 Preface
This is a concise, practical, and useful guide designed for easy reference by anyone involved with electrical systems for heating, ventilating, refrigeration, and air-conditioning. Users of this manual will save time and money by applying its information to everyday jobs.
Each chapter covers its topics in great practical detail. The user of the manual is given specific hands-on tips which help the reader perform a given task better and more efficiently. There is no other work that gives such carefully detailed directions and hints for those involved in HVAC electrical systems.
A large number of tables and illustrations help the reader do more in less time. These tables and illustrations give actual usable data for direct application to specific HVAC electrical problems. Thus, the user can keep this manual alongside a desk, drafting table, or on the job for constant reference. Such a reference work has long been needed for the practical HVAC technician working with electrical systems.
Practical data from electrical manufacturers is included in many of the tables and illustrations. Since the manufacturers of electrical components and equipment know the specifications and capabilities of their products better than anyone else, this information is most valuable to electrical technicians.
The author hopes that every user of this manual finds ideas, tips, or methods that will help on the job. To get the most from this manual, make a habit of referring to it whenever a question arises about a method or technique. You will find this manual a constant source of useful information.
JOHN E. TRAISTER
Chapter One
The Electrical System
Electricity has become such an integral part of our daily lives that we take it for granted. Then one day the heating or cooling system stops without warning, or we throw a switch or activate a control and nothing happens-that vital electrical service has been interrupted. The reason for this interruption may include faulty equipment, components, or wiring, but the reason may very well be a power outage.
What causes outages? It is helpful in answering this question to compare the flow of electricity in a wire or conductor to the flow of water in a pipe. A break in a water pipe will cut off the flow of water. Similarly, a break in the wires, or in any of the components that constitute the electrical system, causes an interruption in electricity flow. Faulty electrical components are also quite common in heating, ventilating, and air-conditioning (HVAC) systems.
An overall understanding of the nature of electricity and of the system that produces it is the best foundation for understanding electrical problems in HVAC systems.
The essential elements of an electrical system capable of producing power to operate HVAC systems include generating stations, transformers, substations, transmission lines, and distribution lines. The drawing in Fig. 1-1 shows these elements and their relationships.
ELECTRICITY AND ITS GENERATION
Electricity is the flow of electrons, tiny atomic particles. These particles are found in all atoms. Atoms of some metals such as copper and aluminum have electrons which are easily pushed and guided into a stream. When a coil of metal wire is turned near a magnet, or vice versa, electricity will flow in the wire.
This principle is made use of in generating plants: water or steam is used to turn turbines which rotate electromagnets that are surrounded by huge coils of wire. The push transmitted to the electrons by the turbine/magnet setup is measured in units called volts. The quantity of the flow of electricity is called curren4 and it is measured in amperes or "amps."
Multiply volts by amps and the result is watts- the amount of work the electricity can do. Electrical appliances and motors have certain watt requirements depending on the task they are expected to perform. When speaking of requirements for large HVAC systems, the term kilowatts (1 kilowatt equals 1000 watts) is used. This term is also used when speaking of power production or power needs. An electrical power plant produces kilowatts, and power companies sell power in units called kilowatt-hours. For example, a small 100-watt fan motor operated for 10 hours uses 1 kilowatt-hour of electricity (100 x 10 = 1000 watts or 1 kilowatt-hour).
Electricity is produced at the generating plant at voltages varying from 2400 volts to 13,200 volts. Transformers are also located at the generating plant to step up the voltage to hundreds of thousands of volts for transmissions kind of wholesale block technique for economically moving large amounts of power from the generation point to key locations.
Electricity is transported from one part of the system to another by metal conductors, cables made up of many strands of wire. A continuous system of conductors through which electricity flows is called a circuit.
TRANSMISSION
The system for moving high-voltage electricity is called transmission system. Transmission lines are interconnected to form a network of lines. Should one line fail, another will take over the load. Such interconnections provide a reliable system for transporting power from generating plants to communities.
Most transmission lines installed by power companies utilize three-phase current-three separate streams of electricity, traveling on separate conductors. This is an efficient way to transport large quantities of electricity. At various points along the way, transformers step down the transmission voltage at facilities known as substations.
