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BASIC ELECTRICAL WIRING SKILLS

8602-A

ELECTRICAL PRINCIPLES, TERMINOLOGY, AND SAFETY

The use of electricity is so common that most people assume that it will always be available on demand. Tofully realize the dependence upon electricity, survey the ways electricity is being used each day in the homeand on the farm and ranch. Electricity is doing more to increase work efficiency and promote enjoyable livingthan any other single factor. The use of electricity has grown to the extent that an increasing portion of thehome or business budget is used in paying for this source of energy.

DEFINITION OF ELECTRICITY

Electricity* can be defined in several ways. The layman defines electricity as a form of energy that can beconverted to light, heat, sound, and motion. Electrical engineers define electricity as the flow of electronsfrom one atom to another. This flow of electrons is controlled in an electric circuit. The amount of energyproduced depends on the number of electrons in motion.

To better understand how electricity works, it is necessary to understand the basics of an atom. The centerof an atom, or nucleus, contains positively charged protons. In an electrically neutral or “balanced” state,each atom has an equal number of electrons and protons. The electrons are arranged in orbital layersaround the nucleus with a negative charge. A hydrogen atom, for example, contains one proton and oneelectron. Electrons can be forced to leave their outer orbital layer and attach to the outer ring of anadjacent atom. When extra electrons are attached to an atom they become negatively charged, while theatom that gives up the electron has become positively charged.

* Underlined words are defined in the Glossary of Terms.

Another example is the copper atom that has 29 protons in the nucleusand 29 electrons in the orbiting layers around the nucleus. However,the electrons in outer orbit in a copper atom are loosely held, facilitatingthe exchange of electrons between copper atoms. Even thoughelectrons have been exchanged, the atoms are still balanced. Eachatom of copper has the same number of protons and electrons.Because electrons are loosely held in a copper atom allowing for theexchange of electrons, copper is a good conductor of electricity, whilehydrogen is a good insulator.

THE GENERATION, TRANSFORMATION, AND DISTRIBUTION OF ELECTRICITY

How Electricity is Generated

Electricity is produced from generators that are run by water, steam, or other energy forms. If water is usedas a source of power to turn generators, it is referred to as hydroelectric generation. There are a number ofthese type located in areas where large dams have been built across large streams. In Texas, versus other

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states, less than 5% of electricity is produced hydroelectrically. Waterpower uses the same principle of theancient “water wheel.” The water wheel called a “turbine wheel” is constructed of metal and has an electricgenerator attached to the turbine shaft. Water flows against the turbine blades turning the turbine and thegenerator. Coils of wire inside the generator are turned through a magnetic field allowing electrons to flowalong a conductor from the generating site.

Steam power produces approximately 85% of all electricity used in the United States. Water is heated in aboiler converting liquid to steam. Steam, at high temperatures and pressures, causes the blades to rotate theturbine. The electric generator turns with the turbine generating electricity. These are also referred to asthermal-powered generators. Heat for producing steam is supplied from fossil fuels, nuclear fission, biomass,wood, wind, and geothermal. There is an increasing interest in these areas.

How Electricity is Distributed

Electric energy produced in generating plants is transported from the plant to the consumer in wire linesknown as transmission or distribution lines. Generators at the power plant typically generate 15,000 volts ofelectricity. From the power plant, electricity is carried to a step-up transformer, which increases the voltagefrom 69,000 to 750,000 volts. This increase in voltage is necessary to move large quantities of electricityover long distances through transmission lines from the step-up substation to the distribution area. As theelectric power nears the point of usage, transmission voltage is reduced by a step-down transformer thatreduces the voltage to 7,200 to 14,000 volts for distribution to customers or consumers and is carriedthrough distribution lines. Transformers at the business or residence, further reduce the voltage to 120 or 240volts at the meter of the customer.

