Residential Wiring to the 2005 NEC

Be the first to review this product

Regular Price: $31.00

Special Price $15.50

Shows how to install rough and finish wiring in new construction, alterations, and additions. Complete instructions on troubleshooting and repairs.



Every subject is referenced to the most recent National Electrical Code, and there's 22 pages of the most-needed NEC tables to help make your wiring pass inspection – the first time.

Weight 1.1000
ISBN 1-57218-153-2
Page Count 352
Author Jeff Markell
Publisher Craftsman Book Company
Dimensions 5-1/2 x 8-1/2

Shows how to install rough and finish wiring in new construction, alterations, and additions. Complete instructions on troubleshooting and repairs.

Every subject is referenced to the most recent National Electrical Code, and there's 22 pages of the most-needed NEC tables to help make your wiring pass inspection – the first time.

Write Your Own Review

You're reviewing: Residential Wiring to the 2005 NEC

CONTENTS
Prefacev
1Electrical Energy1
Historical Introduction1
The Composition of Matter2
Formation of Molecules4
Static Electricity6
Current Electricity8
Basic Electrical Circuits16
Effects of Electrical Energy20
2Distribution of Alternating Current23
DC Sources23
Magnetic-Mechanical Generation and Alternating Current24
Induction and AC Generation30
Power in an AC Circuit41
Commercial Generation and Distribution of AC Power44
3Tools and Safety45
Conventional Hand Tools45
Electrician's Hand Tools49
Power Tools53
Test Instruments55
Basic Wiring Techniques59
4Conductors65
Wire Materials66
Insulation70
Ampacities73
5Grouped Conductors75
6Electrical Boxes87
Metal Boxes87
Single Gang Boxes88
4 Inch Square Boxes91
Multiple Gang Boxes93
Cut-in Boxes93
Octagon Boxes94
Weatherproof Boxes95
Plastic Boxes98
National Electrical Code Regulations Regarding Boxes100
7Wiring Switch Circuits and Outlets105
Switch Types105
Wiring Switch111
Circuits Outlets125
8Plans129
Types of Plans and their Uses131
Floor Plan Symbols131
Branch Circuits145
Cable Plans162
Wiring Diagrams163
Service Load Computation185
9The Service Entrance191
Overhead Service Entrance191
Underground Services196
Meter Box197
Breaker Boxes200
Grounding200
Sizing202
Grounding Electrode System202
Overcurrent Protective Devices204
10Rough Wiring211
Non-Metallic Cable211
BX Cable-Type AC216
Flexible Metal Conduit - Greenfield218
Liquidtight Flexible Metal Conduit219
Electrical Metallic Tubing - EMT, or Thinwall Conduit220
11Finish Wiring of New Work233
Receptacles233
Switches238
Appliances239
Light Fixtures243
12Additions and Alterations to Old Work249
Concealing Electrical Additions or Alterations255
Exposed Additions and Alterations261
13Troubleshooting and Repairs267
14Supplementary Systems289
Signaling and Warning Systems290
Communications296
Entertainment Systems297
Appendix A National Electrical Code Tables299
Appendix B Building and Floor Plans322
Index340
CELECTRICAL ENERGY
H
A
P
T
E
R
1

In order to understand his work satisfactorily, the electrician needs a modest background as to what electricity is and what can be done with it-at least to the extent that these matters are known at this time. Electricity has always been, and to a considerable extent still is, mysterious since it is an invisible form of energy, but as the reader may have discovered with dismay, it is by no means intangible. This is a practical book on how electrical wiring in a small building should properly be done in accordance with accepted standards of good workmanship, and in accordance with the provisions of the National Electrical Code®*. It is not a treatise on theory, so the discussion of theoretical matters will be kept to a minimum.

Historical Introduction

It might surprise some people to learn that as far back as 600 BC the Greeks were amusing and amazing themselves with elementary uses of static electricity. They had discovered, for example, that a piece of amber rubbed with cloth attracted bits of straw, hair, and the like. Their word for amber was "elektron," which is obviously the root of "electron," "electricity," "electronics," and other words containing "electro."

