INTERIOR COMMUNICATION SYSTEM
A. PRECAUTIONS, MAINTENANCE OF CIRCUITS, INSPECTIONS,|
TROUBLE SHOOTING, AND REPAIRS
19A1. Precautions. A live wire always carries
potential danger if it is not handled properly.
Accidents can be prevented if the following
precautions are observed:
1. A circuit should be disconnected before
starting work on it.
2. A test lamp or other suitable device,
depending on the maximum voltage that may be
encountered, should be used to determine
whether or not a circuit is alive.
3. A tool with a metal handle should never
be used unless the handle is insulated with tape.
4. Only one hand should be used when
working on a circuit that is alive.
5. Electrical machinery should not be
started after an overhaul until an inspection has
been made for loose bolts, improper clearance,
tools adrift, and so forth. The speed of the machine
after starting and also the ammeter readings of
field and armature current, should be
checked with the instruction books.
6. Any conditions causing sparking should
be examined and rectified at once.
7. Inflammable liquids must not be used
about electrical machinery as a spark might
8. Emery cloth must never be used on
electrical machinery. Use sandpaper, but sparingly,
and only when absolutely necessary.
9. All protective devices for electrical machinery
panels, circuits, and so forth, such as
fuses, circuit breakers, no voltage and overload
releases, and the like, must be kept in proper
working order and at their designated settings
at all times.
19A2. Maintenance of class A-1 circuits.
Class A-1 circuits are those considered essential
to the safety of the ship and they should therefore
be given particular attention. All A-1 circuits
should be in operation or available for
operation 24 hours a day. Tests and inspections
should be limited to isolated parts of the circuit,
if possible. Parts of all circuits can be isolated
or deenergized for tests or repairs without making
the complete system inoperative.
19A3. Selsyn maintenance. See Section 10B2,
on selsyn maintenance.
19A4. Keeping circuits in operation. All
interior communication and fire control circuits
should be energized and operated in all positions
and from each control at least once each
19A5. Inspecting control units. Operation
of interior communication and fire control units
such as telephones, jack boxes, contact makers,
transmitters, indicators, relays, bells, buzzers,
horns, and sirens should be checked once each
19A6. Inspecting connections. The wiring
and electrical connections of all interior
communication and fire control switchboards should
be inspected once each month.
19A7. Over-all inspection. An over-all check
should be made when operating conditions show
it to be necessary, or at least every 18 months.
The following steps constitute an over-all check:
Deenergize each switchboard; check all bolted
connections for cleanliness and tightness; inspect
individual leads for chafing; clean bus
bars; check securing bolts; remove any dust or
lint; calibrate motors; overhaul trouble indicators;
tighten all contacts, using new lock or
shakeproof washers wherever possible.
19A8. Inspection before getting underway.
Telegraph indicator and communication circuits
that are to be used while getting underway or
standing by should be tested at least an hour
before the time designated for getting underway.
These circuits are, in general, the class
19A9. Trouble shooting. It is not difficult to
maintain circuits in operating condition if
defects are located and remedied as soon as
possible. If this is not done, more serious troubles
are liable to result. For example, a single ground
may have little effect on the operation of a
motor, but if it is not removed, there is danger
that a second ground will occur and produce a
It is necessary to become proficient in testing
a circuit and locating the exact spot at
which any trouble occurs, without an undue
waste of time spent in guessing or in unsystematic searching.
19A10. Grounds, shorts, and open circuits.
Trouble in electrical circuits is due to three
major causes: grounds, short circuits, and open
When trouble occurs in a circuit, it is possible,
in most cases, to tell at once which of these
major causes is responsible. Knowing this, it is
not too difficult to make a search and find the
exact location of the trouble.
19A11. Grounds and their causes. Grounds
occur when current leaks from a conductor to
some part not intended to carry current. The
most common cause of grounds is moisture. All
circuits and their appliances are designed to be
watertight, but there may be defects in their
construction or in the method of installing them.
To prevent grounds due to moisture, all gaskets
should be kept in good condition and the covers
well secured. All caps on the receptacles should
be properly replaced. This applies especially to
fire control telephone and signal circuits. Cables
that lead outside the pressure hull are especially
subject to grounds from leakage due to submerging.
Often, sweating may occur inside the
junction or distribution boxes and these parts
must be looked after periodically. Circuits
exposed to water leaks may also suffer from
grounds. Grounds are often caused by defects
that develop in the insulation. Under some conditions,
insulating materials deteriorate very
rapidly, and they are subject also to mechanical
injury. Some of the more common causes of
such defects are:
1. Excessive heat, due to the overloading
of the circuit.
2. Excessive moisture, which causes insulation to deteriorate.
3. Oil and grease, which seriously affect
rubber and other insulating materials.
4. Acid fumes, paints, rust, and so forth,
which cause chemical decomposition of insulation.
5. Mechanical injuries, caused by making
sharp bends, kinking the wire, dragging it over
decks or through holes, or striking it while handling stores.
19A12. Short circuits. Short circuits occur
when the legs of a circuit come into direct contact
with each other, or when some low-resistance
path is established between them, thereby
allowing an abnormally large current to flow.
Short circuits are usually indicated by the
melting of the circuit fuse, and as each branch
circuit is protected with a fuse, the trouble usually
is not difficult to locate.
A short circuit may be caused by two
grounds occurring on opposite legs of a circuit.
Any of the causes of grounds may also be the
cause of a short circuit. Short circuits not due
to grounds are usually caused by faulty work,
or carelessness on the part of the electrician.
