinished basements and crawl spaces
– All receptacles except a dedicated outlet.
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Low Voltage Exterior Lighting
• Low voltage lighting systems are
popular for outdoor use.
• Good outdoor lighting is both functional
and aesthetic.
• A low voltage lighting system consists of
lights, wires, one or more controllers,
and transformers.
• It is more expensive than a 120 volt
system.
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Planning Low Voltage Exterior
Lighting
• Decide where you will need light for
safety, activities, and security.
• Plan for decorative lighting.
• Keep basic considerations in mind.
– Try to avoid glare.
– Locate lights based on their purpose.
Outdoor light fixtures are either decorative
or designed to be hidden.
(continued)
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Planning Low Voltage Exterior
Lighting
– Use shielded fixtures to hide the 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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Decorative Carriage Lamp
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Walkway Lighting
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Exterior Lighting
(Photo courtesy of James Hardie® Siding Products)
© Goodheart-Willcox Co., Inc.
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Low Voltage Wiring
• Low voltage lighting systems are
generally easy to install.
• Keep several points in mind when
installing a system.
– Lights farther away from the transformer
produce less light due to voltage drop.
– Put no more than 100 watts of lighting on
one leg of the tee.
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(continued)
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Low Voltage Wiring
– Choose the proper size transformer.
– Use a GFCI power source for the
transformer.
– Consider an indoor switch and timer.
– Try to prevent corrosion before it starts.
– Call the utility company before digging.
– Leave a little extra wire in the layout.
– Bury the wires at least 6" deep after
checking the setup.
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Low Voltage Wiring
• When installing the lighting system,
divide the circuit into two legs as shown.
This will provide more uniform lighting.
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