The ancients also discovered that certain heavy, black stones that were found every so often mysteriously attracted iron. Since they happened to be found fairly frequently in a part of Asia Minor called Magnesia they were called magnets. Naturally all manner of hocus pocus was imagined to explain these curious phenomena, and all the early explanations of which we have records were complete nonsense.

Over many centuries it was observed that various other materials had characteristics similar to amber; they too could be rubbed, and would attract light objects. Scientific thinking developed the theory that the rubbed materials leaked a sort of "fluid" that was the cause of the attraction. This fluid was called electricity. Discontent with one "fluid," thinkers by the 18th Century hypothesized there were two fluids. One was called "vitreous," the other was "resinous." The difference was based on the nature of the substances being rubbed. By the mid-18th Century Ben Franklin went back to the one "fluid" theory. He decided that the two fluids were simply different aspects of the same thing. When an object had too much of this electric fluid it was "positive"; if it had too little, it was "negative," and if it was normal, whatever that meant, it was "neutral." While those in scientific fields were dissatisfied with this theory, it was the only one available until the early 20th Century investigations of the structure of matter began to offer a more satisfactory alternative.

The Composition of Matter

Matter is anything that has mass and occupies space. It exists in three states: solid, such as a rock; liquid, such as water; and gaseous, such as the air around us. By means of variations in temperature and pressure, matter can be changed from one state to another. Remove enough heat from a quantity of water, thus reducing the temperature, and at 32°F it will change in state from liquid to a solid, ice. Take the same quantity of water, and add heat, increasing the temperature. At 212°F it will start to vaporize, changing from a liquid to a gas.

Although a particular type of matter may change state from solid, to liquid, to gaseous, the component building blocks of which it is made remain the same, which leaves the question-of what is matter made? To find out one must divide, and subdivide, and subdivide again in order to arrive at the smallest particle that retains the characteristics of that particular type of matter be it water, steel, or foam plastic. That smallest particle is termed a "molecule." There is a different molecule that corresponds to each different kind of matter. But the molecule is by no means the end of the line. Molecules are composed of yet smaller parts termed atoms. Water, for example, is composed of molecules made of two hydrogen atoms plus one oxygen atom-H2O. All matter, then, consists of the atoms of 100 elements combined in different compounds to form the molecules that distinguish different substances from each other. How atoms accomplish this business of combining into molecules will be discussed after we look more closely at the atom itself.

The atoms that compose molecules are quite complicated structures. Each one seems to be a miniature solar system, consisting of a nucleus surrounded by varying numbers of revolving electrons. The nucleus contains various particles such as protons, neutrons, positrons, neutrinos, mesons, and according to recent theories even a couple odd bits called "quarks" and "charms." We are primarily concerned with the bulk of the nucleus which consists of the protons and neutrons. The number of protons in the nucleus differentiate the atoms of the 100 elements from each other. The number of protons in the nucleus of an atom is its "atomic number." Hydrogen is #1, helium is #2, and so on.

Protons are positively charged, neutrons have no electrical charge, and the orbiting electrons are negatively charged. Since under normal conditions atoms are electrically neutral, an atom of any particular element will contain equal numbers of electrons and protons. The number of neutrons, as well as the various other nuclear components (neutrinos, mesons, etc.), has nothing to do with the electron-proton balance. Hydrogen has no neutrons, while the 92 protons of uranium are out numbered by 146 neutrons.

Curiously, while the magnitude of the opposite electrical charges in electrons and protons is equal to each other the difference in mass between the two is staggering. The mass of a proton is 1840 times that of an electron. A similarity appears between what is observed on a gigantic scale in the solar system, and in miniscule scale in the atom. All but a tiny part of the mass of the solar system is contained in the sun. Similarly all but a tiny part of the mass of an atom is contained in the nucleus.

The planets of the solar system are held in their orbits around the sun by a complex off actors involving the mutual attraction of their gravitational fields, and that of the sun, as well as their masses, and the velocities at which they move. Electrons are held in their orbit around the nucleus by the electrostatic attraction between their negative charges, and the positive charges of the protons in the nucleus, and again a relationship between mass and velocity is involved.

