CHAPTER 12
SHIPBOARD ELECTRICAL EQUIPMENT
Aboard modern naval ships, most auxiliary
machinery and equipment is run by electricity.
Regardless of rate or rating, all personnel assigned
to a ship will operate some electric devices in the
performance of their duties. Electrical equipment
is dangerous if handled incorrectly; therefore,
you must observe all applicable safety pre-
cautions when working with or around electrical
equipment.
In this chapter, we will discuss basic concepts
of electricity, electrical terms, electrical equip-
ment, and applicable safety precautions. You will
find additional information on the basic principles
of electricity in the Navy Electricity and
Electronics Training Series (NEETS), modules 1
and 2, NAVEDTRA 172-01-00-79 and NAVED-
TRA 172-02-00-79.
INTRODUCTION TO ELECTRICITY
Some materials will conduct electricity, and
some offer more resistance than others. Metals
such as silver, copper, aluminum, and iron offer
little resistance and are called conductors. In
contrast to conductors, some materials such as
wood, paper, porcelain, rubber, mica, and plastics
offer high resistance to an electric current and are
known as insulators. Electric circuits throughout
the ship are made of copper wires covered
with rubber or some other insulator. The wire
conductors offer little resistance to the current,
while the insulation keeps the current from passing
to the steel structure of the ship.
Definite units have been established so we can
measure the electrical properties of conductors.
Also, there are terms used to describe the
characteristics of electric currents. A brief review
of these fundamentals is given in the following
sections.
ELECTRIC CURRENT
The flow of current through a wire can be
compared to the flow of water through a pipe.
Current is the rate at which electricity flows
through a conductor or circuit. The practical unit,
called the ampere, specifies the rate at which the
electric current is flowing. Ampere is a measure
of the intensity or the number of electrons passing
a point in a circuit each second.
ELECTROMOTIVE FORCE
Before water will flow through a pipe, there
must be water pressure; before an electric current
can flow through a circuit, there must be a source
of electric pressure. The electric pressure is known
as electromotive force (emf) or voltage (E). The
source of this force may be a generator or a
battery.
If you increase the pressure on the electrons
in a conductor, a greater current will flow, just
as an increased pressure on water in a pipe will
increase the flow.
RESISTANCE
Electrical resistance (R) is that property of an
electric circuit that opposes the flow of current.
The unit of resistance is known as the ohm (S2).
WATT
Power (P) is the rate of doing work. In a dc
circuit, power is equal to the product of the
current times the voltage, or P = I x E. The
practical unit of power is the watt (W) or kilowatt
(kW) (1,000 watts). Power in an ac circuit is
computed in a slightly different way. If you are
interested in how ac power is computed, see
chapter 4 of Introduction to Alternating Current
and Transformers, NAVEDTRA 172-02-00-85.
GENERATOR TYPES AND DRIVES
A large amount of electricity is required
aboard ship to power machinery that supplies air,
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