Embraer EMB145 Operation Manual page 1706

AIRPLANE ELECTRICAL
OPERATIONS
MANUAL
EXTERNAL POWER SOURCE
The Ground Power Unit (GPU) is connected to the airplane through an
external receptacle. The GPU supplies 28 V DC to the load buses for
ground operation and APU starting, independently of the internal
batteries.
The GPU has priority over any battery and generator when energizing
the airplane. Thus, the generators and the batteries cannot operate in
parallel with the GPU.
The GPU Button, located on the overhead panel, controls the External
power supply. As soon as the Ground Power Unit is energized,
properly connected to the airplane receptacle, ready to supply power
but not connected to the buses, the GPU AVAIL inscription illuminates
on the GPU Button. An identical inscription above the GPU receptacle
simultaneously illuminates.
When GPU AVAIL is illuminated and the batteries are not connected
to the buses, only the GROUND SERVICE BUS is supplied through
the external power supply. When the GPU Button is pressed, the
Ground Power Contactor (GPC) will close, allowing the external power
to feed the load buses. When the external power comes on line, the
GPU AVAIL inscription on the GPU Button extinguishes itself and the
white stripe on the button lower half illuminates.
An overvoltage circuit isolates the GPU from the airplane's electrical
buses if the GPU voltage is incorrect. External power inverse polarity
protection is also provided. To reset the system, release the GPU
button and then press it again. If the GPU overvoltage persists, GPC
will be kept open.
The external power voltage can be monitored through the electrical
page, on the MFD. The electrical system page shows the GPU box
and its voltage. The GPU voltage indication is removed in flight.
Page Code
2-05-05 5 01
REVISION 36