At this point the parallel between the atom and the solar system breaks down. The planets of the solar system each differ greatly from each other as to mass, composition, orbital velocity, and other characteristics. The electrons orbiting the nucleus of an atom do not differ.

In order to maintain the centrifugal force to keep from falling into the nucleus, on the one hand, or spinning away from its nucleus, on the other, the electron must move at a constant speed. Because it has mass, it must also have a level of energy determined by the combination of its mass and its velocity. Only a very limited number of specific energy levels are possible for electrons. There are seven altogether. As an electron can only occupy an orbital path appropriate to its energy level, there are seven possible orbits.

The more complex atoms might have as many as 100 electrons, but since only seven possible energy levels exist, the electrons must group at various appropriate orbit distances from the nucleus (Figure 1-1) forming



"shells" in layers around it. A consistently repeated pattern is found in the formation of these shells. The innermost shell (#1) can hold no more than two electrons. Any number above two starts the second shell. It can hold up to eight. When it is filled the third shell is started.

At this point the picture becomes a bit more complicated. The third shell (#3) can hold up to 18 electrons, however, the outermost shell of any atom regardless of which one, may hold no more than eight. Thus when Shell #3 is the outside one, and has eight electrons the next electron must take up an orbit in shell #4. Only after shell #4 has one or two occupants can the rest of the 18 possible spaces in #3 be filled. By the time shell #4 has eight electrons shell #3 will already have its allotted 18. When #4 is the outermost shell and is holding eight electrons shell #5 starts. Shell #4 can hold 32 electrons. When it has its 32, and shell #5 is up to eight, shell #6 is started. Shell #6 is completed and shell #7 started in a similar manner. With all elements it is the spare electrons of the outer shell, whatever shell number that happens to be, that take part in any of the various chemical and electrical phenomena. These are termed "valence electrons."

Formation of Molecules
Regardless of its shell number the outermost shell of any atom can contain no more than eight valence electrons. Any atom that has all eight is stable and does not normally combine with other atoms. The atoms with valence electrons anywhere between one and seven, trying to attain stability, are candidates for combination with other atoms to form molecules. The process of molecule formation is termed atomic bonding and occurs in any one of three ways: ionic bonding, covalent bonding, or metallic bonding.

Ionic Bonding
An atom by itself will contain matching numbers of electrons and protons which, since they have opposite electrical charges, results in a neutral charge for the atom as a whole. However, this matter of valence electrons gets in the way. An atom with more than four but less than eight valence electrons is unstable. It is looking to obtain whatever number of valence electrons are missing to fill its outer shell to eight. Conversely, an atom with less than four valence electrons is also unstable and willing to unload its excess.

Thus where an atom with one valence electron meets another one with seven, there is a tendency for the one to join the seven, thus stabilizing both atoms. However, in the process something else happens. The atom that lost an electron now has a net positive electrical charge of one. The atom that picked up an electron has also picked up a net negative electrical charge of one. An atom that is no longer electrically neutral but has a net positive or negative charge has become an "ion." Ions with opposite electrical charges are attracted to each other tending to combine via "ionic bonding" to form molecules.

Covalent Bonding
Hydrogen with atomic number 1 has only a single electron in the #1 shell. It is unstable because that shell is incomplete without two electrons. One way it stabilizes is to join with another hydrogen atom (Figure 1-2) to form a hydrogen molecule in which the two component atoms share their two electrons. This is an example of "covalent bonding."

Metallic Bonding
Since it is the most commonly used material for electrical wires, copper is a good example of "metallic bonding." The atom in this case has 29 electrons. Two complete shell #1, another 8 complete shell #2, and the next 18 fill out shell #3. That is a total of 28. The 29th is a lone valence electron in shell #4. This lone electron is loosely held and has a tendency to wander off becoming a "free electron." The copper atom has become a positive ion, and so have a lot of others that have also lost their single



valence electrons. Although like charges repel, the copper ions do not simply fly apart as one might expect. They are immersed in a sort of soup of free electrons. The mutual attraction between the positive copper ions and the negatively charged electron mass around them holds the whole business together by "metallic bonding."

