Distribution Boxes

predetermined manner, the operation of the dc or ac

such as cracks in the material and separation at the

motor to which it is connected. Preventive mainte-

seams. Ventilation opening located to permit water to

nance of motor controllers should be accomplished

discharge onto electrical equipment, insufficient

while consulting the applicable PMS card. Trouble-

insulation overhead to prevent sweating, need for

shooting and corrective maintenance of motor

dripproof covers and spray shields, and location of

controllers is discussed in depth in Interior

water piping and flanges where leakage could spray

Communications Electrician, volume 2, NAVEDTRA

onto switchboards and other gear are examples of

12161.

installations that could cause casualties. Action should

be initiated to have unsatisfactory conditions

corrected.

MAINTENANCE AND REPAIR OF

POWER SUPPLIES

Distribution Boxes

Wiring distribution boxes (fused), with and without

Now that we have discussed the different types of

switches, that feed vital circuits should be checked

power distribution systems and switchboards and the

annually. Tighten fuse clip barrel nuts and terminal

maintenance of switchboards, we will discuss the

connections. On anew ship and after a major overhaul,

maintenance and repair of two of the most common

tighten and prick punch loose bus bar nuts on the backs

power supplies: motor generators and static inverters.

of insulating bases.

MOTOR GENERATORS

The phosphor-bronze fuse clip and supplementary

bent-wire fuse retainer have been superseded by a steel

Under normal conditions, the motor generator set

copper-clad silver-plated fuse clip. The steel fuse clips

and control equipment require inspection and cleaning

do not require fuse retainers to prevent dislodgement

as designated by the PMS MRCs. When the motor

of fuses under shock and vibration. The wire fuse

generator is inspected, cleanliness, brush operation,

retainers impose a hazard of possible accidental

condition of brushes and commutator, bearing tempera-

dislodgement and falling into bus work to cause short

ture, and vibration should be observed.

circuits. To eliminate this hazard on both vital and

The acceptable methods of cleaning motors and

nonvital circuits that require frequent removal of

generators involve the use of wiping rags or cloths,

fuses, and where difficulties occur with loosening of

suction, low-pressure air, and solvents.

Wiping with a clean, lint-free, dry rag (such as

existing phosphor-bronze fuse clips and wire fuse

retainers, steel copper-clad silver-plated fuse clips

cheesecloth) is effective for removing loose dust or

should be used. Do not remove the wire retainers until

foreign particles from accessible parts of a machine.

the new steel fuse clips are on board for substitution.

When wiping, do not neglect the end windings, mica

Tighten the fuse-clip barrel nut until the arch in bottom

cone extensions at the commutator of dc machines,

of the steel fuse clip is drawn flat.

slip-ring insulation, connecting leads, and terminals.

The use of suction is preferred to the use of com-

Emergency Switchboards

pressed air for removing abrasive dust and particles

from inaccessible parts of a machine because it lessens

Emergency switchboards should be tested regu-

the possibility of damage to insulation. If a vacuum

larly, according to the instructions on the switchboard,

cleaner is not available for this purpose, a flexible tube

to check the operation of the ABT equipment and the

attached to the suction side of a portable blower will

automatic starting of the emergent y generator.

make a suitable vacuum cleaner. Always exhaust the

All other preventive maintenance should be

blower to a suitable sump or overboard. Whenever

performed according to the applicable PMS card.

possible, remove grit, iron dust, and copper particles by

Remember, when you are conducting tests or trouble-

suction methods.

shooting equipment, the first thing you should do is

Clean, dry, compressed air is effective in removing

consult your PMS schedule. By doing this, you will

dry, loose dust and foreign particles, particularly from

find information to assist you.

inaccessible locations such as air vents in the armature.

Use air pressure up to 30 pounds per square inch (psi)

to blow out motors or generators of 50 horsepower (hp)

MOTOR CONTROLLERS

or 50 kilowatts (kW) or less; use pressure up to 75 psi

to blowout higher-rated machines. Where airlines carry

By definition, a motor controller is a device (or

higher pressure than is suitable for blowing out a

set of devices) that serves to govern, in some

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