Two-conductor cable should be installed for
conductors are essential for efficient operation of the
two-wire, dc and single-phase, ac circuits.
transmission line. The proper connectors and
Three-conductor cable should be installed for
terminations are also necessary for efficient operation
three-wire, dc, or three-phase, ac circuits.
of the line.
Four-conductor cable should be installed
The inner conductor maybe either solid or stranded.
where two two-wire lighting circuits are run in
the same cable. F o u r - c o n d u c t o r a n d m u l t i -
It may be made of unplated copper, timed copper, or
conductor cable should be installed for con-
silver-plated copper. Special alloys may be used for
trol circuits and communications circuits as
special cables.
necessary.
The dielectric insulating material is usually
To select the proper size cable for a particular
polyethylene or TeflonTM.
installation, you must know the following:
Polyethylene is a gray, translucent material.
The total connected load current
Although it is tough under general usage, it will
The demand factor
flow when subjected to heavy pressure for a
period of time.
The allowable voltage drop
TeflonTM is a white opaque plastic material that
To compute the total connected load current
withstands high temperatures and remains
for dc power circuits, you add the sum of the rated
flexible at relatively low temperatures. It
current of the connected loads as listed on the
has a peculiar quality in that nothing will
identification plates of connected motors and
appliances. Add an additional 100 watts for each
stick to it. Also, it is unaffected by the usual
receptacle not specifically indicated. To
solvents.
compute the total connected load current for
Braided copper is usually used for the outer
ac power circuits, add the connected load
conductor, and it may be tinned, silver plated, or bare.
current of the connected motors and appliances
The outer conductor is chosen to give the best electrical
vectorially.
qualities consistent with maximum flexibility.
The demand factor of a circuit is the ratio of the
The protective insulating jacket is usually a
maximum load averaged for a 15-minute period to the
synthetic plastic material (vinyl resin). Neoprene
total connected load on the cable. If you cannot
determine the feeder demand factor for a group of loads,
rubber is generally used on pulse cable; silicone
you may assume a value of 0.9. For power systems
rubber jackets are used for high-temperature
supplying a single-phase load or for a lighting system
applications.
branch, submain, and main circuits, the demand factor
Armor is needed for protection. It may be braided
is unity.
aluminum, or sometimes galvanized steel, similar to that
The voltage drop (difference in voltage
used on power cables.
between any two points in a circuit) is expressed
as a percentage of the rated switchboard (or
switchgear group) bus voltage or the transformer
SELECTING CABLE
nominal voltage. The maximum percentage of
voltage drop allowed for a circuit is specified
When selecting cable, use all reference data
by the Naval Sea Systems Command and
available. Electrical cables installed aboard Navy
varies according to the intended service of the
vessels must meet certain requirements determined by
circuit.
the Naval Sea Systems Command These requirements,
published in the General Specifications for Ships of the
CABLE INSTALLATION
U.S. Navy ( N A V S E A S 9 A A 0 - A A - S P N - 0 1 0 /
GEN.SPEC), are too numerous to cover in detail in this
TRAMAN; therefore, only the more basic requirements
EMs install cable whenever necessary to repair
damage or to accomplish authorized ship alterations
are included.
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