That same soup of free electrons, unattached to specific atoms, flows as an electrical current through a metal when it is connected to a source of electrical pressure. We will measure that pressure in volts and measure the current it creates in amperes.

The more free electrons available in a given material, the more readily they will move in response to a given electrical pressure, and the more free electrons there are in a material, the less "resistance" it will have to the flow of those electrons as electrical current.

Materials containing large numbers of free electrons, and therefore offering little resistance to the flow of electron current, are termed "conductors." Those with very few free electrons will necessarily have a high resistance to the flow of electron current since there are but few available electrons to participate in the process. These materials, due to their high resistance, are good insulators.

Metals in general, because of metallic bonding, have many free electrons and are good conductors. Glass, rubber, wood, cloth, and plastics having few free electrons are good insulators. A few materials exist that fall into the cracks between conductors and insulators. They have some of the characteristics of both, hence are called semiconductors. Silicon and germanium are two. These types of materials are used in various electronic devices, but not directly in building wiring; thus they will not concern us.

Static Electricity
Under normal conditions the atoms of a substance are neutrally charged since the negative charges of the orbiting electrons are exactly balanced by the positive charge of the protons in the nucleus. When two electrically unbalanced atoms bond ionically to form a molecule, the molecule then also becomes neutral since the net positive charge of one atom has been off set by the net negative charge of the other.



However, when some outside influence forces many atoms of a material either to gain or lose an electron that material becomes either negatively or positively charged. This charge collects on the object's surface and tends to stay there until conduced away. The pieces of amber rubbed with cloth by the Greeks in 600 BC were charged in this way (Figure 1-3). When you walk across a thick carpet, and then see a small spark when you touch a door knob, you were charged in the same way. This type of surface charge is called a static charge.

It is interesting to note that one important use of static electricity is to precipitate the particulate matter from exhaust gases of industrial plants (Figure 1-4). As the gases enter the precipitation chamber the dust, soot, and other particles are attracted to a positively charged plate. The moment they touch it, they become positively charged and are strongly repelled, and drop to the bottom of the chamber where the charge is grounded.

While this and a few other constructive uses of static electricity exist, the static form is generally useless because it is essentially an instantaneous rather than a steady, dependable force.



Current Electricity
When a neutral atom loses an electron it becomes a positive ion. A neutral atom that gains an electron becomes a negative ion. Between any two charged particles a force field exists in which like charges are repelled, and unlike charges are attracted. This force field is called an "electrostatic field." In response to the force being exerted by the field, charged particles move. This movement constitutes an electrical current. In a solid conductor the only mobile particles are free electrons that have escaped from the outer shell of an atom leaving it as a positive ion. In liquids and gases the positive ions are also free to move, an effect we shall encounter in connection with certain types of lighting equipment.

When an excess of electrons causing a negative charge is built up at one end of a conductor, and a deficiency of electrons causing a positive charge is built up at the other end, the pressure caused by the field existing between the two ends will cause the loose electrons in the conductor to flow from the area of excess to the area of deficiency, if permitted .to do so. As the electron differential between the area of excess and deficiency increases or decreases, the pressure differential between them varies as well.

The difference in electrical pressure between two points is measured in units called volts. The volt is named after an 18th-century Italian experimenter named Alessandro Volta, the inventor of the battery. One volt is defined as the pressure necessary to force one ampere of electrical current through a resistance of one ohm. This definition is not too helpful until we understand what is meant by ampere and ohm.

The ampere is named after Andre Marie Ampere, also a late 18th-century electrical experimenter. His experiments dealt in part with the flow of current in a conductor. In consequence the ampere, the unit used to measure current flow, is named in his honor. Since an electrical current consists of a flow of electrons through a conductor, then the measurement of that flow is a count of the electrons passing a designated metering point in a specific length of time. As a comparison, amperage measures the flow of electricity per second the same way gallons per minute measures the flow of water. An electrical flow of 6,250,000,000,000,000,000 electrons per second equals one ampere for that is what a pressure of one volt will push through a resistance of one ohm.

