AUX 
PWR 
BAT BUS
UP SOFTWARE
BUS PWR
HARDWARE 
DIGITALCOMM 
CONTROL UNIT P6 
LINK 28V DCR BUS 
APU GEN CONTBUS PWR CONT UNIT UNIT SECONDARY 
BUS POWER CONTROL UNIT
P11
External Power Schematic
Figure 2
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757 
MAINTENANCE MANUAL
 A. Functional Description
______________________
 (1)  
Connecting external power to the EPR turns on the red EXT PWR HOT BUS warning light on P34 panel. The DC interlock circuit to the BPCU is completed, and the BPCU checks external power quality. If external power voltage, frequency, and phase sequence are correct, the white AC PWR CONNECTED light on P30 panel will come on. The white EXT PWR AVAIL light on M10063 electrical system control panel will be on. If external power is not selected, the clear PWR NOT IN USE light on P30 panel will be on.
 (2)  
The momentary action EXT PWR switch on M10063 panel controls the system. Pressing the switch once turns on the system. The BPCU causes the auxiliary power breaker and generator circuit breakers to open, if previously closed. The BPCU energizes the EPC. The EXT PWR AVAIL and ON lights on M10063 panel will be on. The AC PWR CONNECTED light on P30 panel will be on. The PWR NOT IN USE light on P30 panel will be off. Pressing the EXT PWR switch again removes external power.
 (3)  
If the engines are started, the EPC will open when engine speed is sufficient to produce correct quality power. The generator circuit breakers close, providing power from the main generators. Pressing the EXT PWR switch will switch external power to the buses.
 (4)  
If external power current exceeds 330 | 70 amps/phase, the BPCU will disconnect external power.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
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757 FAULT ISOLATION/MAINT MANUAL 
EXTERNAL POWER 
COMPONENT  SHT 102 FIG.  QTY  ACCESS/AREA  REFERENCE  
AUXILIARY POWER, C905 BREAKER - (REF 24-22-00, FIG. 101)  
CIRCUIT BREAKER  -- FLT COMPT, P6 
 BUS PWR CONT UNIT, C809  1  6B4  * 
CIRCUIT BREAKER  -- FLT COMPT, P11  
BPCU SEC, C803  1  11R32  *  
CIRCUIT BREAKER  -- 119BL, MAIN EQUIP CTR, P34  
EXTERNAL POWER, K114 GROUND POWER BPCU, C320CONTACTOR - (REF 31-01-34, FIG. 101)  1  34M6, SECT A  *24-41-01  
LIGHT - AC CONNECTED, L4 -- 1  120AR, P30  *  
LIGHT - HOT BUS WARNING, L15  -- 1  119BL, P34  *  
STANDBY POWER CONTROL, M10062 PANEL - (REF 24-33-00, FIG. 101) ELECTRICAL POWER SYSTEM CONTROL, M10063 PANEL - (REF 24-22-00, FIG. 101) LIGHT - POWER NOT IN USE, L5  -- 1  120AR, P30  * 
 POWER TIE BUS, T116 GRND POWER CURRENT, T122 CURRENT DIFFERENTIAL PROTECTION EXTERNAL TRANSFORMER - (REF 31-01-34, FIG. 101) RECEPTACLE - EXTERNAL POWER, D1718  -- 1  120AR, P30  24-41-02  
APU GENERATOR CONTROL, M143 LEFT GENERATOR CONTROL, M144 RIGHT GENERATOR CONTROL, M146UNIT - (REF 24-22-00, FIG. 101) UNIT - BUS POWER CONTROL, M116 -- 1  821, FWD CARGO COMPT, E5-3  24-41-03 
* SEE THE WDM EQUIPMENT LIST
External Power - Component Index 
Figure 101
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 ú  Dec 20/90 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A
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FAULT ISOLATION/MAINT MANUAL
P34 PANEL  
MAIN EQUIPMENT  
 
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