(2)
The P6 panel contains many of the thermal circuit breakers for load distribution, standby loads, fuel systems, and fire extinguishing systems. The P6 panel is located on the lower right side of the flight deck aft section.
(3)
DC load distribution circuit breakers are located primarily in two centers in the lower forward E/E bay and in the flight deck. The majority of circuit breakers in the lower E/E bay are mounted in the P180 dc power distribution panel.
(4)
DC main bus fault isolation is provided by the associated TRU input 3-phase thermal circuit breaker and by the associated dc tie bus breaker.
(5)
Remote control circuit breakers (RCCBs) are used for protection of the dc feeders from the P180 power shield to the P6 panel. In addition, RCCBs are used to supply power to the battery buses/main static inverter from dc bus 3 and the main battery hot bus. Individual loads which require inflight resettability have their thermal circuit breakers located in the P6 and P7 panels. Nonessential loads are distributed between the P6 and P180 panels. The RCCBs are resettable from the flight deck via their control thermal circuit breakers located in the P6 panel.
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24-61-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
P180
28-Volt DC Power Distribution Simplified SchematicFigure 1
A
747-400
MAINTENANCE MANUAL
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24-61-00
ALL ú ú 02 Page 2 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
(6)
Each main dc load distribution bus, which supplies power to individual load equipment is divided into two sections (P6 and P180) due to source equipment location and load distribution requirements.
(7)
All flight essential electrical loads have redundancy and are distributed on the nonsheddable dc buses.
(8)
Nonessential loads are connected to bus sections which can be de-energized (shed) automatically or manually, thus providing added assurance of adequate power to essential loads during abnormal operating conditions.
(9)
Loads such as cargo handling which are required only on the ground are connected to the ground handling bus. This bus is arranged such that it cannot be energized in flight.
(10)
The three-position (BAT-AUTO-OFF) rotary STANDBY POWER switch and the pushbutton BATTERY switch provide manual control of the battery buses in the unlikely event that the automatic transfer system has failed. During normal operation, the switches are in the AUTO and IN position, respectively. If the STANDBY POWER switch is moved to the BAT position and the BATTERY switch is ON, then the main/APU battery buses will be transferred to the main/APU battery hot buses, respectively.
(11)
The battery buses and main static inverter are supplied from dc bus No. 3, if it is energized, provided the STANDBY POWER switch is in the OFF or AUTO positions. If dc bus No. 3 is de-energized, the main battery bus and the inverter will be supplied from the main battery hot bus and the APU battery bus will be supplied from the APU battery hot bus. The BATTERY switch will be in the ON position during normal operation.
(12)
Power for each ground handling bus is supplied from a ground power TRU.
(13)
Input power for each ground power TRU is supplied from the ac ground handling bus.
(14)
Bus isolation against faults and overloads is provided by the ground power TRU input 3-phase circuit breakers.
(15)
The dc ground handling buses and the associated load distribution circuit breakers are located in the lower forward E/E equipment bay P414 power distribution center-left.
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