For an electrical pressure (voltage) to push a current (amperage) through any substance, that voltage must be sufficient to overcome the resistance of the substance. All substances, to greater or lesser degrees, are resistant to the flow of electrical current. Conductors such as metals have low resistance. Various insulators such as plastics, paper, glass, or rubber have high resistance, but no material exists that has no resistance. Since the resistances of different materials vary so widely, it is necessary to have a means for measuring these differences. International agreement was reached long ago to standardize on a unit termed the ohm as the measure of resistance. The ohm is named after another late 18th- and early 19-century investigator of electrical phenomena, Georg Simon Ohm. It was Ohm who recognized resistance as an inherent property of all materials. He also worked out the law bearing his name that explains the relationship between voltage, amperage, and resistance.

Ohm's Law

Ohm's Law states an absolutely fixed relationship exists between current, voltage, and resistance such that the current flowing in a circuit is directly proportional to the applied voltage, and inversely proportional to the resistance. Expressed in words, this sounds rather complicated, but it can be reduced to a very simple and easily understood mathematical formula. This formula can be stated three ways, but first for mathematical purposes the following symbols are used:

Electrical current in amperes = I
Electrical pressure in volts = E
Electrical resistance in ohms (D) = R

1. The current in amperes is equal to the pressure in volts divided by the resistance in ohms.
I = E / R
2. The resistance in ohms is equal to the pressure in volts divided by the current in amperes.
R = E / I
3. The pressure in volts is equal to the current in amperes multiplied by the resistance in ohms.
E = I x R
With any two factors known, the third can easily be calculated by either division of multiplication. All that is necessary is to keep track of when to multiply and when to divide. The following diagram is often helpful:



EXAMPLE Using Ohm's Law a device with a resistance of 18 ohms will be connected to a 120V circuit. What amperage will it draw?
I = E / R = 120 / 18 = 6.6667 A
EXAMPLE A countertop appliance draws 4A at 120V. What is its internal resistance?
R = E / I = 120 / 4 = 30
EXAMPLE An electric dryer has a resistance of 10.67 and draws 22.5 A. What voltage should be supplied?
E = I x R = 10.67 x 22.5 = 240
An ohmmeter can be used to read resistances directly only when the circuit is off. However, many electrical devices that show very little resistance when off and cold, increase in resistance dramatically when turned on and hot. A broiler, a toaster, or a tungsten light bulb are examples of this. A 60 watt tungsten light bulb has a cold resistance of only 5 ohms. A resistance of 5 0, with a pressure of 120V would mean that
I = 120 / 5 = 24 amperes
a current of 24 amperes would be drawn by that bulb. What happens in fact is completely different. The filament heats instantaneously which increases its resistance instantaneously from 5 0, to 240 0,. This resistance, however, can be found only by computation rather than direct measurement. This particular computation requires the use of another formula in addition to Ohm's Law. This one was formulated by James Watt and is known as Watt's Law.

Watt’s Law
This law is named after the same James Watt who invented the reciprocating steam engine. After doing so he found it difficult to sell to a skeptical public until he could work out a way to compare its power to perform work with that of a horse. The horsepower ratings for not only steam engines, but also gasoline, diesel, and electric motors are derived from his basic formulations.

In the same way that a fixed relationship exists in Ohm's law between voltage, amperage, and resistance, so in Watt's Law a fixed relationship exists between power, expressed in watts, and amperage, and voltage. Watt's Law states that the power available in watts is equal to the amperage multiplied by the voltage.
P = I x E
There are two other common versions of this formula. One is the current in amperes is equal to the power in watts divided by the voltage.
I = P / E
The other version is the voltage is equal to the power in watts divided by the amperage.
E = P / I
As with Ohm's Law when any two quantities are known the third is obtained by simple multiplication or division. A similar diagram may be drawn for Watt's Law.