How Transformers Work

As previously mentioned, transformers are devices used to increase or decrease the amount of voltage.When the voltage is increased or stepped up, the amperage is reduced proportionately. If the voltage isdecreased or stepped down, the amperage must also be increased. A basic transformer consists of two coils(windings), a primary coil and a secondary coil. These coils of wire are wound around an iron core. One coilhas more windings than the other does. Transformers use these coils and the iron core to transform electricalenergy into magnetic energy, and then back into electrical energy again.

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With a step-up transformer, the power source (powerplant) is connected to the coil with the fewest numberof turns, and is referred to as the primary coil. Electricityis increased through induction in the secondary coil.This increase in voltage is due to the greater number ofturns in the secondary coil in a step-up transformer.

In a step-down transformer, the power source(transmission lines) is connected to the primary coil.The power from the secondary coil is lower in voltage.

HOW ELECTRICAL ENERGY MOVESTHROUGH A CIRCUIT

The path through which an electrical current flows iscalled a circuit. A current is the movement of electronsthrough an electrical conductor. Generators produceand release current the moment it is needed. Thecomplete electrical pathway from the power source through the load and back to the source is known as aclosed circuit. As long as electrical equipment is turned on and the circuit is completed or closed, there is acontinuous flow of current. If the electrical pathway is not complete the circuit is said to be an open circuit.For example, when electrical equipment is turned off, the circuit is opened and electron flow stops.

The electrical circuit is made up of both a hot and a neutral wire. Both wires are needed to provide one wireover which electrons leave the source of power toward the load and one on which they can return from theload to the power source. A load is any device that converts electrical energy back into another form ofuseable energy. For example, a light bulb converts electrical energy into light and heat.

Hot wire – A conductor that carries electrical pressure to the load. They will show voltage when measuredwith a voltmeter. (Color Code: usually black or red)

Neutral wire – A conductor that carries current from the load back to the source. Neutral conductors arenot under electrical pressure, or zero voltage. (Color Code: usually white)

Ground wire – The conducting wire that transmits electrical current to the earth to minimize the dangerfrom electrical shock. (Color Code: can be green or bare wire)

These wires are usually made of copper because copper is a good conductor or carrier of electricity. Aconductor is any material that allows electrons to move readily offering low resistance. The best conductorsare gold, silver, copper, aluminum, and bronze, respectively. Because of the expense of gold and silver,copper is commonly used. Copper and aluminum should not be spliced together due to their incompatibilityresulting in deterioration and oxidation.

An insulator is a material that will not conduct electricity because it will not release its own electrons. Materialssuch as glass, paraffin, porcelain, rubber, silk, cotton, dry wood, and most plastics are used as insulators.

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HOW ELECTRIC ENERGY IS MEASURED

Electric Current

The generator or other device used to produce the electrical energy is similar to a pump used to force waterthrough pipes. The flow of water is measured in gallons per minute. Similarly, the flow of electrical current ismeasured in amperes, abbreviated as “A”or “I” (Intensity of current). It may be referred to as amperage(or amp), which is the rate at which electric current flows through a conductor per second. One amp ofcurrent is approximately 6,280,000,000,000,000,000 electrons passing any particular point in a conductorper second. An instrument called an ammeter is used to measure this electrical current flow. Current mustactually pass through the meter to measure the current. If no current is flowing, the ammeter measures “0.”

Electric Pressure

The volt, abbreviated as “V” or “E” (Electromotive Force), is the unit of measure of electrical pressure or thepressure being applied to force electrons through a circuit. Voltage may be compared with water pressure inpounds per square inch in a water system. This pressure is available in energized circuits all the time whetherelectrical equipment is being used or not.

Common service voltages are 120 volts and 240 volts. The 120-volt circuits have one hot wire and oneneutral wire. Circuits used for lighting and small appliance are typically supplied with 115 to 120 volts. Largerequipment such as heating and air-conditioning appliances, welders, and 1/2 horsepower motors or larger use240 volts. The 240-volt circuits have two hot wires and one neutral wire. If there are three wires, both 120Vand 240V service is available. Some motors are designed for dual-voltage and can be connected for use with120 or 240 volts, but not at the same time.

