B.  The battery bus receives power normally from T-R No. 3. When T-R No. 3 is not operating, the battery bus is connected to the hot battery bus.
(1)  
On AT CN-RMI thru CN-RML; CA B2501 thru B2503; IDO 601; OI G-BGTW thru G-BJBJ; ZD G-AVRL thru G-BJCV,  during normal operation, the dc standby bus is supplied power by the No. 1 dc bus (Fig. 2). Should a complete power failure occur, dc bus No. 1 is de-energized, the standby power transfer relay (R37) relaxes, the battery is automatically connected to the battery bus and the dc standby bus. The sequence for this operation is: the battery switch is in the ON position, the battery transfer relay (R2) relaxes when dc bus No. 3 goes dead, the battery bus relay (R1) closes and energizes the battery bus and the standby power transfer relay No. 1 (R36) closes.

(2)  
On AT ALL EXCEPT CN-RMI thru CN-RML; CA ALL EXCEPT B2501 thru B2503; IDO ALL EXCEPT 601; OI ALL EXCEPT G-BGTW thru G-BJBJ; ZD ALL EXCEPT G-AVRL thru G-BJCV,  dc standby loads are connected to the battery bus. Upon loss of TR3 output power, battery transfer relay R1 energizes automatically connects battery bus to the battery. The battery switch must be set to ON and the STANDBY POWER switch must be set to AUTO for automatic transfer to occur. If the automatic sequence fails, the STANDBY POWER switch is set to BAT. Battery bus relay manual R326 closes and battery bus is connected to the battery.

C.  The radio and other electronic equipment dc power is distributed from isolated buses connected to dc buses No. 1 and No. 2. Protection is provided with thermal circuit breakers. Circuit breakers C27 and C31 separate dc buses No. 1 and No. 2 respectively from the system and therefore, isolate the electronic load buses (Fig. 2.). Equipment subject to control by the flight crew is connected to the buses, which are energized only when the No. 1 or No. 2 master electronic switches (S17) and S18) are in the ON position. This distinction is indicated by showing one branch of the bus as switched and the other as unswitched (Fig. 2).
507 
Jun 20/83  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  24-55-0 Page 3 

EFFECTIVITY 
AT  CN-RMI THRU CN-RML 
CA  B2501 THRU B2503 
IDO  601 
OI  G-BGTW THRU G-BJBJ 

K91271
DC Power Distribution  556 
24-55-0  Figure 2 (Sheet 1)  Jan 20/83 
Page 4 

BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EFFECTIVITY 
CA B2501 THRU B2503 
IDO 601 
NU JA8443 THRU JA8475 
TH HS-TBA THRU HS-TBD 

K91311
5C8  DC Power Distribution 
Jun 20/83  Figure 2 (Sheet 2)  24-55-0 
Page 5 

BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

EFFECTIVITY
CA ALL EXCEPT B2501 THRU B2503 IDO ALL EXCEPT 601

DC Power Distribution  5C8 
24-55-0  Figure 2 (Sheet 3)  Jun 20/83 
Page 6 

BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

H34799
501  DC Power Distribution Component Location 
Aug 15/68  Figure 3  24-55-0 
Page 7 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.