MODULE E-1 ELECTRON THEORY
It has been estimated that if two
grams (0.070 ounce) of electrons could be collected into two
equal spheres and these spheres were a distance of 0.39"
apart, they would repel each other with a force of 320,000,000,000,000,000,000,000
tons. A force greater than the weight of the water in all the
oceans of the world.
Insulators are elements that have six or more valence electrons.
These electrons are very difficult to free and tend to catch
any free electrons. An atom is completely stable when
its outer valence is filled with 8 electrons and will resist
any activity. The atom with 7 valence electrons is the most active,
always looking to catch a free electron and is the best insulator.
There is no such thing as a perfect insulator. Considered to
be the best insulators are glass, mica, plastics, rubber, dry
air, ceramics, and slate.
It has been estimated that a single electron moves rather slowly
at a rate of approximately 3 inches per hour at one ampere of
current flow. But the impulse of electricity is extremely fast.
It is assumed that the speed of the electrical impulse is 186,000
miles per second, which is the speed of light. When one electron
enters a conductor with billions of electrons, the impulse must
be fast to knock one out the other end of the conductor and move
billions to do so.
If you should attempt to count the electrons in one ampere of
current for one second, you would have to count 1000 electrons
per second for 190 million years without stopping.
Water and electricity flow under very similar conditions. That
is to say, each of them must have a channel, or conductor, and
each of them requires pressure to force it onwards. Water however,
being a tangible substance, requires a hollow conductor; while
electricity, being intangible, will flow through a solid conductor.
The metal of the water pipe and the insulation of the electric
wire serve the same purpose; namely that of serving to prevent
escape by reason of the pressure exerted.
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Module E-2 OHM'S LAW
Ohm's Law is one of the most important
things that you will use throughout your electrical career. It
is a mathematical tool which is of the greatest use in determining
an unknown factor of voltage, current, or resistance in an electrical
circuit in which the other two factors are known.
Directly proportional means that one factor will be increase
in proportion to a decrease in another factor.
Example: The current increases
to two amps as the voltage increases to 2 volts, The resistance
remained the same; one ohm.
Inversely proportional means
that one factor will be increased in proportion to a decrease
in another factor or vice versa.
Example: The current will increase
in proportion to a decrease in resistance. The current doubled
to 20 amps with a decrease in resistance to 0.5 ohms.
Doubling the cross-sectional
area of a conductor will reduce the resistance of the conductor
by one-half.
Put your finger on the one
you want to solve and the other two knowns will show you how
to solve it.
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Module E-3 MAGNETISM AND ENERGY
The story is told that in the
year 500 B.C., a shepherd boy who lived in a Greek town named
Magnesia, often used a walking stick with an iron tip to help
him climb the stony hills. One day the tip of his walking stick
actually stuck to a stone. He reached down and felt the stone.
It didn't feel sticky, and nothing else was attracted to it.
Only the iron tip of his stick clung to the rock. This rock is
called a loadstone.
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The picture to the
left shows the relationship of induction to water. When a garden
hose is wrapped around a post several times, the coiling will
oppose the normal flow of water to slow it down. A plumber refers
to this as back pressure, like a restriction to the flow. Electrically
it offers a resistance to the normal flow of current. We call
it inductance. |
The carbon brush, as it slides on
the revolving commutator, reverses the connections of the connection
in the armature to the external circuit at the instant when the
voltage of the conductors is zero and changing in direction.
The commutator switches the wires outside the generator while
the armature turns, thus keeping the current flow in the same
direction at all times. If a commutator is not used, the current
coming out of the generator will change direction as the armature
turns.
As the conductor cuts through the magnetic lines producing the
torque to rotate the motor, it acts like the force that the wing
of an airplane feels as it lifts. The top of the wing feels a
lower pressure than the bottom. This lower pressure is what causes
the wing to create lift, enabling the plane to become airborne.
I like to think of the secondary winding as a baseball catcher's
mitt. As the alternating current reverses direction through the
primary winding, an electron is induced into the invisible magnetic
field and the catcher's mitt (secondary winding) catches these
electrons.
The tendency of matter to resist change is called inertia
(in nur sha). The word inert means sluggish to change and
lackadaisical. The animating force that prevents inertia from
taking over is called energy.
The Law of Conservation of Energy states that energy is neither
created nor destroyed. The total amount of energy in the universe
always remains the same.