Volts can be measured with a voltmeter. The voltage in a 120-volt circuit can be measured by fastening onelead from the voltmeter on the hot terminal and the other on the neutral. The voltage on a 240-volt circuit canbe measured by fastening a lead on the voltmeter to each of the hot wires. This is because each hot wire in240-volt circuits is one-half the total voltage.

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Some voltage may be used trying to overcome the resistance in the conductors. This can happen when anappliance that requires a lot of current is started. This reduction in voltage is referred to as voltage drop.Factors that influence voltage drop are size of wire, length of wire, and the number of amps flowing. A dropin voltage may cause a loss of heat, light, or power output of a motor. It could cause motor burnout unless themotor is properly protected with items such as a time-delay fuse.

Electric Power

Electric power is measured in watts, abbreviated as W. It may be referred to as wattage. When applied toelectrical equipment, it is the rate that electrical energy is transformed into some other form of energy such aslight. Watts may be compared to the work done by water in washing a car. Keep in mind that amperes arecurrent flow and volts are the electrical pressure. Neither amperes nor volts by themselves give a measure ofthe amount of power produced for turning motors or producing heat or light. For example, if 15,000 voltswere available but no free electron flow or amps, there would be no power. Also, if there were enough freeelectrons in a circuit to provide a flow of 3,000 amperes but no volts or pressure, there would be no powerto make them flow. The following relationship exists among amperes, volts, and watts:

Watts = Volts x AmperesVolts = Watts/AmperesAmperes = Watts/Volts

For example, if a 100-watt light bulb operates at 120 volts, it will draw .833 amperes of electricity.

Amperes = 100 watts/120 volts= .833 amperes

Equipment of more than 1,000 watts is often rated in kilowatts. A kilowatt (kW) is 1,000 watts. Kilowattsare used in computing electrical energy consumed. Kilowatts are determined by dividing the number of wattsby 1,000 (1 kW = 1,000 W).

Most electrical equipment is rated in watts. However, most electric motors are measured in horsepower.Horsepower (hp) is the unit of mechanical power equal to 746 watts of electrical power (assuming 74.6%electric motor efficiency). One hp and above motors are rated at 1,000 watts per hp; motors below one hpare rated at 1,200 watts per hp.

Resistance

Resistance is any material that opposes the flow of electricity. All materials, even good conductors, havesome resistance to the flow of electrons. Conductors have very low resistances, while insulators have veryhigh resistances. The unit of measure of electrical resistance is known as an ohm (abbreviated as “R” forresistance). The amount of resistance (ohm) in a conductor is determined by:

1. The material of which the conductor is made2. The size of the conductor3. The length of the conductor

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Resistance is proportional to length and size of the conductor. If the length of wire is doubled, the resistanceis doubled. If the diameter wire is reduced by half, then the resistance is doubled. The relationship betweenamps (electric current), volts (electromotive force), and resistance is called Ohm’s law. Ohm’s law statesthat volts are equal to amperes times resistance.

E = I x R

E = VoltsI = AmperesR= Resistance

The Ohm’s law equation can be rearranged to solve for any of thethree values as long as the other two values are known. For example,the resistance in a 6-volt circuit, if 2 amperes of current are flowing inthe circuit is 3 ohms. The formula can be rearranged as shown belowto provide the answer.

R = E/IR = 6 volts/2 amperesR = 3 ohms

If voltage and resistance are known, the Ohm’s law equation can alsobe rearranged to solve for amperes. A 240-volt circuit containing atotal resistance of 45 ohms will have 5.33 amps flowing in it.

I = E/RI = 240 volts/45 ohmsI = 5.33 amperes

Devices called multimeters are capable of measuring voltage,resistance, and current flow in milliamperes and are commonly calleda volt-ohm-milliammeters (VOM).