Watt's Law provides a simple method for converting watts to equivalent amperage, and vice versa (Figure 1-6). This type of computation is needed, as will be seen in Chapter 8, to determine connected loads on circuits Loads must be known accurately in order to insure that proper wire and breaker sizes are specified. Load computations are also used in troubleshooting to determine when a circuit is overloaded, and help determine proper action when an overload is found.

EXAMPLE A 1 horsepower electric motor draws 746 watts of power at 120V. Will it operate satisfactorily on a 15 A circuit?
I = P / E = 746 / 120 = 6.22 A
No problem!
EXAMPLE A coffee maker drawing 1000 W, a toaster at 1200 W, and an egg cooker at 600 Ware plugged into a 20A 120V counter-top appliance circuit. Any two will operate satisfactorily, but as soon as the third one (no matter which one it is) is turned on the breaker trips. What is the matter?
P = I x E = 20 x 120 = 2400 watts is the maximum the circuit can handle. Above that wattage the breaker should trip.
Coffee maker1000
Toaster1200
Total2200 No problem
Coffee maker1000
Egg maker600
Total1600 No problem
Toaster1200
Egg maker600
Total1800 No problem
Coffee maker1000
Toaster1200
Egg maker600
Total2800 Overloaded by 400 watts


Electrical Measurements
The electrician wiring residences or other small buildings actually takes very few electrical measurements. However, when he does need a measurement, he must know what instrument to use and how to use it. His workhorse and most commonly used instrument is the multimeter (Figure 1-7). This instrument will give readings in AC volts, DC volts, ohms (resistance), or milliamperes. In price they vary from about $20.00 to approximately $1,000.00.

The immense precision of the expensive instruments is not necessary for building wiring. A small, inexpensive instrument is entirely satisfactory. In fact it is preferable since it is compact and can be carried in a pocket while its owner squirms in and out of unlikely nooks and corners in the normal course of completing his work. If it is accidentally smashed in the process, he hasn't lost much.

The multimeter will have a central function selector switch to shift between the various AC (alternating current), DC (direct current), ohms, and milliampere scales. In normal building wiring only AC voltage and ohms scales are used. AC voltages in a building will be either 120 nominal, or 240 nominal. Nominal means that the actual voltage at'any given time might vary anywhere between 1l0V and 120V, or between 220V and 240V. When reading building voltages be sure the selector switch is in fact set on to AC. If, by accident, it is set to DC, there could be 240V AC in a receptacle, but the multimeter will give a reading of 0 volts because there is no DC voltage at that point. Your instrument will gladly give you



accurate information, but you must ask it the right questions. If it is asked whether there is DC voltage in AC outlet, it will correctly answer "0." If asked whether there is AC voltage in a car battery it will equally correctly answer "0."

The ohms scales will primarily be used to check circuit continuity, and to test for shorts. When using the ohms scales be sure the power is off Resistances cannot be read on a live circuit, only on a dead one. If power is on, it will burn out the meter. After setting the selector to ohms, and before taking any readings, short the test probes to each other, and use the "ohms adjust" control to set the meter accurately on O. If this is not done, misleading readings might result.

The measurement of amperage is not commonly necessary when wiring small buildings. However, when troubleshooting it is a very helpful measurement to have when tracking an overload that keeps tripping a breaker. The instrument to use for this purpose is a clamp-on field sensing ammeter (Figure 1-8). This meter when clamped around the power lead from a breaker will detect the electrical field around it and translate the intensity of that field into a measurement of the amperage flowing in that wire. In order to read amperage, this meter must be clipped around the hot wire only. For reasons mentioned in the next chapter, if it is clipped around the complete cable feeding an appliance, it will read 0 instead of the amperage being drawn by the appliance. To read the exact amperage drawn by a plug-in appliance, an adapter such as is shown in





Figure 1-9 is necessary to separate the hot wire from the common in the appliance feed.

