Cessna 402C - Page 229

SECTION 7
AIRPLANE & SYSTEMS DESCRIPTIONS
EMERGENCY POWER ALTERNATOR FIELD SWITCH
An emergency power alternator field switch, see Figure 7-18, is located
on the aft top side of the side console. The switch is used when the
alternators will nof sel f-excite. Placing the switch in the ON position
provides excitation from the battery even though the battery is considered
to have failed.
OVERVOLTAGE RELAYS
Two overvoltage relays in the electrical system constantly monitor their
respective alternator output. Should an alternator exceed the nonnal
operating voltage, the overvoltage relay will trip, taking the affected
alternator off the line. The overvoltage relay can be reset by cycling the
applicable alternator switch.
VOLTAMMETER
A voltammeter, see Figure 7-18, located on the left side console, is
provided to monitor alternator current output, battery charge or discharge
rate and bus voltage. A selector switch, see Figure 7-18, labeled L ALT, R
ALT, BATT, and VOLTS is located to the left of the voltammeter. By posi-
tioning the switch to L ALT, R ALT, or BATT position, the respective alter-
nator or battery amperage can be monitored. By positioning the swi tch to
the VOLTS position, the electrical system bus voltage can be monitored.
CIRCUIT BREAKERS AND SWITCH BREAKERS
All electrical systems in the airplane are protected by push-to-reset
type circuit breakers or switch breakers, see Figure 7-18. Should an
overload occur
in any circuit, the resulting heat rise will cause the
controlling circuit breaker to "pop" out, opening the circuit or allowing
the switch breaker to return to the OFF position. After allowing to cool
for approximately three minutes, the circuit breaker may be pushed in
(until a cl ick is heard or felt) or the switch breaker may be returned to
the ON position to reenergize the circuit. However, the circuit breaker
should not be hel d in nor the switch breaker forced to remain in the ON
position if it opens the circuit a second time as this indicates a short
ci rcult.
EXTERNAL POWER RECEPTACLE
An optional external power receptacle may be installed in the left wing
aft nacelle fai ri ng. The receptac 1e accepts a standard AN-type external
.............- power source plug. The following precautions must be observed when start-
ing an airplane using an external power source:
1. Avionics Master Switch -
OFF.
2. Battery Switch - ON (The battery will tend to absorb transients
that are present in some external power sources).
3. Alternator Switches - OFF.
4. Airplane Voltammeter - READ battery voltage.
-
.---------NOTE--------,
Set External Power Source Output Voltage to 28 volts.
5. External Power Sour~e - TURN OFF before connecting to airplane.
6. External Power Source - ATTACH and TURN ON.
1 November 1979
Revision 4 - 1 December 1983
7-251