COMPUTING ELECTRICAL ENERGY USE AND COST

Electrical energy is normally measured and purchased in kilowatt-hours (kWh). A watt-hour is the use of 1watt for 1 hour. A kilowatt-hour is the use of 1,000 watts for 1 hour. The following formulas should be usedfor determining watt-hours, kilowatt-hours, and cost.

Watt-hours = Watts x hours of operationKilowatt-hours = Watt-hour/1,000Cost = kWh x local rate per kWh

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Example cost problem using the Watts and Time Estimate method: The nameplate data from an appliance indicates that it properly operates at 120 volts and 5 amps. The motor’s monthly hours of operation are 10 hours and the local rate per kWh used is 8 cents. The estimated cost of operation per month would be calculated as follows: Step 1) Watts = Volts x Amperes Step 3) kWh = Watt-hours/1000 = 120 x 5 = 6000/1000 = 600 = 6 Step 2) Watt-hours = Watts x hours Step 4) Cost = kWh x rate = 600 x 10 = 6 x 8 = 6000 = 48 cents

TYPES OF CIRCUITS

There are two basic types of circuits: series and parallel. A third type is a series-parallel. A series-parallelcircuit is a network of circuits that incorporates both series and parallel circuits.

In a series circuit all the current must flow through each device in the circuit. The current in a seriescircuit has only one path to flow. Removing or opening any one device in the series circuit will stop the flowof current for the whole circuit. The same current or amperage flows through each load in a series circuit.However, the voltage is equal to the individual voltage drops from the each load. Switches, fuses, andcircuit breakers are always connected in series.

A parallel circuit has separate paths for the current to flow through. Parallel circuits provide the samevoltage across each load (lights or appliances). Removing one device in the parallel circuit has no effecton the other devices in the circuit. The current flow is divided through each load on the circuit and isequal to the total current from the source. In most cases, except for some Christmas tree lights, appliancesand lights are connected in parallel.

TYPES OF ELECTRIC CURRENT

Electrons in a conductor can move continuously in the same direction, or they can change directions backand forth. When electrons always flow in one direction the current is called direct current (DC). Electricityfrom dry cell batteries and batteries used in automobiles and tractors is direct current.

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When electrons move back and forth, reversing their direction regularly, the current is called alternatingcurrent. Electricity that flows through lights, refrigerators, and other home equipment is alternating current.Alternating currents change direction of flow several times per second, depending on the direction the voltageforces it. Electric utilities produce alternating current.

The flow of electricity with voltage fluctuation is called a cycle. Electricity in AC flows in one direction forone-half cycle, and then reverses direction and flows in the other direction for one-half cycle. The term forthe cycles per second is hertz (Hz). The power suppliers in the U.S. control the power to 60 hertz. Thiscauses electric clocks to keep accurate time because most operate on 60 cycles. If the number of cyclesper second were increased or decreased, clocks would gain or lose time. European power is on differentcycles. For this reason, travelers normally purchase converters for their personal electric appliances suchas computers, electric razors, hair dryers, etc.

TYPES OF ELECTRIC POWER

Single-phase service is the most common type of electrical service or power available to consumers. Onetransformer is used between the distribution line and the meter. Usually three wires, two “hot” and oneneutral, are installed to provide 120V and 240V single-phase service. Single-phase service may also besupplied with three-phase service.

Three-phase service is designed especially for large electrical loads. Three-phase service is more expensivedue to installation of four wires and three transformers. Three wires are “hot” and one is neutral. With three-phase power, the total electrical load can be divided among the three phases, requiring smaller wires andtransformers.

CIRCUIT FAILURES

There are many types of conditions that can cause a circuit to fail, such as open circuits, overloads, shortcircuits, and ground faults. An open circuit is a break or interruption in the electrical pathway that stops thecurrent flow. Tuning off the switch for a light is one example of an open circuit. Many times open circuits areunintentional resulting from damage to the equipment or conductor, such as cutting the wire.

