*
Drive disconnect (2).

These are the alternate-action switches:
*
Battery

*
APU generator

*
Bus tie (2)

*
Generator control (2)

*
Backup generator (2).

The standby power switch is on the P61 overhead maintenance panel. It is a guarded, toggle switch. You use it to manually control standby power.
Battery Switch
The battery switch connects the hot battery bus to the battery bus 2. ON is a mechanical indication that shows the switch is in its latched-in position. OFF is an amber light that shows when the switch is out and the airplane has ac power.
APU Generator Switch
The APU generator switch arms the APU GCU to automatically control APU generator electrical power. ON is a mechanical indication that shows the switch is in its latched-in position. OFF is an amber light that shows when the switch is out. If the APU is on, the light also comes on when the auxiliary power breaker (APB) opens except for when you apply secondary external power to the airplane. The switch is normally in the ON position.
Bus Tie Switches
Each bus tie switch controls the operation of its related BTB. AUTO is a mechanical indication that shows the switch is in its latched-in position. ISLN is an amber light that shows when the switch is out and the BTB is open. The isolation (ISLN) light also comes on if the switch is in AUTO, and the GCU opens the BTB for a fault. The switches are normally in the AUTO position.
External Power Switches
Each external power switch controls the operation of its related external power contactor (EPC). AVAIL is a green light that shows good power quality of the ground power source. ON is a green light that shows a closed EPC. The available (AVAIL) light goes off when the EPC closes.
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ELECTRICAL POWER -OPERATION -GENERAL

Generator Control Switches
Each generator control switch arms its GCU to control IDG electrical power. ON is a mechanical indication that shows the switch is in the latched-in position. OFF is an amber light that shows when the related generator circuit breaker (GCB) is open. The switches are normally in the ON position.
Backup Generator Switches
Each backup generator control switch arms the backup generator converter to control backup electrical power. ON is a mechanical indication that shows the switch is in its latched-in position. OFF is an amber light that comes on for these conditions:
*
Generator control relay (GCR) opens for a fault

*
Engine is shut down

*
Related engine fire switch is pulled out

*
Switch is out.

The switches are normally in the ON position.
Drive Disconnect Switches
The drive disconnect (DISC) switch removes engine gearbox power from the IDG. When you press the switch, the two-piece IDG input shaft moves apart. DRIVE is an amber light that shows that the related IDG has low oil pressure. Plastic guards cover the drive disconnect switches to prevent accidental operation.
Standby Power Switch
The standby power switch has these three positions:
*
OFF

*
AUTO

*
BAT (momentary).

On the ground, the off position makes the static inverter stay off. In the air, the off position has no effect.
The automatic (AUTO) position puts the standby electrical power system under the ELMS control. A guard over the switch moves it to AUTO. The switch is normally in the AUTO position.
To use the battery (BAT) position, you must first push the battery switch to ON. When there is no ac power on the airplane, the switch in BAT turns the static inverter on and makes it supply power to the standby ac bus. When ac power is on, the switch in BAT starts a dc/standby self-test.
Towing Power Switch
The towing power switch lets you supply power only to components that are necessary to safely tow the airplane. When you put the switch in the battery (BAT) position, the towing power light comes on. A guard over the switch moves it to OFF. The switch is normally in the OFF position.
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777 AIRCRAFT MAINTENANCE MANUAL

ELECTRICAL POWER -OPERATION -GENERAL

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ELECTRICAL POWER -INDICATION -INTRODUCTION

General
The EICAS shows electrical power system indications on these formats:
*
Electrical synoptic

*
Electrical maintenance page 1

*
Electrical maintenance page 2.

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