Substations can be small buildings or fenced-in yards containing switches, transformers, and other electrical equipment and structures. Substations are convenient places to monitor the system and adjust circuits. Devices called regulators, which maintain system voltage as the demand for electricity changes, are also installed in substations. Another device, which momentarily stores energy, is called a capacitor, and is sometimes installed in substations; this device reduces energy losses and improves voltage regulation. Within the substation, rigid tubular or rectangular bars, called busbars or buses, are used as conductors.
At the substation, the transmission voltage is stepped down to voltages below 69,000 volts which feed into the distribution system.
DISTRIBUTION
The distribution system delivers electrical energy to user's energy-consuming equipment-such as lighting, motors, and of course, HVAC equipment.
Conductors called feeders, radiating in all directions from the substation, carry the power from the substation to various distribution centers. At key locations in the distribution system, the voltage is stepped down by transformers to the level needed by the customer. Distribution conductors on the high-voltage side of a transformer are called primary conductors (primaries); those on the low-voltage side are called secondary conductors (secondaries).
Transformers are smaller versions of substation regulators and capacitors are installed on poles throughout the distribution system.
Distribution lines carry either three-phase or single-phase current. Single-phase power is normally used for residential and small commercial occupancies, while three-phase power serves most of the other users.
UNDERGROUND INSTALLATIONS
Most power companies now utilize transmission systems that include both overhead and underground installations. In general, the terms and the devices are the same for both. In the case of the underground system, distribution transformers are installed at or below ground level. Those mounted on concrete slabs are called pad mounts (see Fig. 1-2), while those installed in underground vaults are called submersibles. Buried conductors (cables) are insulated to protect them from soil chemicals and moisture. Many overhead conductors do not require such protective insulation.
Figure 1-2
Pad-mount transformers
When underground transmission or distribution cables terminate and connect with overhead conductors at buses or on the tops of poles, special devices called potheads or cable terminators are employed. These devices prevent moisture from entering the insulation of the cable and also serve to separate the conductors sufficiently to prevent arcing between them. The cable installation along the length of the pole is known as the cable riser.
SECONDARY SYSTEMS
From a practical standpoint, those involved with HVAC electrical systems need only be concerned with the power supply on the secondary (usage) side of the transformer, as this determines the characteristic of the power supply for use in the building or on the premises.
Two general arrangements of transformers and secondaries are in common use. The first arrangement is the sectional form, in which a unit of load, such as one city street or city block, is served by a fixed length of secondary conductors, with the transformer located in the middle. The second arrangement is the continuous form in which the secondary is installed in one long continuous run, with transformers spaced along it at the most suitable points. As the load grows or shifts, the transformers spaced along it can be moved or rearranged, if desired. In sectional arrangement, such a load can be cared for only by changing to a larger size of transformer or installing an additional unit in the same section.
One of the greatest advantages of the secondary bank is that the starting currents of motors, many of which are used in HVAC systems, are divided among transformers, reducing voltage drop and also diminishing the resulting lamp flicker at the various outlets.
Power companies all over the United States and Canada are now trying to incorporate networks into their secondary power systems, especially in areas where a high degree of service reliability is necessary. Around cities and industrial applications, most secondary circuits are three-phase-either 120/208 V or 480/208 V-and wye-connected. Usually, two to four primary feeders are run into the area, and transformers are connected alternately to them, The feeders are interconnected in a grid, or network, so that if any feeder goes out of service, the load is still carried by the remaining feeders.
The primary feeders supplying networks are run from substations at the usual primary voltage for the system, such as 4160, 4800, 6900, 13,200 volts. Higher voltages are practicable if the loads are large enough to warrant them.
COMMON POWER SUPPLIES
The most common power supply used for residential and small commercial applications is the 120/240-volt, single-phase service; it is used primarily for light and power, including single-phase motors up to about 7-1/2 horsepower (hp). A diagram of this service is shown in Fig. 1-3.
Figure 1-3
Single-phase, 3-wire, 120/240-volt wye electric service
 Four-wire delta-connected secondaries (Fig. 1-4) and 4-wire, wye-connected secondaries (Fig. 1-5) are common around industrial and large commercial applications.
It should be remembered that the characteristics of the electric service and the HVAC equipment must match; also, the characteristics of an electric service will often dictate those for the HVAC equipment, or vice versa.
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