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An overload occurs whenever excess current flows through a circuit. An example of this unsafe current flowmay be plugging too many products into a circuit. Another example would be using an extension cord that israted 15 amps to supply electricity to a 20-amp load. The load(s) require the use of more amps than thecircuit can safely supply. Circuit overloads are dangerous and can cause shock or a fire.

A short circuit occurs when current flows in an unintended path. This unintended path usually offers a lowerresistance path for the current to follow, bypassing the normal circuit load(s). Short circuits result from aninsulation breakdown or a direct connection between conductors. An example of a short circuit conditionmay be when a drill fails to work because wires in the cord are in direct contact with one another. The currentbypasses the drill, failing to flow through the motor windings and follows the path of lower resistance back tothe source. Short circuits are extremely dangerous.

CIRCUIT PROTECTION DEVICES

Fuses and Circuit Breakers

Fuses and circuit breakers are used to protect electrical equipment and wiring from overloads. When anoverload occurs the circuit breaker trips or the fuse melts inside to prevent the wiring from overheating andcausing a fire.

Fuses contain a link made from a low-melting alloy that is designed to carry current up to the rating of thefuse. The link melts when the current exceeds the amperage rating of the fuse opening the circuit andstopping the flow of electricity. Fusetrons (time-delay) and fustats (two-part time-delay) are two commonfuses. A time-delay fuse has the ability to carry a temporary overload of current for a short durationwithout disengaging the contacts or melting the fuse link, such as the overload caused by the starting of anelectric motor. Fuses are of two basic types, plug and cartridge. Fuses must be replaced once the linkmelts or blows inside the fuse.

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Circuit breakers eliminate the replacement of fuses and are commonly used even though a circuit breaker boxcosts more than a fuse box. Circuit breakers are of two types, thermal and magnetic. The thermal breakerhas two contacts held together by a bi-metal latch. An overload of current causes the bi-metal strip to heatand expand; the latch releases, and the points spring open. After the bi-metal strip cools; the switch is reset;and service is restored.

The magnetic breaker has contacts that are held together by a latch, which is released by the action of anelectromagnet. The amount of current flowing through the circuit will determine the size of the electromagnet.Moving the toggle switch to the “on” position resets this type of breaker.

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Ground Fault Circuit Interrupters

Ground fault circuit interrupters (GFCI) are designed to protect humans, equipment, and/or electrical systemsfrom injury or damage if electricity flows in an unintended path (a short). A GFCI is a very sensitive devicethat compares the current flowing out from the source through the hot wire of a circuit with that returningback to the source through the neutral wire. If one wire is carrying less current than the other, a conditionknown as a ground-fault has occurred. In a ground fault, some of the current may take an alternate path backto the source, possibly through the ground wire or through a person.

A difference in current flow as little as 5 milliamperes (mA) or greater will cause the GFCI to open the circuit,shutting off the power and eliminating any shock hazard. A current flow as little as 10 mA through the humanbody may be fatal under certain circumstances. Once the source of load imbalance has been identified andcorrected, the GFCI may be reset and tested as shown below.

Current flow from a ground-fault may or may not trip a circuit breaker or blow a fuse to provide a personprotection against shock, unless the current exceeds the amperage rating. If the circuit breaker or fuse doesnot trip, the individual may still become electrocuted. However, there are some GFCI breakers that willprovide protection for everything on the circuit.

The National Electrical Code (NEC) requires GFCIs for all 120V, single-phase, 15 and 20 amp receptaclesinstalled outdoors, in bathrooms, and in garages for residential buildings. A GFCI is required at constructionsites and some other applications. A variety of GFCI equipment is made for 120 and 240-volt circuits. SomeGFCIs are available as portable.