The pages of an old book turn yellow after years of time. The
pages of the book are slowly releasing chemical energy as they
combine with the oxygen of the air surrounding the book. The
pages actually become hotter than the surrounding air and the
yellowing of the pages is a result of this slow burning from
chemical energy.
100w
If you have trouble relating
to six trillion watts, a human being operates on 100 watts. The
brain 20 watts and the body 80 watts. You are equivalent to a
100 watt light bulb.
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Module E-4 SAFETY & TOOLS
Anyone working in construction is
exposed to potentially dangerous conditions and situations. However,
it is possible to complete hundreds of jobs without any injury
whatsoever. This goal of safety only requires that anyone working
in construction to be aware of the main sources of danger. Not
knowing the possible sources of danger, or worse, being inattentive
to those sources are the main reasons there are injuries in construction
work. You must take the proper precautions and practice the basic
rules of safety - one must be safety conscious at all times,
and this safety consciousness must become second nature to you.
OSHA'S new standard is a set of regulations aimed at protecting
the construction industry's five million workers. Falls
are the leading cause of worker fatalities, accounting for
more than 218 job related deaths per year. I once read a safety
poster which read: "You can walk with an artificial leg,
you can chew with false teeth, but you can't see with a glass
eye."
Most people think that high-voltage is the main cause of fatal
electrocutions. Actually, it's the amount of current passing
through the body that determines the effect of a shock; currents
over 15 mA are dangerous, over 75 mA could be fatal. Of course
the higher the voltage, the more chance there is of pushing more
current through the body.
The U.S. Consumer Product Safety Commission estimates that 110,000
people receive emergency hospital treatment each year for serious
injuries due to misusing simple hand tools.
Your mind and your hands work together as the message flows from
your brain to your hands to your tools. Once you become trained
and have practice, it will be a natural reflex. It will be like
riding a bicycle; once you learn it and apply it, you'll never
forget it.
Connections can be over-torqued as well as under-torqued. The
inch-pounds of torque required by the manufacturer is the ideal
value that must be achieved as closely as possible to get the
most effective electrical connection, minimizing creep and cold
flow of the conductor metal and prevent overheating due to increased
contact resistance.
When joining two pieces of wood of different thicknesses, drive
nails through the thin piece into the thick one. Use nails three
times as long as the thickness of the inner piece so that two-thirds
of their lengths will be anchored. For more security, drive nails
at angles, slanting away from one another. For maximum holding,
drive a longer nail through both pieces and hammer the protruding
point over.
1000v Not all tools
with plastic coatings or handles provide protection against electrical
shock. Many tools have plastic handles that are designed solely
for extra comfort. Use only tools that are marked with the official
international 1,000 volt rating symbol.
The regular conduit hand bender gives more of a sweep in the
bend. The one-sweep design permits pinpoint precision even by
the inexperienced users. Both of these hand benders will bend
EMT, IMC, and rigid metal conduit. Bending larger conduits over
1" is done with a hydraulic powered bender.
When carrying a long, heavy ladder, i'ts always a good idea to
mark the center (balance point) with tape or paint. When you
pick up the ladder, reach for the marked area and you'll be surprised
how much easier the ladder is to handle.
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Module E-5 WIRING
METHODS RESIDENTIAL
The term loadcenter is used to describe
a light-duty type of panelboard used for residential and smaller
commercial and industrial applications.
A conductor can be round, solid, stranded, rectangular, copper,
aluminum, etc. An example of a rectangular conductor would be
the busbar in a panelboard that the breakers connect to. The
plans are the roadmap of the work to be done. Persons unfamiliar
with the symbols and specifications find the plans difficult
to follow. An experienced electrician will actually make his
own plans for certain jobs.
In some cases, instead of having a ceiling fixture, split-wired
duplex receptacles are used. By removing the tab on the hot side
(brass colored) of the duplex you split it into two circuits.
One half of the duplex will remain hot from the black wire and
the other half will be energized from the red wire which is connected
through the single-pole switch. This requires a 3-conductor cable
between the receptacles. This will be further explained in detail
later in this module.
The location of the service to a building is extremely important
as this is where the big money is spent.
The service can be overhead or underground. The key in a residence
is to locate the service and panelboard close to the heaviest
loads. The heaviest loads would be the highest wattage appliances
such as the range, water heater, clothes dryer, air conditioner,
electric heat, etc.
