Electrics - External Power Show Schematic only

DC Electrical System Airplanes with 90-minute standby power - The main and APU batteries are paralleled if power is lost at the left 28 volt DC bus. APU Battery main Battery Battery Switch Battery Discharge Lights Static Inverter Standby Power Selector Switch Standby Power OFF Light Hot Battery Buss Battery Bus Standby DC Bus Standby AC Bus Left Main DC Bus Right Main DC Bus Centre Buses As Installed Power will transfer providing at least 2 generators are operating and 3 autopilots armed for approach If there is a loss of power on one of the two DC buses, the DC BTB will close automatically. AC Electrical System Start APU Select External Power OFF Start Left Engine Start Right Engine AC Buses and Load Shed System Generator Drive Disconnect Generator Drive Disconnect AC Bus Tie System AC Bus Tie System Generator Control Switch Generator Control Switch Ground Service Switch Ground Service Bus Ground Handling Bus - The Ground Handling Bus can only be powered on the ground by the APU or External Power. It cannot be powered from the engine-driven generators Left AC Bus OFF Light Right AC Bus OFF Light Left Flight Instrument Transfer Relay Right Flight Instrument Transfer Relay Left AC Bus Right AC Bus Captain's Flight Instruments Transfer Bus First Officer's Flight Instruments Transfer Bus

External power must be manually selected. Pushing the External Power Switch replaces the engine generator or APU power with external power. If the external power is powering the buses and an engine is started, that engine automatically powers its respective bus. External power is also removed from the buses by pushing the External Power Switch as second time.