g. Generator Out Warning Annunciators. Two caution/advisory annunciator panel fault annunciators inform
the pilot when either generator is not delivering current to the aircraft DC bus system. These annunciators are
placarded #1 DC GEN and #2 DC GEN . Illumination of the two MASTER CAUTION annunciators and either fault
annunciator indicates that either the identiied generator has failed or voltage is not suficient to keep it connected
to the power distribution system.
The GPU shall be adjusted to regulate at 28 ±.2 volts. the GPU shall be capable of producing 1000
amperes for 5 seconds, 500 amperes for 2 minutes, and 300 amperes continuously.
h. DC External Power Source. See igure 2-44. External DC power can be applied to the aircraft through
an external power receptacle on the underside of the right wing stub, just outboard of the engine nacelle. The
receptacle is installed inside of the wing structure and is accessible through a hinged access panel. DC power is
supplied through the DC external power plug, through the external power relay, directly to the battery bus. Turn off
all external power while connecting the power cable to, or removing it from, the external power supply receptacle.
The holding coil circuit of the relay is energized by the external power source when the BATTERY switch is in the
ON position. the GPU shall be adjusted to regulate at 28 volts maximum to prevent damage to the aircraft battery.
the EXTERNAL POWER annunciator (Fig. 2-42) indicates the DC external power plug is connected. the EXT DC
ON annunciator indicates external power is connected to the aircraft DC bus.
i. Security Key Lock Switch. The aircraft has a security key lock switch (Fig. 2-13) installed on the overhead
control panel, placarded ON OFF. The switch is connected to the battery relay circuit and must be ON when ener-
gizing the battery master power switch. The key cannot be removed from the lock when in the ON position.
j. Circuit Breakers. The overhead circuit breaker panel (Fig. 2-12) contains circuit breakers for most aircraft
systems. The circuit breakers on the panel are grouped into areas which are placarded as to their general function.
A DC power distribution panel is mounted beneath the aisle way, forward of the main spar. This panel contains
higher current rated circuit breakers and is not accessible to the light crew under normal conditions.
2-78. AC POWER SUPPLY.
a. Single Phase AC Power Supply. Inverter units, numbered #1 and #2 (Fig. 2-13) which obtain operational
current from the DC power system, supply AC power for the aircraft. Both inverters are rated at 750 volt-amperes and
provide single-phase output only. Each inverter provides 115 volts, 26 volts, and 400 Hz AC output. The inverters are
protected by circuit breakers mounted on the DC power distribution panel mounted beneath the loor. Controls and
indicators of the AC power system are located on the overhead control panel and in the caution/advisory annunciator
(1) AC Power WARNING/CAUTION Annunciators. Illumination of the two MASTER CAUTION annunci-
ators, and the illumination of caution annunciator #1 INVERTER and/or #2 INVERTER indicates inverter failure.
(2) Instrument AC Annunciator. A red INST AC warning annunciator, will illuminate if all instrument AC
buses should fail.
(3) Inverter Control Switches. Two switches, placarded 1ø INVERTER #1 and #2 on the overhead con-
trol panel (Fig. 2-13), control the single-phase AC inverters.
b. Volt-Frequency Meters. The two digital volt-frequency meters (Fig. 2-13) are mounted on the overhead
control panel to provide continuous monitoring of voltage and frequency on each 115 V AC bus. A reading of 115V
AC and 400 HZ on each meter will indicate normal bus conditions.
c. Three Phase AC Power Supply. Three-phase AC electrical power for operation of the inertial navigation
system and mission avionics is supplied by two, DC powered, 3000 volt-ampere solid state three phase inverters.
(1) Three phase inverter control switches. The two, three-position switches, placarded #1 INV - RESET
- ON - OFF and #2 INV RESET - ON - OFF , located in the mission control panel (Fig. 4-1), control three phase
(2) Three phase volt/frequency meters. Two, digital, three phase volt/frequency meters mounted on
the mission control panel (Fig. 4-1), monitor and display the voltage and frequency outputs of the three phase