ted firefighter fatalities by electrocution. The
purpose of this program is to:
give you a basic knowledge of how electricity
works,
help you to understand basic construction,
explain configurations of the electric utilities,
make you aware of the hazards of electricity.
This chapter will help you better understand what
precautions need to be taken when working
around electrical equipment.
Electricity is invisible. When you look at an electric
wire that could be energized from 120 volts all the
way up to 500,000 volts, it seems harmless enough.
That is why electrical energy is often referred to as
the silent killer and remains a hazardous form of
energy that has to be dealt with safely.
No matter what the voltage is in an electrical con-
ductor, it is dangerous and can injure and/or kill
emergency workers.
Some people believe that 120 volts (normal house-
hold current) is harmless. However, throughout the
electrical industry there have been people killed when
they have made contact with 120 volts. Any voltage
can kill! It all depends on the situation, the amount of
current involved, the part of the body affected, the du-
ration of contact, and environmental conditions (wet
or dry) at the time of contact.
Electricity is a blessing that is often taken for
granted and must be treated with respect. Electrocu-
tion is the fifth-leading cause of workplace death.
The majority of these fatalities are caused by the fail-
ure to recognize and avoid electrical hazards.
ELECTRICITY
THE BASICS
This section provides a general summary of electric-
ity and electrical equipment. Key safety and tactical
points are indicated.
Suppose nothing is coming out of a hose, but there
is water under pressure inside it. If you open the
valve, the force of that internal pressure releases a
spray of water. An energized wire is similar. The
force that causes electrons to flow is called voltage,
and like water, the greater the pressure pushing elec-
tricity through a line, the higher the voltage. In water
terms the pressure is measured in pounds per square
inch. With electricity, pressure is measured in volts.
Voltage is the electric force that causes the free
electrons to move from one atom to another. Just
as water needs pressure to force it through a hose,
electrical current needs a force to make it flow. A
volt is the measure of electric pressure. Voltage is
usually supplied by a battery or a generator.
Current is electricity in motion. It measures the
amount of electrons that can flow through a ma-
terial like a conductor. Electric current is mea-
sured in amperes, or amps for short. Amperes
is like the amount of water flowing through a
hose in a certain amount of time or the amount of
electricity flowing through a wire.
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CHAPTER #
CHAPTER
I
RECOGNIZING AND
AVOIDING THE HAZARDS
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page 50.qxd 1/20/06 10:52 AM Page 50 ResistanceThe opposition to electrical current
flow, measured in ohms.
ConductorsThese are made of materials that
electricity can flow through easily.
These materials are made up of atoms whose elec-
trons can move away freely.
Some Examples of Conductors Are
Copper
Aluminum
Platinum
Gold
Silver
Water
People and Animals
Trees
Electricity will always take the shortest path to the
ground. Your body is 70 percent water, and that
makes you a good conductor of electricity. If a power
line has fallen on a tree and you touch the tree you be-
come the path or conductor to the ground and could
be electrocuted.
Insulators are the opposite of conductors. The
atoms in these materials are not easily freed and
are stable, preventing or blocking the flow of
electricity.
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51
Some Examples of Good Insulators Are
Glass
Porcelain
Plastic
Rubber
The rubber or plastic on an electrical cord provides
an insulator for the wires. By covering the wires, the
electricity cannot go through the rubber and is forced
to follow the path on the aluminum or copper wires.
As mentioned above, electricity flowing through a
conductor is similar to water flowing through a pipe.
If you take a water pipe with the faucet shut off, there
is water in the pipe putting pressure (volts) on the pipe.
However, there is no flow of water (amps) since the
faucet is turned off. This is the same situation found in
a home when the electrical wiring is connected to a TV
or other appliance and the switch is turned off.
When the faucet is opened, water starts to flow
(amps). The rate at which the water flows depends on
two things:
1. The size of the pipe. (electrical
comparisonresistance)
2. The pressure of the water. (electrical
comparisonvolts)
Once you have pressure (volts) and flow (amps)
you have accomplished work (power, watts). Just like
the water that comes out of a faucet to fill a pot, wa-
ter the lawn, and so on, the electricity is running the
TV, VCR, lighting, and so on. Electric power is the
term used for the product of the voltage and current
in a circuit.
The length of time that you let the water flow will
determine the gallons that are used; this is measured
by the water meter. Likewise, the length of time the
power is used is measured in watts by the electric me-
ter and billed as a kilowatt-hour (1 kw
1,000 watts).
Electricity is always trying to reach earth, which is
ground, through the path of least resistance. In order
to control electricity, insulators are used to isolate the
energized conductors from all sources of ground po-
tential. Air is a natural insulator; once an electrical arc
has started the air becomes ionized which is now con-
taminated. The arc will continue until it is interrupted.
Tactical Point
If you discover someone
who has made an electrical contact, do not attempt
to pull the victim away from the source of con-
tact with your hands. The power supply should
be disconnected by the power company first.
This may be done remotely by phoning the
power company.
If someone is working from an elevated aerial
apparatus and makes contact with an energized
electrical conductor,
do not climb onto the vehi-
cle to lower the injured person by using the
lower controls of the aerial apparatus until the
power source has been de-energized or the aer-
ial apparatus is clear of the electrical conductor.
The risk of electrical shock or contact can be
reduced by:
being able to identify electrical wires and
equipment as you arrive at the incident.
maintaining a safe working distance from any
electrical wires or equipment.
Caution
Consider all downed wires as ENER-
GIZED until the utility representative confirms
they are safe.
ffh1060x_ch01.qxd 1/20/06 9:39 AM Page 51 THE ELECTRIC SYSTEM
Generation
Electricity generating or power plants may be large
or small, and generation is produced by several
means: fossil, hydro, or nuclear. Generation is pro-
duced by several means: fossil, hydro, or nuclear. Ap-
pearances of the power plants differ, as does the
equipment in the plant. However, there are certain
conditions and equipment that are somewhat com-
mon to all power plants, such as the turbine, boiler,
condenser, and electrical switch rooms.
The voltage that is produced by the generators is
stepped or raised up through the use of power trans-
formers to levels used to transmit the power by elec-
trical transmission lines to locations miles from the
generating stations. These transmission line voltages
range from 115,000 to 500,000 volts. Transmission
line towers are usually 100 to 200 feet high and run
in a straight line along utility right of ways. In most
cases, the wires with the highest voltage are those at
the tops of utility poles. Keep in mind that most
poles also have other utility wires, such as telephone
and cable.
The electrical power is carried great distances on
these towers to large substations. An electric substa-
tion performs one or more of the following functions:
(1) It transforms electric energy from one voltage to
another, (2) it serves as a control center and switch-
ing facility, or (3) it serves as a center for distributing
electric energy to end-use customers.
Substations can be classified into three categories:
inside, outside, and a combination of both. Some are
hidden from site by constructing a three-sided house
around the station.
All substations contain electrical equipment, with
some being insulating mineral oil filled, and/or pressur-
ized insulating gas, such as sulfur hexafluoride (SF-6).
At these substations the voltage is stepped down,
again by the use of power transformers, to 34,500
volts. The 34,500-volt electrical conductors are car-
ried to smaller substations on high utility poles rang-
ing from 60 to 90 feet in height that run along power
right of ways.
At these smaller substations, the voltage is once
again reduced, this time to the primary voltage level
(2,400 to 19,900) volts. These conductors are carried
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on smaller utility poles (40 to 50 feet in height)