.
DC standby bus

.
battery bus.

Copyright . The Boeing Company. See title page for details.
Electrical -Controls and Indicators 737 Flight Crew Operations Manual

STANDBY POWER Switch
AUTO (guarded position) –
.
In flight, or on the ground, and AC transfer busses powered:

.
AC standby bus is powered by AC transfer bus 1

.
DC standby bus is powered by TR1, TR2 and TR3

.
In flight, or on the ground, loss of all AC power

.
AC standby bus is powered by battery through static inverter

.
DC standby bus is powered by battery

.
Battery bus is powered by battery. OFF (center position) –

.
STANDBY PWR OFF light illuminates

.
AC standby bus, static inverter, and DC standby bus are not powered. BAT (unguarded position) –

.
AC standby bus is powered by battery through static inverter

.
DC standby bus and battery bus are powered directly by battery.

Copyright . The Boeing Company. See title page for details.
6.10.10  September 27, 2004

Electrical -Controls and Indicators
Ground Power Panel and Bus Switching Panel

Ground Power Available (GRD POWER AVAILABLE) Light
Illuminated (blue) – ground power is connected and meets airplane power quality standards.

Ground Power (GRD PWR) Switch
Three position switch, spring–loaded to neutral
OFF – disconnects ground power from AC transfer busses.
ON – if momentarily moved to ON position and ground power is available:

.
removes previously connected power from AC transfer busses

.
connects ground power to AC transfer busses if power quality is correct.

TRANSFER BUS OFF Lights
Illuminated (amber) – related transfer bus is not powered.
Copyright . The Boeing Company. See title page for details.
Electrical -Controls and Indicators 737 Flight Crew Operations Manual

SOURCE OFF Lights
Illuminated (amber) – no source has been manually selected to power the related transfer bus, or the manually selected source has been disconnected
.  if a source has been selected to power the opposite transfer bus, both
transfer busses are powered.

Generator Off Bus (GEN OFF BUS) Lights
Illuminated (blue) – IDG is not supplying power to the related transfer bus.

Generator (GEN) Switches
Three position switch, spring–loaded to neutral.
OFF – disconnects IDG from related AC transfer bus by opening generator circuit breaker.
ON – connects IDG to related AC transfer bus by disconnecting previous power source and closing generator circuit breaker,

BUS TRANSFER Switch
AUTO (guarded position) – BTBs operate automatically to maintain power to AC transfer busses from any operating generator or external power
.  DC cross tie relay automatically provides normal or isolated operation as
required.

OFF – isolates AC transfer bus 1 from AC transfer bus 2 if one IDG is supplying power to both AC transfer busses
. DC cross tie relay opens to isolate DC bus 1 from DC bus 2.

APU Generator Off Bus (GEN OFF BUS) Light
Illuminated (blue) – APU is running and not powering a bus.

APU Generator (GEN) Switches
Three position switch, spring–loaded to neutral.
OFF –
.
APU generator powering both AC transfer busses

.  
moving a single APU GEN switch to OFF illuminates related SOURCE OFF light. APU continues to power AC transfer busses

.  
subsequently moving other APU GEN switch to OFF disconnects APU generator from tie bus and removes APU power from AC transfer busses

.  
APU generator powering one AC transfer bus; IDG powering one AC
transfer bus

Copyright . The Boeing Company. See title page for details.
6.10.12   September 26, 2003

Electrical -Controls and Indicators 737 Flight Crew Operations Manual
.  moving related APU GEN switch to OFF disconnects APU generator from tie bus and AC transfer bus. IDG powers AC transfer busses.
ON –
.  
Neither AC transfer bus powered by IDG – moving a single APU GEN
switch to ON:

.  
connects both AC transfer busses to the APU generator

.  
disconnects external power, if connected

.  opposite SOURCE OFF light illuminates until the other APU GEN switch is moved to ON.
.  
Both AC transfer busses powered by IDGs – moving an APU GEN switch ON:

.
powers the related AC transfer bus from the APU generator . other AC transfer bus continues to receive power from the IDG.
　
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