Rheostats and Resistors

Rheostats and Resistors

else that will reduce downtime. Remember, you are only

looking for a temporary replacement.

Be certain the ventilation of rheostats and resistors

is not obstructed. Replace broken or burned-out

SWITCHBOARD MAINTENANCE

resistors. Temporary repairs of rheostats can be made by

bridging burned-out sections when replacements are not

Another duty of an IC Electrician is the maintenance

available. Apply a light coat of petrolatum to the

of the power distribution systems assigned to your

faceplate contacts of rheostats to reduce friction and

division. Normally, the required inspections and

wear. Be certain no petrolatum is left in the spaces

cleanings are outlined on maintenance requirement

between the contact buttons, as this may cause burning

cards (MRCs). When the inspection and cleaning is due,

or arcing. Check all electrical connections for tightness

you often think only of the main IC switchboard. The

and wiring for frayed or broken leads.

small local IC switchboards located in the engineering

spaces and remote sections of the ship are forgotten.

Instruments

Auxiliary IC panels may have their own MRCs. You, as

a supervisor, should make sure all power panels receive

The pointer of each switchboard instrument should

the attention needed.

read zero when the instrument is disconnected from the

circuit. The pointer may be brought to zero by external

INSPECTION AND CLEANING

screwdriver adjustment.

At least once a year and during overhaul, each

CAUTION: This should not be done unless proper

switchboard propulsion control cubicle, distribution

authorization is given. Repairs to the switchboard

panel, and motor controller should be de-energized and

instruments should be made only by the manufacturers,

tagged out for a complete inspection and cleaning of all

shore-repair activities, or tenders.

bus equipment. Inspection of the de-energized

equipment should not be limited to visual examination

Fuses

but should include grasping and shaking electrical

connections and mechanical parts to be certain that all

Be certain fuses are the right size; clips make firm

connections are tight and that mechanical parts are free

contact with the times; lock-in devices (if provided) are

to function. Be certain no loose tools or articles are left

properly fitted; and all connections in the wiring to the

in or around switchboards or distribution panels.

fuses are tight.

Check the supports of bus work to be certain the

Control Circuits

supports will prevent contact between bus bars of

opposite polarity or contact between bus bars and

grounded parts during periods of mechanical shock.

Control circuits should be checked to ensure circuit

continuity and proper relay and contactor operation.

Clean the bus work and the creepage surfaces of

insulating material; be certain creepage distances

Because of the numerous types of control circuits

installed in naval ships, it is impractical to set up any

(across which leakage currents can flow) are ample to

prevent arcing. Bus bars and insulating materials can be

definite operating test procedures in this training

manual. In general, certain control circuits, such as those

cleaned with dry wiping clothes and a vacuum cleaner.

Make sure the switchboard or distribution panel is

for starting motors or motor-generator sets, or voltmeter

switching circuits are best tested by using the circuits as

completely de-energized and will remain so until the

work is completed; avoid cleaning live parts because of

they are intended to operate under service conditions.

the danger to personnel and equipment.

Protective circuits, such as overcurrent, reverse

power, or reverse current circuits, usually cannot be

The insulated front panels of switchboards can be

cleaned without de-energizing the switchboard. These

tested by actual operation because of the danger

panels can usually be cleaned by wiping with a dry cloth.

involved to the equipment. These circuits should be

However, a damp, soapy cloth can be used to remove

visually checked and, when possibe, relays should be

grease and fingerprints. Then wipe the surface with a

operated manually to be certain the rest of the protective

cloth dampened in clear water to remove all soap and

circuit performs its intended functions. Exercise

dry with a clean, dry cloth. Cleaning cloths must be rung

extreme care not to disrupt vital power service or

out thoroughly so no water runs down the panel. Clean

damage electrical equipment. Normally these checks

a small section at a time and then wipe dry.

and inspections are outlined on MRCs.

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