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ELECTRICAL SAFETY

Organizations

There are many agencies and organizations that have been established to help ensure the safe use of electricity.Two organizations that have an important role in electrical safety codes and regulations are the National FireProtection Association (NFPA) and the Underwriters’ Laboratory (UL). Both are nonprofit organizations.

The National Fire Protection Association (NFPA) is devoted to promoting and improving the science andmethods of fire protection. The NFPA publishes the National Electric Code (NEC). The NEC serves as anational standard for safe installation of electrical wiring and devices that is revised every three years. However,the NEC is not law. All wiring should meet the requirements of the NEC as well as local building codes.

The Underwriters’ Laboratory (UL) provides voluntary product testing of all types of wiring materials andelectrical devices to determine if they operate safely and prevent electrical shock and/or fire.

Safety Precautions

Many safety measures may be taken to prevent injuries when working with electricity. Listed below are a fewelectrical safety rules.

Wear appropriate clothing. Clothing should be made of materials low in flammability.

Wear boots or shoes with rubber heels or soles to insulate against shock.

Ground all outlets, service entrances, light fixtures, etc. Current that has taken an alternate path willflow toward the ground through grounding wires or a “person.” Use GFCIs whenever possible toprotect against electrical shock.

Inspect all electrical equipment and devices to ensure there is no damage or exposed wires that maycause a fire or shock.

Avoid using electric equipment near wet, damp areas.

Always disconnect the power at the service entrance before you begin work by turning the circuitbreaker to the “off” position.

Always use the correct sizes of fuses and circuit breakers. When replacing a fuse or circuit breaker,ensure that the replacement is not rated a larger amperage than the one being replaced.

Always be sure electric motors are rated at an amperage that the power source can carry. Theelectric motor will overload if it is rated at a lower amperage than the power source.

If someone is undergoing electrical shock, do not attempt to grab and pull them free; by doing so, you willbecome part of the circuit. Locate the switch, circuit breaker, or electrical outlet and disconnect and turn offthe source of power as quickly as possible. It is possible to use a dry board or a thick dry piece of rubber orplastic to push or pull the hot conductor from the victim.

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In the case of an electrical fire, use only extinguishers that are approved for electrical fires. A type C fireextinguisher can be used on electrical fires. Refer to IMS catalog # 8600 for the classes of fires andextinguishers. For more information on electrical safety and electricity, visit Web sites such as:

http://www.osha-slc.gov/OshStd_toc/OSHA_Std_toc_1910_SUBPART_S.htmlhttp://www.nesf.orghttp://www.electrical-safety.comhttp://www.cdc.gov/niosh/nasd/menus/topelect.htmlhttp://www.nfpa.org/Home/index.asp

(For electricity activities related to your SAEP, refer to IMS # RB-221, Activities for Agricultural Science221. After completing an activity, be sure to record the entry in the journal page of your Internet recordbook, and click on 221-E for the Course and Unit of Instructions.)

Acknowledgements

Shannon Houy, Graduate Assistant, Department of Agricultural Education,Texas A&M University, researched and developed this topic.

Kirk Edney, Curriculum Specialist, Instructional Materials Service,Texas A&M University, reviewed this topic.

Vickie Marriott, Office Software Associate, Instructional Materials Service,Texas A&M University, prepared the layout and design for this topic.

Christine Stetter, Artist, Instructional Materials Service,Texas A&M University, prepared the illustrations for this topic.

REFERENCES

Buriak, Philip and Edward W. Osborne. Physical Science Applications in Agriculture. Danville, IL:Interstate Publishers, Inc., 1996.

Duncan, Ralph and James E. Wren. Electrical Wiring. 7th ed. Winterville, GA: AAVIM, 1999.

Johnson, Donald M., Joe Harper, David E. Lawver, and Philip Buriak. Mechanical Technology inAgriculture. Danville, IL: Interstate Publishers, Inc., 1998.

