H21500 H21506 H80653 H21524
500  AC Electrical Bus Diagram 
May 15/67  Figure 1  24-50-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Load Control Center (P6) Component Location  500 
24-50-0  Figure 2 (Sheet 1)  May 15/67 
Page 4 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

556  Load Control Center - Right (P6) Component Location 
Jun 20/83  Figure 2 (Sheet 2)  24-50-0 
Page 5 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Load Control Center-Right (P6) Component Location  525 
24-50-0  Figure 2 (Sheet 3)  Feb 15/71 
Page 6 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

General

A.  Three-phase 115-volt ac power is supplied by two engine generators and the APU generator in flight, and by a 3-phase 115 volt ac external source or the APU when the airplane is on the ground. Three-phase power from these four sources is distributed from the control cabin in the aircraft through bus systems located mainly in two panels, the load control center-right P6 and the load control center-left P18 and controlled from the forward and aft overhead panels P5. The load control centers P6 and P18 contain power distribution busses supplying power from the No. 1 and No. 2 generator busses, and from the No. 1 and No. 2 transfer busses. (Fig. 1) The load control centers panel P6 and panel P18 contain the contactors, relays, and the circuit breakers supplying power from various busses. Panel P6-11 contains transfer bus No. 1 and the alternate or transfer bus No. 2, which are load busses connected to generator bus No. 1 along with the 3-phase No. 1 section X portions. Power delivered from the three generators including the APU and from the external power source is electrically switched by circuit breakers C801, C802, C803 and the external power contractor R8, respectively. Circuit breakers C801 and C802 and the external power contactor R8 are located in the right hand forward compartment, outboard nose wheel well. A 3-phase tie bus permits connections to the four sources while using the two bus and wiring systems. Except for the power diverted by the No. 1 and No. 2 galley relays R61 and R62 all of the incoming power is distributed to busses terminating in large load relays or in miscellaneous circuit breaker panels P6-4, P6-3, P6-2 and P6-1 progressing upward as shown on figure 3. The load control center panels P6-11 and P6-12 are the circuit breaker locations for generators No. 1 and No. 2 respectively. Relays R3, R4, R23, R24 and R68 are transfer contactors used to change power sources and the switch operating loads to and from the above mentioned distribution busses. (Fig. 2) With the No. 1 transfer relay R3 in the normal position and generator No. 1 supplying power through circuit breaker C819 shown on figure 2, the No. 1 pump relay R23 will be conducting power from the normal route through C830. When the No. 1 generator breaker opens however, R3 transfers the No. 1 transfer bus to the No. 2 generator bus, therefore the pump relay R23 must transfer to obtain power from the alternate source through C831.
502 
Nov 15/67  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  24-51-0 Page 1 

H29734 H34650
Main 115 Volt AC Power Distribution Bus Diagram (Single Line)  502 
24-51-0  Figure 1  May 15/67 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

5B6  115 Volt AC Power Distribution Diagram 
Jun 20/83  Figure 2 (Sheet 1)  24-51-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

B.  The transfer relays are normally held in the preferred positions permitting the respective transfer buses to be energized by the corresponding generator buses. An alternate position and a center off position are provided (Fig. 1). In the event that power is lost from the No. 1 generator, a signal from the No. 2 GCU will switch the No. l transfer relay to the alternate position allowing the No. 2 generator to energize the No. 1 transfer bus and provide power for essential No. 1 generator loads. This signal is a function of proper generator breaker and BTB position and is time-delayed to eliminate nuisance transfers. If power is lost from the No. 2 generator, a similar transfer will take place so that the No. 1 generator will supply power for essential No. 2 generator loads.
　
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