In addition to voltage, resistance, and amperage, wattage, the fourth factor in electrical computations, can also be directly measured with a wattmeter. The wiring of buildings discussed here does not require this measurement since wire sizing, breaker sizing, and circuit loading are specified and limited in the code by amperage rather than wattage. In all likelihood the only contact the average electrician will have with wattage measurement will be the installation of the meter box in the service entrance (Chapter 9). It is here that the utility company mounts their watthour meter (Figure 1-10) to record electrical power usage for billing purposes.

Basic Electrical Circuits
Since an electrical current will flow readily through a conductor, it is a simple matter to direct electrical energy from a remote source to a desired point by connecting conductors to form a low resistance path from one point to the other. Conductors so connected become an electrical circuit. The simplest electrical circuit consists of a minimum of four parts (Figure 1-11). They are a source of electrical pressure or voltage. conduc-



tors to connect the source to the use point; an electrical load or using device; and a switch or other mechanism to control that load. Since a current will only flow when the path is complete from the high pressure, or hot side, of the source back to the low pressure, or grounded side, a return conductor is necessary to complete the circuit.

Electrical loads can be connected to a power source in either of two ways (Figure 1-12). They can be connected in series or in parallel. In the case of a series circuit, there is only one path through which current can flow, and consequently the same amperage flows through all parts of the circuit. In the case of the parallel connection, there is a separate electrical path through each load with part of the amperage coming from the source passing through each path. The part of the total amperage drawn that passes through each load is proportional to its wattage and inversely proportional to its resistance.

In Figure 1-13 three loads connected in parallel on one circuit are shown. The total wattage being drawn is the sum of the three loads:



300W
100W
75W
475W
Using Watt's Law to determine the total amperage being drawn:
I = P / E = 475 / 120 = 3.958 amperes
The amperage being drawn by the television alone:
I = P / E = 300 / 120 = 2.5 amperes
Its resistance by Ohm's Law:
R = E / I = 120 / 2.5 = 48 ohms
The fan by contrast draws an amperage:
I = P / E = 75 / 120 = .625 amperes
But has a resistance vastly greater:
R = E / I = 120 / .625 = 192 ohms
Let us note something else that is happening in this parallel circuit that will help in understanding overloads. The total resistance on this circuit as shown, again using Ohm's Law, is:
R = E / I = 120 / 3.958 = 30 ohms

Now, we already have a resistance of 48 ohms, and another of 192 ohms. We have not calculated the third one, but we know it will be somewhere between the two figures. How can the total resistance of the circuit be only 30 ohms? This brings us to the fact that in parallel circuitry there are multiple paths through which the current may pass. Regardless of how high the resistance of a particular path is, as soon as that path exists some current can pass through it-some current that could not pass, and was



not passing through other existant paths. Therefore, the more paths there are, regardless how high their resistances may be, the more current the circuit will allow to pass, because with the opening of each additional path the total resistance of the circuit has been reduced.

In building wiring all power-using devices are wired in parallel because wired this way each is independent of the others. Referring to the series circuit in Figure 1-12, if Load #2 were to break down, # 1 and #3 will stop as well because only one electrical path exists and it has been broken. If #2 in the parallel circuit failed, this would have no effect on either # 1 or #3, because each has independent access to the power source.

In building wiring the basic rule is: "All loads are wired in parallel, all switches are wired in series." A switch completes or breaks an electrical path, but uses no power. It presents either no resistance, or infinite resistance to the passage of an electrical current. Its purpose is merely to open or close the path to some electrical equipment.



Effects of Electrical Energy
Electrical energy can easily be channeled so as to produce heat, magnetism, chemical reactions, and, as some know all too well, physiological effects as well. All of these effects involve the conversion of energy from one form to another. Such conversions always involve some loss.

Mechanical energy applied to an apparatus encounters resistance in the form of friction within the mechanism. In the process of transmitting power from the engine to the wheels of an automobile, some of that power, despite the best lubrication, is lost in friction. Well, actually it is not lost. It is still present in the form of heat that develops at friction points. A transformation of mechanical energy into heat energy has taken place.

Similarly electrical energy is transformed into heat in the process of overcoming the resistance in a conductor. Conductors specifically designed to maximize this transformation are used in the heating elements of certain electrical appliances, such as toasters, broilers, electric ranges, water heaters, clothes dryers, and the other useful electrical heating equipment. These are all common and well known uses of the heating effect that can be produced with electrical energy.