Herren, Ray V. and Elmer L. Cooper. Agricultural Mechanics: Fundamentals and Applications. 4thed. Albany, NY: Delmar Publishers, Inc., 2002.

Maton, Anthea, Jean Hopkins, Susan Johnson, David LaHart, Maryanna Quon Warner, and Jill D. Wright.Exploring Physical Science, Texas Edition. Upper Saddle River, NJ: Prentice Hall, 1997.

Rasdall, Joyce O. and George W. Smith, Jr. Understanding Electricity. Winterville, GA: AAVIM, 1998.

Titus, Patricia A., James E. Titus, John Traister. Illustrated Dictionary for Electrical Workers. 2nd ed.Albany, NY: Delmar Publishers, Inc., 2002.

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GLOSSARY OF TERMS

Conductor – A material, typically metal, that allows electrons to move readily offering low resistance.

Distribution lines – Electric lines that deliver the electricity form a step-down distribution transformer tothe final step-down transformer at the customer’s premises.

Electricity – The flow of electrons from one atom to another.

Ground-fault – A dangerous electrical condition where electrical current has taken an alternate path backto the source causing a loss or leakage of current, resulting in one wire (conductor) carrying lesscurrent then the other.

Hydroelectric generator – Generator powered or turned by the presence of water flowing from a higherlevel to a lower level.

Induction – The production of electric current by the build-up and breakdown of a magnetic field in a coil.

Insulator – Any material that has extremely high resistance to the flow of electrical current.

Milliamperes (mA) – Unit of current flow equal to one one-thousandth (.001) of an ampere.

Step-down transformers – Transformers designed to decrease the voltage and increase the amperage. Thesecondary coil has fewer turns than the primary coil. Therefore, the output voltage will be less thanthe input voltage.

Step-up transformers – Transformers used at the power plant to increase the voltage and decrease theamperage. The secondary coil has more turns than the primary coil. Therefore, the output voltage willbe greater than the input voltage.

Transmission lines – Electric lines used to move large quantities of electricity from the power plant for longdistances to the step-down transformer for distribution.

SELECTED STUDENT ACTIVITIES

MATCHING: Place the term in the left column with its definition in the right column.

____ 1. Horsepower A. Material carrying electricity (usually copper oraluminum)

____ 2. Kilowatt-hour B. Unit of mechanical power equal to 746 watts ofelectrical power

____ 3. Alternating current C. Material that will not conduct electricity____ 4. Direct current D. 1,000 watts____ 5. Kilowatt E. The use of 1,000 watts for 1 hour____ 6. Load F. A device that increases or decreases voltage____ 7. Transformer G. Protective devices used to prevent overloads and

short circuits____ 8. Conductor H. Any device that converts electrical energy back

into another form of useable energy____ 9. Insulator I. Current flowing in one direction____ 10. Circuit breakers and fuses J. Current flowing in alternate directions

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MULTIPLE CHOICE: Place the letter of the correct answer in the space provided at the left of each number.

____ 11. Which of the following is the measurement of the rate of flow of electrical current?a. Ampere c. Wattb. Volt d. Ohm

____ 12. Which of the following is the measure of electrical pressure?a. Ampere c. Wattb. Volt d. Ohm

____ 13. Which of the following is the measure of electrical power?a. Ampere c. Wattb. Volt d. Ohm

____ 14. Which of the following is the measure of electrical resistance?a. Ampere c. Wattb. Volt d. Ohm

____ 15. A ____ increases voltage by having more turns in the secondary coil and fewer turns in theprimary coil.a. Step-down transformer b. Step-up transformer

FILL IN THE BLANK: Complete each statement with the correct word or phrase.

16. ________________ is a form of energy that can be converted into light, heat, sound, and motion.

