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: 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: 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 American Wire Gauge Breaker Breaker Panel Disconnect Switch Distribution Center Fusible Disconnect Switch Fusible Load Center National Electric Code Nonfusible Disconnect Switch

Sizing Wire 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 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 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 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. Disconnect switches are rated 30 amperes, 60 amperes, 100 amperes, 200 amperes, 400 amperes and 600 amperes.

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.