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 TM 55-1925-273-10-1
0034 00
EMERGENCY SWITCHBOARD
The emergency switchboard is located in the emergency generator room and normally receives 440 Vac primary power from
the main switchboard through the bus tie. Refer to figure 2 for a block diagram of the emergency switchboard. The emer-
gency switchboard bus tie provides 440 Vac to the emergency switchboard. Upon loss of the ship's service power from the
main switchboard, a bus tie transfer breaker located within the emergency switchboard isolates the emergency switchboard
and provides automatic or manual starting of the emergency generator. A voltmeter, ammeter, and a frequency meter provide
the power monitoring capability.
A main switchboard bus tie circuit breaker and feedback switch permit the distribution of emergency power (440 Vac) to the
main switchboard. The EDG circuit breaker is prevented from being closed by an interlock system when primary power is
being provided through the bus tie circuit breaker. Power distribution (440 Vac) is accomplished through circuit breakers on
the switchboard.
TRANSFORMERS
The LT contains three step-down transformers that are located in the engine room and convert 440 Vac to 220/110 Vac. The
transformers provide 120 Vac for the engine room load center. The LT also contains three step-down transformers, located
in the emergency generator room (overhead), that provide 120 Vac power to the EMERG LOAD CTR DISTRIBUTION
PANEL.
DISTRIBUTION PANELS
There are several distribution panels located throughout the LT. The following paragraph describes the essential distribution
panels used within the alternating current electrical system. The distribution panels house the circuit breakers and the fuses
that control and protect the circuits throughout the vessel.
The engine room load center distribution panel supplies 120 Vac to several power panels, and workshop equipment. The
EMERG LOAD CTR DISTRIBUTION PANEL provides 120 Vac emergency power distribution to numerous emergency
distribution panels, in addition to the battery chargers. The 220/110 V distribution panel provides power distribution for the
galley, the crew's mess, and laundry spaces. The ENG RM DIST PNL NO. 4 provides power distribution for the engine
room equipment, the welder, refrigerated stores controls, emergency generator strip heater and emergency switchboard
heater. The radio room electronics distribution panel provides 120 Vac power to the communications equipment and battery
charger.
MOTOR CONTROLLERS
There are eight types of motor controllers that provide the start and stop function of the motor and overload protection for the
motor, as well as the status of the motor operation via the power available indicators and motor operating speed indicators.
DC ELECTRICAL SYSTEM
The direct current electrical system consists of the battery chargers, battery banks, and distribution panels.
STORAGE BATTERIES
Six independent 24 Vdc battery banks are provided. Refer to figure 3 for a block diagram of the battery power distribution
system. One set of batteries provides starting power for the EDG engine. The second set provides starting power for SSDG
1. The third set of batteries provides power for the general alarm system. A fourth set of batteries provides power to the radio
room DC panel, which supplies selected Communication, Electronic, and Navigation (CEN) equipment. Set five provides
power (24 Vdc) for the machinery plant monitoring system and engine control. The sixth set of batteries provides 24 Vdc for
the Reverse Osmosis Water Purification Unit (ROWPU).
BATTERY CHARGERS
Battery chargers for each battery bank are provided. The battery chargers are supplied 120 Vac from the emergency load
center distribution panel (see figure 2 for the emergency switchboard block diagram). One charger is for the SSDG 1, and the
other charger is for the machinery plant monitoring system and engine control.
0034 00-4
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