With the battery switch offand no GPU hooked up, these buses are powered.

When any of the followingdoors are opened, the GroundHandling Bus is energized through the Battery Transfer Relay.

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

1. Cargo Door Access Panel2. Refueling Panel3. Main Cabin Door4. Auxiliary Hydraulic Pump

Push Button is depressed.

BTR

If you walk into the cockpit and observe a GREEN AVAILlight on the main electrical panel, these buses are now powered.

AVAIL

SHED

SHED

EXT PWR DC GEN 2DC GEN 1

AC BUS 2

INV 1 INV 2

01

2

1

2DC

CHDCH

ESS BUS

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

STBY BUS

EMER BUS

DC BUS 2

OFF

ON

OVRD

BAT

MAIN BATCHG

EMER BATCHG

DC BUS 1

AC BUS 1

EXTERNALPOWER

EGHR

When the GPU is plugged in, theExternal Ground Handling Relaycloses taking priority over the BusTransfer Relay. The BTR then opens.

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

DC SVCEBUS

If the DC SERVICE BUS pushbutton is depressed on theflight attendant panel, thenthe DC SERVICE BUS is powered through the Service Bus Transfer Relay.

ON

GND SVCE BUS

PASS LAV CAPT LAV CARGOEMER

LT

CALLS SMOKE

GALLEY LAV

LAT

PASS DIM

UPR

PASS ENTR

AFT

CARGO

READ

LT VENT

ACDC

The GPU is now poweringthe Ground Handling Bus and the DC Service Bus.

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

SBTR

Now we turn on the Main Battery Toggle Switch.

AVAIL

SHED

SHED

EXT PWR DC GEN 2DC GEN 1

AC BUS 2

INV 1 INV 2

01

2

1

2DC

CHDCH

ESS BUS

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

STBY BUS

EMER BUS

DC BUS 2

OFF

ON

OVRD

BAT

MAIN BATCHG

EMER BATCHG

DC BUS 1

AC BUS 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

SBTR

Now we turn on the Main Battery Toggle Switch.

AVAIL

SHED

SHED

EXT PWR DC GEN 2DC GEN 1

AC BUS 2

INV 1 INV 2

01

2

1

2DC

CHDCH

ESS BUS

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

STBY BUS

EMER BUS

DC BUS 2

OFF

ON

OVRD

BAT

MAIN BATCHG

EMER BATCHG

DC BUS 1

AC BUS 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

SBTR

Now we turn on the Main Battery Toggle Switch.

AVAIL

SHED

SHED

EXT PWR DC GEN 2DC GEN 1

AC BUS 2

INV 1 INV 2

01

2

1

2DC

CHDCH

ESS BUS

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

STBY BUS

EMER BUS

DC BUS 2

OFF

ON

OVRD

BAT

MAIN BATCHG

EMER BATCHG

DC BUS 1

AC BUS 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

SBTR

Now with the main batteryon, these buses are powered.

FAULTFAULT AVAIL

SHED

SHED

DC GEN 2DC GEN 1

01

2

1

2DC

CHDCH

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

DC BUSOFF

DC BUSOFF

BUSOFF

INVFAULT

BUSOFF

EXT PWR

EMER BATCHG

EMER BUS ESS BUS

STBY BUS

AC BUS 2AC BUS 1

INV 1

DC BUS 1

OFF

ON

OVRD

BAT

MAIN BATCHG

INV 2

DC BUS 2

DC EMER BUS

DC STBY BUS

DC ESS BUS

HMBTCHEBTC

SBTC

HBTC

INV 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

SBTR

HEBTC = Hot Emergency Bus Transfer Contactor

HMBTC = Hot Main Bus Transfer Contactor

SBTC = Standby Bus Transfer Contactor

HBTC = Hot Battery Transfer Contactor

115 VAC SBY

26 VAC SBY

When the external power pushbutton is depressed, these buses are powered.

FAULTFAULT AVAIL

SHED

SHED

DC GEN 2DC GEN 1

01

2

1

2DC

CHDCH

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

DC BUSOFF

DC BUSOFF

BUSOFF

INVFAULT

BUSOFF

EXT PWR

EMER BATCHG

EMER BUS ESS BUS

STBY BUS

AC BUS 2AC BUS 1

INV 1

DC BUS 1

OFF

ON

OVRD

BAT

MAIN BATCHG

INV 2

DC BUS 2

DC EMER BUS

DC STBY BUS

DC ESS BUS

HMBTCHEBTC

SBTC

HBTC

INV 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

Hot Main Battery

Hot Emergency Battery

BTR

SBTR

115 VAC SBY

26 VAC SBY

SDTC

When the external power pushbutton is depressed, these buses are powered.

FAULTFAULT AVAIL

SHED

SHED

DC GEN 2DC GEN 1

01

2

1

2DC

CHDCH

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

DC BUSOFF

DC BUSOFF

BUSOFF

INVFAULT

BUSOFF

EXT PWR

EMER BATCHG

EMER BUS ESS BUS

STBY BUS

AC BUS 2AC BUS 1

INV 1

DC BUS 1

OFF

ON

OVRD

BAT

MAIN BATCHG

INV 2

DC BUS 2

ON

UTILITYBUS 2

UTILITYBUS 1

DC BUS 1 DC BUS 2

DC EMER BUS

DC STBY BUS

DC ESS BUS

HMBTCHEBTC

SBTC

HBTC

INV 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

BTR

SBTR

115 VAC SBY

26 VAC SBY

115 VAC BUS 2

26 VAC BUS 2

115 VAC BUS 1

26 VAC BUS 1

INV 2

ACBTR

ASTR

#1 INVERTER FAIL SIGNAL

INVERTER FAIL SIGNAL

SDTC

When DC Bus 1 is powered the Static Inverter Override Transfer Contactor (SDTC) closes and the HBTC (Hot Bat Transfer Contactor opens).

FAULTFAULT AVAIL

SHED

SHED

DC GEN 2DC GEN 1

01

2

1

2DC

CHDCH

DC SVCE/UTLY BUS

BAT SEL

MAINEMERG BTC

EXT PWR

EMER BATCHG

EMER BUS ESS BUS

STBY BUS

AC BUS 2AC BUS 1

INV 1

DC BUS 1

OFF

ON

OVRD

BAT

MAIN BATCHG

INV 2

DC BUS 2

ON

UTILITYBUS 2

UTILITYBUS 1

DC BUS 1 DC BUS 2

DC EMER BUS

DC STBY BUS

DC ESS BUS

HMBTCHEBTC

SBTC

HBTC

INV 1

DC SVCEBUS

EXTERNALPOWER

EGHR

GND HDLGBUS

HOT EMERBAT BUS

+ -

HOT MAINBAT BUS

+ -

BTR

SBTR

115 VAC SBY

26 VAC SBY

115 VAC BUS 2

26 VAC BUS 2

115 VAC BUS 1

26 VAC BUS 1

INV 2

ACBTR

ASTR

#1 INVERTER FAIL SIGNAL

INVERTER FAIL SIGNAL

Once the DC Buses are powered, the associated lights are extinguished on the main electrical panel.