17. Electricity is produced from generators that are run by ____________, ______________, or otherenergy forms.

18. The path through which electrical current flows is known as a ___________________.

19. A ____________________ is the movement of electrons through an electrical conductor.

20. In a ________________ circuit all the current must flow through each device in the circuit; while a_________________ circuit has separate paths for the current to flow through.

TRUE OR FALSE: Circle the “T” if the statement is true or “F” if it is false.

T F 21. The relationship between amperes, volts and resistance is known as ohms law.T F 22. The voltage of a 240-volt circuit may be measured by connecting the voltmeter to one “hot”

wire and the neutral terminal.T F 23. Removing one device in a series circuit has no effect on the other devices in the circuit.T F 24. Electricity in DC flows in one direction for one-half cycle, then reverses direction and flows in

the other direction for one-half cycle.T F 25. The term for cycles per minute is hertz (Hz).T F 26. An overload occurs when excess current flows in a circuit.T F 27. Circuit breakers must be replaced after the circuit has been overloaded.T F 28. Single phase service is the most common type of electrical service or power available to

consumers.T F 29. Circuit breakers and fuses protect humans, equipment, and/or electrical systems from damage

or injury when electricity flows in an unintended path.T F 30. The National Electrical Code (NEC) is the law for safe installation of electrical wiring and devices.

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PROBLEM SOLVING: Use the space provided to solve each problem.

31. Calculate the watt rating for a portable saw that pulls 10 amps in a 120-volt circuit.____________________________________________________________________________

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32. What is the kilowatt rating in a 220-volt circuit with 75 amps of current?____________________________________________________________________________

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33. Calculate the amperage for 5-200 watt light bulbs in a 120-volt circuit.____________________________________________________________________________

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34. If the 5-200 watt light bulbs in the preceding problem are used continuously for eight hours, at therate of 8 cents per kWh, what is cost of operation?____________________________________________________________________________

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35. Using the Ohm’s law equation, what is the resistance in a 120-volt circuit with 10 amps of current?____________________________________________________________________________

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SHORT ANSWER/LISTING: Answer the following questions or statement in the space provided or onadditional paper.

36. Briefly explain how electricity is transported and distributed from the generating plants to consumers.____________________________________________________________________________

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37. What are the purposes and color codes for the following conductors?Hot wire - ____________________________________________________________________

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Neutral wire - _________________________________________________________________

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Ground wire - _________________________________________________________________

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38. Define the following terms.Short circuit - _________________________________________________________________

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Overload - ____________________________________________________________________

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39. What is a ground fault circuit interrupter and how does it work?____________________________________________________________________________

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40. Explain why some circuit breakers and fuses may not provide a person protection against shock withconditions such as ground-faults.____________________________________________________________________________

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ADVANCED ACTIVITIES

1. How Much Electricity Do You Use?a. For a period of several days, keep a record of every electrical appliance you use and record the

amount of time each is run.b. Write down the power rating for each appliance and chart this information. The power rating

should be marked on the appliance in watts.c. Calculate the amount of electricity in kilowatt-hours that you use each day.d. Determine the cost per kilowatt-hour of electricity in your area. Calculate the cost of the electricity

you use each day.

2. Using an iron core magnet and electrical wire, construct a model transformer. Measure the resultswith a multi-meter and chart the results. Increase or decrease the number of coils (windings) andmeasure again with a multi-meter and chart this information. Compare these results and share withyour class.

3. Construct a simple model of a water power generator.

4. Using a multi-meter, measure different electrical equipment. Make a chart of the results and comparethe differences in voltage, wattage, amperage, and resistance of the equipment.

5. Contact your local electric utility regarding deregulations. For more information on deregulation visitthe following Web site:

http://www.citizen.org/cmep/energy_enviro_nuclear/electricity/deregulation

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- NOTES -

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ALL RIGHTS RESERVED

Reproduction prohibited without written permission.Instructional Materials Service

Texas A&M University2588 TAMUS

College Station, Texas 77843-2588http://www-ims.tamu.edu

2002