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19
INTERIOR COMMUNICATION SYSTEM
MAINTENANCE
 
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 cause ignition.

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 week.

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 week.

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.

 
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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 A-2 circuits.

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 short circuit.

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 circuits.

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 portable connection.

19A13. Open circuits. Open circuits occur when fuses blow or when circuit breakers open,

 
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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 soldered lugs.

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 3C4).

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 equipment.

2. Clean all electrical contact surfaces properly.

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 circuits.

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 exposed position.

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.

 
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An hours study before the job is started may save many hours and many dollars in the final outcome.

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 coils.

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 actual work.

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.

 
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