These appliances require the larger size cable which is the money
factor. Always try to keep these circuits at a minimum distance
from the panelboard.
A garage that is close to the kitchen is an excellent location
for the panelboard.
When you place devices in a box, the stiffness of the wire can
sometimes cause one or more connections to loosen slighty. Loose
connections have resulted in overheating, arcing, and fires.
Always fold the wires carefully so when installing the device
you will not put any pressure against the connections. Don't
use a box too small.
To make it real simple, you can't have a neutral in a 2-wire
(120 volt) circuit. You must have a 3-wire circuit and read a
voltage potential between the hot wires.
A despard-type device is small in size, as up to threedevices
may be mounted in a standard device box. They are easily mounted
in the same strap, and then the strap is mounted to the device
box.
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Module E-6 WIRING METHODS COMMERCIAL
The wiring methods used for commercial
and industrial buildings generally require the wires to be installed
in some form of raceway. The Code defines a raceway as: An enclosed
channel designed expressly for holding wires, cables, or busbars.
An auxiliary gutter serves the same function as a long junction
box would. Sometimes it is necessary to run large conductors
for a short distance but to make several taps to the conductors,
in the case of multiple services.
There are five types of conduit that must be properly bent, in
the field, by the installer to form the complete conduit system
with each type having its own unique features. Electrical metallic
tubing (E.M.T. or thinwall), rigid steel conduit (rigid), intermediate
metal conduit (IMC), rigid aluminum conduit, and polyvinylcholoride
(PVC) conduit. Each type of conduit has a different wall thickness,
but the internal diameter is approximately the same.
I have even used a nylon string in tight places to cut the PVC.
By see-sawing the string back and forth, the friction created
actually cuts the plastic conduit.
The effective grounding path is like a chain. It is as strong
as its weakest link. The mechanical connections of conduits and
boxes are a vital factor in the strength of the grounding path.
Sometimes a box is added in a wall where there is no stud to
mount the box to. Drywall is not strong enough to support screws
so a special pair of metal straps are used to secure the box
in the wallboard. Insert one strap on each side of the wall opening
for the box, and push the box into the opening. Then bend the
short ends of each strap down into the inside of the box. Be
sure they are bent back sharply over the edge of the box, and
lie tightly against the inside walls of the box, so they cannot
touch the terminals of the device being installed. These straps
are called, by the electrician, "madison straps" or
"hold-its".
A basic color code, numbering system, and case color system is
used to identify the load level or strength. The powder charges
are numbered 1 through 6 with 1 being the weakest. The powder
charges are also color coded using 1-grey, 2-brown, 3-green,
4-yellow, 5-red, 6-purple. The case colors are brass and nickel.
A hickey-type hand bender generally is used for rigid conduit
sizes 1" and smaller. A 90° bend is made by making several
gradual segment bends (approximately 10° at each position)
sliding the bender along the conduit and bending in small amounts.
For larger sizes of rigid conduit a hydraulic bender is used.
This is a popular bender for kicking the stub-up back into the
wall.
Offsets and saddles are easier to bend with the handle of the
bender placed on the floor with the bender up at waist level.
Bend the conduit by putting pressure on the conduit close to
the bending shoe. Bending the conduit with pressure close to
the bending shoe, forces the conduit between the supporting walls
of the shoe, which keeps the conduit from kinking, and in this
position, it's easy to see the degree marks on the bender and
accurate bends can be made.
On large conduit jobs where there are many long runs, electric
blower/vacuum equipment is used which will quickly either blow
or pull a fish line through the conduit. The fish line is then
used to pull a pulling rope through the conduit and the wires
are connected to the rope.
An electrical connection that is overtightened can cause several
problems. Overtightening can flatten the conductor to a point
that it breaks. Overtightening the connection can also cause
the connection to heat up. The conductor will push away from
the stud area causing the conductor to cup which reduces the
amount of contact with the lug. This smaller contact area causes
overheating just as a loose connection will. Overtightening can
damage the lug by causing small hairline cracks in the lug.
Signs of trouble in aluminum wire systems include warm-to-the-touch
face plates on the receptacles or switches, flickering lights,
circuits that don't work, or the smell of burning plastic at
the receptacles or switches. Unfortunately, not all aluminum
wired connections provide such easily detected warning signs;
aluminum wired connections have been reported to fail without
any prior indications or problems.
