Transcript Chapter 08ACinstallation

Installation of Heating,
Cooling, and Refrigeration
Systems
Electricity for
Refrigeration, Heating and
Air Conditioning 7th Edition
Chapter 8 Installation of Heating, Cooling, and Refrigeration Systems
Installation of Heating, Cooling, and
Refrigeration Systems
Upon completion of this chapter the student will be able
to:
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Understand the standard wire size as defined by the American Wire Gauge
(AWG).
Give the advantages and disadvantages of copper and aluminum
conductors.
Explain the factors that are considered when sizing an electrical circuit
conductor.
Correctly size and install electrical conductors for circuits used in the
industry by the National Electric Code and manufacturers’ instructions.
Calculate the voltage drop in an electric circuit.
Explain the types of enclosures for disconnect switches that are available.
Installation of Heating, Cooling, and
Refrigeration Systems
Upon completion of this chapter the student will be
able to:
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Explain the types, sizes, and enclosures of disconnect switches
that are used in industry.
Explain the types of electrical panels that are used to distribute
electrical power to circuits in the structure.
Install breakers in an electrical breaker panel.
Key Terms
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American Wire Gauge
Breaker
Breaker Panel
Disconnect Switch
Distribution Center
Fusible Disconnect Switch
Fusible Load Center
National Electric Code
Nonfusible Disconnect Switch
Sizing Wire
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The National Electric Code governs the
type and sizes of wire that can be used
for a particular application and a certain
amperage.
Copper is the most popular conductor in
the industry.
Aluminum is used in some cases because
of its low cost.
Copper Wire
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Copper wire bends easily, has good
mechanical strength, resists corrosion,
and can be easily joined together.
Aluminum Wire
• Aluminum is also a good conductor of
electricity, however, Aluminum has a
tendency to corrode.
• Aluminum also has a lower melting point
than copper.
Wire Size
• Standard wire size is defined in the United
Sates by the American Wire Gauge (AWG).
• The American Wire Gauge lists the largest
wire 0000 (4/0), down to number 50, which is
the smallest wire.
• In the industry wire sizes from number 20 to
number 4/0 are most common.
• The most popular sizes are from number 16 to
number 4
Circular Mil System
• Circular mil sizing runs from 250 MCM
(MCM is the abbreviation for 1000 circular
mils), which is about ½ inch in diameter, to
750 MCM, which is about 1 inch in
diameter.
Factors to Consider in
Wiring
• Factors to consider when sizing circuit
conductors include:
• Voltage Drop
• Distance the conductor must be fed
• Insulation Type
• Enclosure
• Safety
Voltage Drop
• Voltage drop in a conductor is of prime importance
when sizing wire.
• If the voltage drop is large enough, it will seriously
affect the operation of the equipment.
• Even a small voltage drop can be detrimental to the
equipment.
• To determine the voltage drop simply measure the
voltage at the equipment when it is in operation and
subtract it from the voltage at the supply.
• The maximum recommended voltage drop for a branch
circuit us 3%.
• The allowable voltage drop of most manufacturers is
10% below the nameplate rating.
Insulation
• The type of insulation surrounding the
conductor usually determines its application
and the amperage it can be used for.
• Insulation can be heat resistant, moisture
resistant, heat and moisture, or oil resistant.
Wire-Sizing Charts
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The wire sizing charts from the NEC are usually accurate for
sizing electric conductors unless the circuit is extremely
long.
For Example:
If a five-ton condenser unit draws 24 amperes, the service
the technician should add 25% of the full-load amperage
to the total, which would be 6 amperes.
This gives a total of 30 amperes for the wire-size data.
Using the wire sizing table the circuit would require a
copper conductor of 10TW copper wire or a 8TW
aluminum conductor.
Calculating Voltage Drop
• To calculate the voltage drop in a conductor,
you must know the number of feet of wire
that is used.
• Once the distance has been determined
Ohms Law can be used to determine the
voltage drop.
Disconnect Switches
• All heating, cooling and refrigeration equipment should
have some means for disconnecting the power supply
at the equipment.
• The neutral conductor, if present, must not be
disconnected by this device.
• A disconnect switch is a two- or three-pole switch
mounted in ab enclosure
• The switch can be purchased with or without a space
for fuses.
• Using fuses provide over-current protection for the
conductors and equipment.
• Disconnect switches can be purchased for general
duty or heavy duty.
• Heavy-duty disconnect switches would be installed for
equipment requiring frequent switching.
Enclosures
• The types of enclosure that the disconnect
switch mounts in is determined by the
conditions existing in the area of installation.
• A general type of enclosure could only be
used where there were no problems of
moisture, dust, or explosive fumes.
• A rain-tight disconnect enclosure could be
used in areas of moisture but not where dust
or explosive fumes exists.
• An explosion-proof enclosure could be used in
any locations
Fusible and Non-fusible Switches
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If the only purpose of a disconnect switch is to break the
power supply, then a non-fusible disconnect switch should be
used.
But if a means of protection for the wire or equipment is
needed, a fusible disconnect switch should be used with the
proper fuse size.
The selection of a fusible disconnect switch is determined
by duty, enclosure type and size.
• Fuses are designed so that one size covers several different
ampacities.
• The same size fuse can be purchased to cover from 1 to 30
amps, from 30 – 60 amps, from 70 – 100 amps, and from 100 –
200 amps.
Fusible Load Centers
• Fusible load centers or breaker panels are
electric panels that supply the circuits in
the structure with power and protect those
circuits with fuses.
• Air-conditioning technicians often find
themselves working on fusible load
centers when the owner of an older home
decides to have air conditioning installed.
Breaker Panels
• Breakers are devices that detect any
overload above their rating in a circuit and
open the circuit automatically.
• The breaker must then be reset manually.
• Breakers are made with one, two or three
poles.
• The poles denotes how many hot legs are
being fed from the breaker to the appliance.
• A one-pole breaker supplies one hot leg and
makes up a 120-volt-single-phase circuit.
• A two-pole breaker supplies two hot legs and
make a 240-volt-single-phase circuit.
Construction
• Breaker panels are built in several different forms
• The breaker from different manufacturers do not
usually fit each others’ panels.
• A main breaker provides a main switch in the panel
and addes a means of overload protection for the
entire panel.
• A breaker panel can be obtained with main lugs and
no main breaker.
• Breaker panels are rated by how many amps the
main lugs can carry and by the rating of the main
breaker.
• Breaker panels are built for use with single-phase
or three-phase systems and for 250 volts or 600
volts.
Installation
• The installation of a breaker into a breaker
panel causes little or no trouble.
• Before installing a breaker in a panel, you
should cut off the power supply to the panel.
Distribution Centers
• Distribution centers are designed to
distribute the electrical supply to several
places in a large structure.
• Their use in largely confined to commercial
and industrial applications.