# ELECTRICAL - DC

![](//cdn.document360.io/417c2d4d-fdb8-4d4d-b11d-011fe445d776/Images/Documentation/electrical-panel--dc-image-6iw5x5rl.png)

### TRU 1 and TRU 2 TOGGLE <a href="#toc118376396" id="toc118376396"></a>

**AUTO:** Automatic operation of the electrical system. Connects TRU 1 (2) to the respective DC bus

**OFF:** Isolates TRU 1(2) from the respective DC bus

### TRU ESS SWITCH <a href="#toc118376397" id="toc118376397"></a>

**AUTO:** Automatic operation of the electrical system. Connects TRU ESS to the ESS BUS 3

**OFF:** TRU ESS is isolated from ESS BUS 3

NOTE: DC GPU supplies power to only APU START BUS. It does not charge the batteries.

![](//cdn.document360.io/417c2d4d-fdb8-4d4d-b11d-011fe445d776/Images/Documentation/electrical-panel--dc-image-71zv7mwa.png)

### BATT 1 SELECTOR KNOB <a href="#toc118376398" id="toc118376398"></a>

**ON:** Connects Battery 1 to DC ESS BUS 1

**OFF:** Power is only supplied to HOT BATT BUS 1

**HOT BATT BUS 1 powers:** Engine 1A and 2A fire extinguisher, engine fuel shutoff valve 1, hydraulic system shutoff valve 1, engine 1 oil level indication, Courtesy/Service lights fwd, DC ceiling lights.

### BATT 2 SELECTOR KNOB <a href="#toc118376399" id="toc118376399"></a>

**AUTO:** Connects Battery 2 to DC ESS BUS 2. Allows Battery 2 to power the APU START BUS during APU start.

**OFF:** Power is only supplied to the HOT BATT BUS 2

**HOT BATT BUS 2 powers:** Engine 1B and 2B fire extinguisher, engine fuel shutoff valve 2, hydraulic system shutoff valve 2, engine 2 oil level indication, refueling panel, Water and Waste controller, and CMC.

NOTES:

* Supply essential loads for 10 minutes.
* On ground if powered only by batteries for more than 5 minutes a horn will sound.
* Wait to turn the batteries off when leaving the aircraft until the APU off and APU FUEL SOV CLSD EICAS messages are displayed (approx.. 80 seconds).

### DC BUS TIES <a href="#toc118376400" id="toc118376400"></a>

**AUTO:** Allows automatic operation of the electrical system.

**OFF:** DC bus ties open.


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