While not commonly thought of in this way the incandescent light bulb is another example of the heating effect of electricity. Inside the bulb an electrical current passes through a filament of tungsten wire. The resistance of the wire causes it to heat white hot, producing light. In the process considerable waste heat is produced, as direct contact with a burning bulb will quickly prove.

The fluorescent light is another example of the heating effect of electricity (Figure 1-14). In this instance filaments do not produce light, but act as heaters and ionizing electrodes. Air is pumped from a fluorescent tube after which a bit of argon gas and a few drops of mercury are introduced. The heater current passed through the filaments vaporizes the mercury. The higher ionizing voltage then ionizes first the argon, then the mercury vapor, producing ultraviolet light. The ultraviolet hits the phosphor coating of the tube, producing visible light. The fluorescent tube is a vastly more efficient light than the incandescent; a far higher



percentage of the electrical energy used appears as visible light and far less is wasted in heat. A touch of an operating fluorescent tube demonstrates the difference.

Other electrical lighting systems such as neon, metal halide, sodium vapor, and mercury vapor lamps are all examples of electrical heating effects.

In addition to producing heat, electricity can be used to produce many other useful results through magnetic effects. As will be discussed in Chapter 2, a magnetic field can produce an electrical current. The reverse is true as well. An electrical current can produce magnetic effects. The electric motor in its many forms is probably the most important use of the electromagnetic effect, but there are many others.

Examples of many other everyday items whose operation is based on magnetism are doorbells, buzzers, telephone transmitters and receivers, solenoid controls, electromagnets, dynamic stereo loudspeakers, and all material recorded on magnetic tape.

Although chemical effects of electricity are perhaps not as commonly encountered as heating or magnetic effects, it is highly likely that this book was printed using electroplated type-a very important chemical effect. You may very well have eaten your last meal with electroplated silverware. An electro-chemical effect produces the power to turn the car engine over every time it is started, and the drycell batteries used in flashlights are all chemical effect items.

The physiological effects of electricity generally are not the ones we are most eager to encounter. However, while we tend to think of these effects as generally unpleasant, there are some extremely useful ones as well. Remember, the pacemaker on which many heart patients depend is an apparatus that regulates the heart beat electrically. The defibrillator found in all coronary care units is another very important lifesaving means of regulating heart action. In addition the medical arsenal contains a number of other pieces of electrical equipment with important uses in the saving and maintaining of life, and the improvement of comfort for ill patients.


*National Electric Code® and NEC® are Registered Trademarks of the National Fire Protection Association, Inc., Quincy, MA

Residential
Wiring
to the 2005 NEC©

It's one thing to install wiring that will carry power from the service entrance to outlets, switches and equipment throughout a home. But that's not enough. The wiring also has to give safe, trouble-free service and pass inspection. That means it has to comply with the latest National Electrical Code.

Here you'll find the basics of residential wiring - your complete guide to installing wiring the right way. You'll learn about:

  • tools and gauges
  • wiring additions
  • switch circuits
  • alterations to old work
  • service entrances
  • troubleshooting
  • rough and finish wiring
  • repairs
The author explains what every electrician needs to know about electricity - how to select the right material, how to follow the plans, the types and spacing of outlets, and permissible loading on general purpose circuits.

This book is for anyone who wants to make a living wiring houses, but who is new or rusty on current rules and theory for electrical work. Emphasis is on what the 2005 NEC allows, and how to avoid the errors new electricians often make. Includes over 20 pages of the 2005 NEC tables that you'll need and use the most.

Jeff Markell has over 30 years of experience in building construction, repair, remodeling and maintenance. He holds a General Contractor's License and a California teaching credential, and has authored several technical manuals.

As an instructor, teaching hands-on electrical wiring to students entering the trade, he needed a practical manual that would bring together all the information apprentice electricians need. Finding none, he wrote this book, explaining both safe wiring and the NEC provisions that govern residential work.