Ground fault receptacles are used often when only the one outlet
is to be protected, such as in a bathroom at the sink or a kitchen
counter receptacle. This type of receptacle can provide ground
fault protection for only its outlets or it can be wired so that
other outlets down stream can be protected by the same receptacle.
A test button is provided to trip the receptacle intentionally
to insure the proper operation with a reset button to restore
the power to the receptacle.
Fluorescent lamps were first introduced in 1938 and operate totally
different from incandescent lamps. When a substance is exposed
to rays such as X-rays or ultraviolet rays and emits light as
a result of this exposure, the substance is said to be fluorescing.
Fluorescent lamps use less energy than incandescent lamps. Fluorescent
lamps convert approximately 23% of its input energy to light,
and incandescent lamps only convert 11% to light.
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Module E-7 THE SERVICE
As an electrician it is very important
that you understand the definition of branch circuit, feeder,
service, etc. as the design rules change on each part of the
system. A panelboard provides overcurrent protection for the
circuits contained within.
A panelboard generally contains a means for switching the circuit
on or off. Some of the older panelboards have a snap switch and
a fuse. Most panelboards today contain circuit breakers which
provides both overcurrent protection and a means for switching
the circuit.
System grounding means that the service neutral conductor, grounding
electrode conductor, service entrance equipment, and all metallic
pipes, must be bonded together at the service. The equipment
grounding conductor, or raceway, is bonded to the neutral and
grounding electrode conductor at the neutral block in the service
equipment panel only.
The number one violation of grounding is the bonding of the grounded
neutral at sub-panels and other locations throughout the electrical
system.
The difference between an installer and an electrician is education.
An electrician is taught that a circuit must also not work at
certain times. This is called protection (safety). This is as
important as the circuit working.
Whereas a ground fault current normally falls within one and
six times the normal current, the short-circuit current is quite
high. The short-circuit or fault current can be many hundreds
of times larger than the normal operating current. A high-level
fault current may be 50,000 amperes or larger. If not cut off
within a matter of a few thousandths of a second, destruction
and damage can become severe; insulation damage, melting of conductors,
arcing, and fires.
Panelboards which are designed to accept tandem breakers are
designed so the mounting cam on the tandem breaker can only be
installed in a position that has a mounting pan rail slot which
will accept the cam. This prevents the panelboard from having
over 42 overcurrent devices.
The lug may be rated for 90°C but this does not give permission
to the installer to use a 90°C conductor at 90°C ampacity.
Every electrical component in the entire circuit must be 90°C
rated.
When applying the variables to circuit designing often it is
required to use a larger conductor for voltage drop, ampacity
corrections, etc. The question that comes up is how can you properly
install a #4 conductor to a 20 amp circuit breaker? The terminal
lug isn't big enough. UL listed splicer/reducer lugs are available
for this purpose.
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Module E-8 GROUNDING
Sometimes too much emphasis is put
on one's knowledge of Code rules and sizing of bonding jumpers,
electrode conductors, etc. Before one can discuss proper sizing
of grounding conductors you must first understand the reasons
for grounding a system, theory, Ohm's law, and what takes place
when a fault condition occurs in the system.
When a conductor or metal object is connected to an earth electrode,
it is forced to take the same zero potential as the earth. Any
attempt to raise or lower the voltage of the grounded object
results in current passing over the connection until the potential
of the object and the potential of earth are equal.
Under normal conditions, the current flow would be the same in
both wires. But with a ground-fault leak to metal conduit, the
current in one wire does not equal the current flowing in the
other wire. When this happens, the induction in the secondary
winding of the transformer will cause the sensing unit to operate
the GFCI.
Today, plugs and receptacles are polarized, which means the pins
on the plugs and receptacles are opposite in size so they can
only be plugged one way into a receptacle.
Grounding is not only to keep enclosures and equipment
at earth potential, but also to provide a path of low-impedance
back to the source to allow enough current to flow to operate
the overcurrent device (fuse or circuit breaker) when a fault
occurs.
If an overcurrent protective device opens a short-circuit current
in less than one-half cycle, (before it reaches its total available
value), the device is a "current limiting" device.
If not limited, short-circuit currents can reach levels of 30,000
to 40,000 amperes or higher in the first half cycle of a 60 cycle
AC circuit. The heat produced in the circuit by the immense energy
of short-circuit currents can cause severe insulation damage
or even an explosion.
