(a)
When the left generator is operating with its generator circuit breaker (GCB) open, a red L GEN warning light on left generator power panel P31 is on. If the left GCB is closed, a red L 115 VAC warning light will also be on. The L 115 VAC warning light is on P31 panel. The right main AC bus functions similarly. The components are on right generator power panel P32.
(b)
The main AC buses can also be powered by the APU generator or external power. This power is connected through contactors to the AC tie bus. Three-phase bus tie breakers connect the power to the main AC buses. Three red warning lights will be on: EXT BUS TIE on P34 panel, LEFT TIE BUS on P32 panel, and if the APU generator is used, a red HOT BUS WARN light on P34 will also be on.
(c)
Each main AC bus is divided into four sections to distribute power. Each section is supplied through a three-phase thermal circuit breaker. If a fault occurs, the breaker isolates the faulted section from the other sections.
(d)
The first two sections of both main buses are in overhead cicuit breaker panel P11. The third section of both buses is divided between P6 and P11 panels. The fourth section of the left bus is in left misc. electrical equipment panel P36. The fourth section of the right bus is in right misc. electrical equipment panel P37.
(e)
EICAS computers monitor main AC bus status.
(2)
Utility Buses and Galley Buses (Figs. 3, and 4)
(a) The left and right utility buses supply single-phase and three-phase power to non-essential loads. Power to these loads is removed if load reduction is needed. The left utility bus is located in P36 panel, and the right utility bus is located in P37 panel.
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LEFT GEN
AIRPLANES WITH LEFT UTIL
BREAKER
BUS RELAY GENERATOR
HYDRAULIC MOTOR
Main AC Bus SchematicFigure 2
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MAINTENANCE MANUAL
H12309
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MAINTENANCE MANUAL
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MAINTENANCE MANUAL
R UTIL PWR
R UTIL PWR OFF
GALLEYPOWER
28V DCR BUS GALLEY
GALLEY MID FWD
POWERTRIP 28V DC
ON LEFT BUS
RIGHT UTILITY CTR BUS CTR BUS
GALLEYBUS SWITCH RIGHT UTILITY GALLEY GND
CLOSE
AFT PWR PWR
BUS RESET RLY CR2
LOAD SHED RELAY
R GEN CIRCUIT28V DC
BREAKER
GLR 2 RESETENG START LDSHED RESET
LEFT BUS GLR 3 RESET
L UTIL PWR
GLR 1 RESETOFF L UTIL PWRP11 ALR LOAD SHED
BUS POWER TRIP
CONTROL UNIT
CR1
L BUS TIE
L BUS TIE
TRIP
ON
GND START
CLOSE LEFT UTILITY CTR BUS
CTR BUS
BUS SWITCH LEFT UTILITYL ENG START
PWR CLOSE PWR
T RLY 2
APU GEN BUS RESET RLY
BREAKER D
L GEN CIRCUIT 3 SEC BREAKER GND GALLEYLOAD SHED CONTROLRELAY
ELEC SYSTEMS CONTROL PANEL
GND START
VALVE OPENR ENG STARTRLY 2
APU BLEED AIR GNDVALVE CONTROL RLY
TRIP
AIR T
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