Cessna 208B - Generator or Main Bus Malfunctions

CESSNA
SECTION
3
MODEL 208B (675 SHP) EMERGENCYPROCEDURES
ELECTRICAL POWER SUPPLY SYSTEM
MALFUNCTIONS
(Continued)
GENERATOR OR MAIN BUS MALFUNCTIONS
Illumination of the VOLTAGE LOW annunciator is a warning that the
power distribution bus voltage is low enough to start discharging the
battery. The
volt/ammeter (in VOLTS position) is used to verify the low
bus voltage. A low or zero reading of the
volt/ammeter (in GEN
position) confirms that the charge is insufficient or generator output
current is zero. If the GENERATOR OFF annunciator is illuminated, it
indicates that the generator contactor has disconnected the generator
from the power distribution bus. The most likely causes of a generator
trip (disconnection) are line surges, tripped circuit breakers or
accidental switch operation. In these cases, follow the checklist
procedures to restore generator operation.
The airplane is equipped with two starter contactors. One is used for
starts on external power and the other for battery starts. If either
contactor does not open after reaching approximately 46% N the
amber STARTER
ENGERGIZED annunciator will remain illuminagd. In
most cases when this occurs, the generator will not transfer to the
generator mode, and the GENERATOR OFF annunciator will remain
illuminated. Under these conditions, it will be necessary to shut down
the engine using checklist procedures and correct the malfunction prior
to flight.
The electrical power distribution system consists of a primary power
distribution bus in the engine compartment which receives power from
the battery and the generator, and two (No.
1 and No.2) main power
buses located in the circuit breaker panel. The main buses are each
connected to the power distribution bus by three feeder cables. Each
feeder cable is protected by a fuse link and a circuit breaker. This
multiple feeder system provides automatic isolation of a feeder cable
ground fault. If one of the three 30-amp feeder circuit breakers on either
bus opens, it should be assumed that a feeder cable ground fault has
been isolated, and attempted resetting of these breakers prior to
troubleshooting is not recommended. The electrical load on the
affected bus should be maintained below the remaining 60-ampere
capacity.
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U.S.
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