ELECTRICAL - AC

IDG 1 and IDG 2 SELECTOR KNOBS

AUTO: This position closes the IDG contactor, connecting the IDG to the respective AC BUS. When an engine starts, the IDG will automatically come on line, powering the respective AC BUS. The previous power source is disconnected from that AC BUS.

OFF: Opens the IDG contactor, isolating the IDG from the respective AC BUS. IDG is tripped off-line and de-excited.

DISC: Must be held in this position for one second to mechanically disconnect the IDG. After disconnect the flight crew cannot reconnect the IDG.

Source Priority for the AC BUS 1 and 2: Respective IDG (Onside), APU Generator (Inside), Ground Power Unit (Outside), Opposite IDG (Cross-side).

APU GENERATOR BUTTON

PUSH IN: Automatically connects the APU generator to the AC BUS TIE, according to the source priority.

PUSH OUT: Opens the APU generator contactor and isolates the APU generator from the AC BUS TIE.

IDG OIL INDICATOR

• Illuminates for high oil temperature or low oil pressure (HOTLOP) indicating which IDG must be disconnected.

• LED will be OFF after IDG disconnection.

• Associated with an EICAS message.

AC BUS TIES SELECTOR KNOB

TWO OPEN: Opens the Bus Tie Contactor 1, segregating AC BUS 1 from AC BUS 2

AUTO: This position controls the operation of the BTCs, according to system logic. If one of the AC power sources fails, both AC electrical networks are automatically connected by BTCs.

ONE OPEN: Opens the BUS TIE Contactor 2, segregating AC BUS 2 from AC BUS 1.

GROUND POWER UNIT (GPU) BUTTON

PUSH IN: Connects the AC GPU to the AC BUS TIE, according to source priority (AVAIL -> IN USE).

PUSH OUT: Isolates the AC GPU from the AC BUS TIE (IN USE -> AVAIL).

AVAIL: AC GPU is connected and AC power quality requirements (voltage/amperage/frequency) are within limits.

IN USE: AC GPU is powering the airplane.

Before disconnecting the AC GPU the push button must be pushed out. The AC GPU has to be pushed out for the next connection.