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plugged-in GPU is within acceptable parameters. Depressing the EXT
PWR switch when the green AVAIL light is illuminated will close the
GPU anti-flash contactor, connecting the GPU output to the left
generator bus. The ON caption will illuminate and the green AVAIL
caption will extinguish. The GPU may be deselected with the same
switch.
The bus-tie contactor automatically closes when a GPU is connected to
the airplane electrical system. The entire dc system is powered,
assuming the AV MSTR and BATT switches are on and no buses have
been deselected via the electrical control panel.
The airplane generators will not come on line with the GPU selected
ON; and if they are on when the GPU is selected, they will drop off line.
Airplane generators will automatically come on line after engine start,
but not if the GPU is selected ON. The aircraft main batteries do not
have to be on to close the GPU anti-flash contactor; however, only the
bus-tie and non-essential bus contactors will close if neither battery is
selected On. In this case GPU power would only be available to the left
and right generator buses, the left and right non-essential buses, and
the hot buses.
GPU output voltage is indicated on the EICAS/MFD SUMRY page and
on the ELEC system schematic under L/R ESS VOLTS. The EMER BUS
VOLTS will also show GPU voltage. No indication of amps drawn from
the GPU is provided.
The CAS will provide an EXTERNAL POWER message when an
external power cable is connected and EXT PWR will also be
annunciated on the EICAS/MFD ELEC system schematic. These
indications will appear whenever a GPU cable is connected to the
airplane, and a voltage of greater than 5 volts is sensed by the power
monitor. It is not an indication that the GPU meets acceptable
parameters nor does it indicate that the GPU is powering the airplane
electrical system.
Pilot’s Manual
PM-132A 4-9
Operation of the EXT PWR switch on the electrical control panel is also
described under ELECTRICAL SWITCHES in this section.
ELECTRICAL CONTROL PANEL
The dc power system electrical control panel is designed to provide
ease of operation and dark cockpit integration. The automatic load
shedding design for operation with single or dual generator failure
relieves the pilot of manual deselection of electrical buses to prevent an
overload. The control panel reflects and displays batteries, generators,
or buses that have been isolated (automatically shed) in the event of a
fault. The pilot has a manual override option of selecting, recycling or
deselecting some of the buses on the dc system. During engine start, the
generator autostart feature reduces engine start switch selections and
pilot workload.
The electrical control panel consists of an illuminated panel with
thirteen switches. Each switch incorporates lighted captions showing
system status (i.e. OFF/ON). All captions have white letters on a black
background except for AVAIL on the GPU switch, which is green on a
black background. For normal flight conditions, none of the switch captions
should be illuminated.
ELECTRICAL SWITCHES
Following is a description of the switches on the electrical control
panel:
L/R BATT — The battery switches are momentary action switches. If
the aircraft electrical system is powered (one BATT, EXT PWR, or GEN
on), the OFF caption will be illuminated in the L/R BATT switch whenever
the corresponding battery contactor is open. If the battery meets
satisfactory voltage and temperature conditions, the OFF caption will
extinguish when the switch is momentarily depressed and the battery
contactor will close, connecting the battery to the respective generator
bus. The switch will be blank when the battery is on. It will also be dark
(with no OFF annunciations illuminated) when there is no electrical
power applied to the airplane even though the contactor would be
open in this case. The battery contactor will open and the OFF caption
will illuminate if the battery switch is depressed a second time or if the
battery is automatically turned off due to an overheat or an
undervoltage condition.
Pilot’s Manual
4-10 PM-132A
BUS-TIE — Normal automatic operation of this momentary action
switch displays a horizontal bar when the generator buses are tied and
no indication will be illuminated when the buses are split. Automatic
bus-tie operation is described under DISTRIBUTION in this section.
If required, this switch may be depressed to manually override an
automatic bus-tie operation to provide a split system or to tie the
electrical system together. One exception is that it cannot be used to
　
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