The terms earth and ground are often misused in our electrical
industry today. The words seem almost alike, but are not. An
airplane 35,000 feet up in the sky has a ground bus and grounding
conductors, etc. but the airplane is not connected to earth.
To use earth and ground as the same meaning is obviously in error.
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Module E-9 MOTORS-BOX
& CONDUIT FILL
After the hermetic motor-compressor
sits idle for a period of time, the refrigerant reaches a temperature
of that of the ambient and provides poor cooling for a short
period of time on start up. Consequently, the motor heats up
faster than an ordinary motor. This is the reason for the different
rules of Articles 430 and 440.
Circuit breakers suitable for heating, air conditioning, and
refrigeration equipment comprised of multimotor or combination
loads are labeled HACR type.
HACR type circuit breakers are the same as other type inverse-time
circuit breakers, except they have been additionally investigated
by UL and determined to be suitable for motor branch circuit
protection on group installations. The additional investigation
includes tests to determine if the circuit breaker affords an
appropriate level of protection for the circuit components. UL
testing is performed on circuit breakers and equipment intended
for use with HACR circuit breakers.
A motor is designed to allow for a temporary overload when the
motor is required to deliver more than its rated horsepower only
for a short period of time. If this overload would continue,
then the overload which senses this increase of current (heat)
will open, thus protecting not only the motor but also the wiring.
Shown below is a main wiring diagram of a three-phase magnetic
motor starter with 3 thermal overloads. The starter is controlled
by a start-stop push button control circuit using the holding
circuit. The 3 overload interlocks 
are connected in series with the coil. The 3 thermal overloads
are connected in series
with the motor. The control wires are shown in a fine line, the
power wires in a heavier line.
We now need to learn how to calculate the maximum number
of wires the Code allows in a box or conduit
Note:
Each strap holding a device (switch or receptacle) counts as
two conductors, if the strap holds a duplex or triplex receptacle,
it still counts as two conductors.
The number
and size of conductors in any raceway shall not be more than
will permit dissipation of the heat and ready installation and
withdrawal of the conductors without damage to the conductors
or to their insulation. Even though a GFCI receptacle is larger
than a standard duplex receptacle and a dimmer switch is larger
than a standard single pole switch, the Code still counts them
as the same size device in calculating box fill.
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Module E-10 INSPECTION-MAINTENANCE-TROUBLESHOOTING
After the equipment has been installed
and connected, it is the electricians job to test the wiring
to see if it has been installed properly. Tests will verify that
the wiring, receptacles, switches, and light fixtures are all
operating correctly. These tests are very important, as they
will reveal any defects in the wiring or equipment.
Troubleshooting involves both visual inspection and electrical
testing. Troubleshooting is locating the problem once it occurs.
Should the tests you run on a circuit indicate that it is not
operating correctly, then you will perform various troubleshooting
procedures that will help you locate the problem.
Signs of violent corona when a substation is energized should
be reported. Corona is an electrical discharge phenomenon occuring
in gaseous substances such as air. High electrical pressure exceeding
the breakdown level of air lead to corona discharges. Mild corona
will have a low sizzling sound. As it increases, the sizzling
sound becomes louder and will have sounds of popping and crackling
as flashover level nears. Corona ionizes the air, converting
the oxygen to ozone, which has a distinctive odor. Mild corona
may be normal and be more noticeable when humidity is high.
Proper bolt tightness torque values for all types of joints involved
should be available in manufacturer's maintenance and instructional
literature. The Code requires in section 110-3b that all electrical
equipment is to be installed as listed, and this requires torquing
the connections.
Installing more than the Code maximum permitted conductors in
a box has caused accidents and fires. Forcing the receptacles
into a crowded box tends to loosen the connections thus resulting
in a high resistance fault (heat).
As pinholes or cracks develop, moisture and foreign matter penetrate
the surfaces of the insulation, providing a low resistance path
for leakage current. Now the insulation which was good has become
a partial conductor.
Schematic diagrams are arranged for simplicity and ease of understanding
circuits without regard for the actual physical location of any
components. The schematic is always drawn with contacts shown
in a de-energized position.
Dim or flickering lights, arcs or sparks, sizzling or buzzing
sounds from the electrical system, odors, hot switch plates,
loose plugs and damaged insulation, among other things, are signs
of potential hazards.
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