The most common of these defects in workmanship
are the failure to make proper connections
in a box, and leaving parts of the conductor
exposed. Sometimes a strain on the wire outside
the box may cause a short circuit when plugging
into a box that is not fiber bushed. Switches are
located on all receptacle boxes, and they should
be turned off before plugging in or removing a
19A13. Open circuits. Open circuits occur
when fuses blow or when circuit breakers open,
due to overloads. These overloads are usually
caused by grounds or short circuits and they
must be located and corrected. Open circuits
may also be caused by such defects as poor
connections due to improper securing, dirty
connections, or missing screws. Just enough pressure
must be used to make certain that connections
are tight without stripping threads. Broken
connections are also likely to occur when
connections are made by twisting wire or strands into
loops. This is not a good practice and should
not be resorted to except in an emergency connection
when it is to be replaced with properly
19A14. Daily ground test. The electrical
installation of a ship requires constant care to
keep it free from grounds. A daily ground test
is required. In conducting this test, the ship as
a whole is first tested for grounds, and if this
test indicates the existence of grounds, each
circuit is then tested separately. The test is
conducted by means of the ground detector on the
main control panel switchboard (see Section
19A15. Locating grounds. When the daily
ground test indicates that grounds exist on any
circuit, this circuit should be checked at once
and the trouble corrected. Each circuit is split
into sections by means of junction and distribution
boxes. To locate the defective part of the
circuit, it is necessary to break connections
between each section.
Each leg of the section is then tested with a
megger, and the section affected is soon detested.
Next, the electrical appliances on this
section are disconnected. The appliances are
then reconnected one at a time and a test made
until the affected appliances are found and the
defect corrected. Most troubles can be definitely
located, or at least located on a certain
branch, in this way. Thus, the entire circuit will
not have to be gone over completely.
19A16. Repairing circuits and appliances.
Efficiency in making repairs to electrical
circuits and appliances comes with practical
experience and knowledge of electrical principles.
In making repairs on electrical circuits,
the following precautions should be observed:
1. Disconnect the appliance; open the
circuit before beginning repairs, thus avoiding
short circuits or further trouble with tools or
2. Clean all electrical contact surfaces
3. Make tight connections.
4. Tape up the exposed part of the conductor
after making the connections, thereby
avoiding probable sources of grounds and short
5. In making wire splices, allow sufficient
wire to get enough turns for a strong splice, and
trim down the ends of the wire after splicing.
Never allow the end of the wire to project in an
6. Use rubber tape, then friction tape, and
a coat of insulating compound on a wire splice.
All three are necessary for good insulation.
7. Properly dry boxes or other electrical
appliances, and avoid moisture which might
cause corrosion and further grounds.
8. Replace covers on containers so that the
closure is watertight. Any water allowed to get
in will cause trouble.
9. Do not start work on an appliance
whose principle of operation is not known to
you. Familiarize yourself with the appliance by
referring to the manufacturer's instruction book.
10. Never place tools on top of bare electrical
conductors or terminals. If this happens
and the tools are forgotten, serious damage will
result when the circuit is closed.
11. Do not overfuse. Such a procedure results
in improper protection of appliances on
that branch of the circuit.
12. Always plan the work to be done before
starting on a job. If this is not done, there
is a possibility of ruining valuable tools and
causing further trouble. Every repair job,
especially if it is an unusual type of job, should be
sketched out first and the voltages, currents,
connection of instruments, and so forth, carefully
worked out and checked. Start repairs
only when thoroughly familiar with every detail.
An hours study before the job is started may
save many hours and many dollars in the final
13. Never install extra lights or fixtures or
make alterations in any electrical circuit without
permission from the electrical officer.
The regulations are very clear on this point. Approval
of the Bureau of Ships is required before any
major alterations may be made. Protect yourself,
your department, and possibly the safety
of the ship by not making alterations unless
they are properly authorized.
14. Never work on any electrical circuit
with which you are not thoroughly familiar,
except under proper supervision.
15. The higher the potential of a circuit,
the greater the care necessary when working on
that circuit. Always take power off the particular
part of the circuit on which you are working.
Under certain conditions 120 volts is sufficient
to cause death.
16. In replacing fuses, always stand on
some insulating material such as a rubber mat,
a dry board, or dry paper, and always use a
fuse holder made of insulating material.
17. Always handle measuring and testing
instruments with care. Almost all instruments
contain permanent magnets and must not be
handled roughly or exposed to strong magnetic
fields or vibration. Jars, heat, and proximity to
other fields will lessen the magnetism of the
permanent magnets and ruin the instrument.
Jarring will often injure the sensitive moving
18. Be careful in connecting ammeters and
voltmeters. This applies particularly to
ammeters, whose resistance is small. They will burn
up immediately if placed across a line.
19. The only safe rule in connecting up a
circuit is to first make a sketch of it. Compute
the current that will flow and indicate the
instrument necessary to make up this circuit,
showing how each should be connected. The
division officer, or one of his assistants, should
check this sketch upon its completion. No errors
will be made if proper planning precedes the
20. Before closing a motor switch, see that
the armature resistance is in. Stop the motor
by pulling the line switch. Never allow the motor
to run if it heats up to an excessive temperature,
if it sparks excessively, or if it shows other signs
of faulty operation.
21. Defects in the circuits should be repaired
as soon as they are discovered. It is much
easier to keep the electrical equipment running
perfectly by testing it daily, making repairs
where needed, than it is to allow existing
conditions to become gradually worse until
a complete overhaul is necessary.
Copyright (C) 2004 Maritime Park Association
All Rights Reserved
Version 1.10, 22 Oct 04