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tenance
work
on
the
airplane
electrical
system
(with
the
exception
of elec-
tronic
equipment).
NOTE
Electrical
power
for
the
airplane
electrical
circuits
is pro-
vided
through
a split
bus bar
having
all electronic
circuits
on one side
of
the
bus and other
electrical
circuits
on
the
other
side
of
the
bus.
When
an
external
power
source
is
connected,
a contactor
automatically
opens
the
circuit
to
the
electronic
portion
of
the
split
bus
bar
as a protection
against
damage
to the transistors
in
the
electronic
equip-
ment
by
transient
voltages
from
the
power
source.
There-
fore,
the
external
power
source
can not be used
as a
source
of power
when checking
electronic
components.
Just before
connecting
an external
power
source
(generator
type
or bat-
tery
cart),
the
master
switch
should
be
turned
ON.
The ground
service
plug receptacle
circuit
incorporates
a polarity
re-
versal
protection.
Power
from
the
external
power
source
will flow only if
the
ground
service
plug is correctly
connected
to the
airplane.
If
the
plug
is accidentally
connected
backwards,
no power
will flow
to the
airplane's
electrical
system,
thereby
preventing
any damage
to
electrical
equipment.
The battery
and external
power
circuits
have been designed
to
com-
pletely
eliminate
the
need
to
"jumper"
across
the
battery
contactor
to
close
it for charging
a completely
"dead"
battery.
A
special
fused
circuit
in
the
external
power
system
supplies
the
needed
"jumper"
across
the
contacts
so
that
with a "dead"
battery
and an external
power
source
applied,
turning
the
master
switch
ON will close
the
battery
contactor.
STATIC PRESSURE ALTERNATE SOURCE
VALVE.
A
static
pressure
alternate
source
valve
is available
to
provide
con-
tinued
operation
of
the
airspeed
indicator,
altimeter
and vertical
speed
indicator
in
the
event
that the
static
system
ports
or lines
become
ob.
structed.
If erroneous
instrument
readings
are
suspected
due
to
water
or ice
in
the
static system
ports
or lines,
the
static
pressure
alternate
source
valve
knob should
be pul1ëd on, venting
the
static system
to the
cabin.
7-2
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