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 Section IX. MAIN ELECTRICAL SYSTEM
into the circuit breaker and is designed to trip. the
5-80. General
breaker when the source of voltage falls. It is so
The main control panel (fig. 2-5) of the electrical
constructed that the breaker cannot be closed until a
system is located in the engineroom, just forward of the
minimum voltage between dropout and 80 percent
main propulsion engine. It provides the controls, the
voltage is available.
instruments, resistors, circuit breakers, switches and the
b. Maintenance and Adjustment.
overload relays, trips, or under voltage release devices
(1) Remove load from undervoltage release
necessary to control the vessels electrical system. It
to be cleaned.
contains switching contactors necessary to parallel the
(2) Remove capscrews securing door on
ships service generators and to switch the power
which circuit breaker is mounted, and open the door.
requirements to shore power; individual circuit overload
(3)
Clean all dust from undervoltage
protection by means of the air circuit breakers on front
release and moving parts.
of the control panel; a ground detector for testing power
(4) Lubricate moving parts with a few drops
and lighting circuits for accidental grounds, and an
of light oil to prevent any binding in operation.
alarm system. It is a dead front panel, with all
(5) Because of the construction of the
connections made from the rear of the panel.
undervoltage release device no adjustment is
WARNING
necessary.
Before performing maintenance on the
main control panel components, all
5-83. Overload Trip Attachment
precautions must be taken to assure
a. General. The overload trip device trips the
safety, and deck must be dry. Use test
circuit breaker whenever the current in the circuit
instruments, and work from front of
exceeds the overload setting.
panel when possible, to avoid injury.
b. Maintenance and Adjustment.
Always secure load to instrument
(1) Remove load to overload trip to be
undergoing maintenance as directed
cleaned.
in the maintenance paragraphs below.
(2) Remove capscrews which hold door on
which circuit breaker' is mounted, and open door.
5-81. Circuit Breakers
(3) Clean all dust from overload trip and
a. General. The circuit breaker installed on the
moving parts.
main panel performs two basic functions: to carry the
(4) To adjust the trip. setting, loosen the
rated current, and to interrupt currents at or below the
calibrating knob, place the pointer at the desired setting,
interrupting capacity. The first function is performed by
and retighten the calibrating knob.
the main contacts which are made of copper and heavily
silver plated to produce low contact resistance. To
5-84. Shunt Trip
perform the second function and protect the main
a. General. The shunt trip is mounted on the
contacts, arcing contacts are provided. These contacts
right side of the breaker and is used for tripping the
mate first in closing, and break last in opening, thus
breaker by means of a pushbutton.
bearing the full force of any arc formed during the
b. Maintenance and Adjustment.
opening or closing operation.
(1) Remove load to shunt trip to be cleaned.
b. Maintenance and Adjustment.
(2) Remove capscrews which hold door on
(1) The safety of personnel and protection
which circuit breaker is mounted, and open door.
of vital equipment often depends on correct functioning
(3) Clean all dust from shunt trip and
of circuit breakers. Breakers must be kept clean and
moving parts.
operate freely.
NOTE
(2) Secure load to circuit breaker to be
The shunt trip coil is immediately cut
cleaned.
out of the circuit when the breaker
(3) Remove capscrews securing door on
opens.
which circuit breaker is mounted, and open door.
(4) Because of the simplicity of construction
(4) Clean all dust from circuit breaker and
no adjustment is necessary.
moving parts.
(5) Lubricate moving parts with a few drops
5-85. Auxiliary Switches
of light oil.
a. General. The rotary type auxiliary switches are
composed of a rotor, mounted on the main operating
5-82. Undervoltage Release Device
shaft of the breaker, which rotates with the shaft.
a. General. The undervoltage release is built
b. Maintenance and Adjustment.
(1) Remove load to auxiliary switch to be
cleaned.
5-168
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