SECTION XI. ELECTRICAL POWER SUPPLY AND DISTRIBUTION SYSTEM
The aircraft employs both direct current (DC) and alternating current (AC) electrical power. The DC electrical power
supply (Fig. 2-34) is the basic power system energizing most aircraft circuits. Electrical power is used to start the
engines, power the landing gear and lap motors, and operate the standby fuel pumps, ventilation blower, lights,
and electronic equipment. AC power is obtained from the DC power system through inverters. The single-phase
AC electrical system is shown in igure 2-35, and the three-phase AC electrical system is shown in igure 2-36. The
three sources of DC power consist of one 12-cell/24 volt lead/acid battery and two 400-ampere starter-generators.
DC power may be applied to the aircraft through an external power receptacle on the underside of the right wing
stub, just outboard of the nacelle. Generator control units control the starter-generators. The output of each gener-
ator passes through a cable to the respective generator bus (Fig. 2-34): Other buses distribute power to aircraft DC
loads, deriving power from the generator buses. The generators are paralleled to balance the DC loads between the
two units. When one of the generating systems is not online, and no fault exists, all aircraft DC requirements may
be supplied by either the other on-line generating system or by an external power source. The generator system is
designed to allow cross starting of the other engine. When one generator is on line, all current limiters are bypassed
while starting the other engine. Most DC distribution buses are connected to both generator buses but have isolation
diodes to prevent power crossfeed between the generating systems, when connection between the generator buses
is lost. Thus, when either generator is lost because of a ground fault, the operating generator will supply power for
all aircraft DC loads except those receiving power from the inoperative generator s bus, which cannot be crossfed.
When a generator is not operating, reverse current and over-voltage protection is automatically provided. Two in-
verters operating from DC power produce the required single-phase AC power. Three-phase AC electrical power for
inertial navigation system and mission avionics is supplied by two DC powered three phase mission inverters (Fig.
The mission AC/DC power cabinet (Fig. 2-38) is located on the mission rack, aft of the copilot s seat. AC power
maybe applied through an external power receptacle located in the underside of the left wing stub, just outboard of
the engine nacelle.
2-77. DC POWER SUPPLY.
One lead/acid battery furnishes DC power when the engines are not operating. This 24-volt battery, located in the
right wing center section, is accessible through a panel on the top of the wing. DC power is produced by two engine-
driven 28-volt, 400-ampere starter-generators. Controls and indicators associated with the DC supply system are
located on the overhead control panel (Fig. 2-13) and consist of a single battery switch, two generator switches, two
DC digital voltmeters, and two DC digital load meters.
a. Battery Switch. The switch, placarded BATTERY OFF/RESET - ON (Fig. 2-13), is located on the overhead
control panel under the MASTER SWITCH (gangbar). the BATTERY switch controls DC power to the aircraft bus
system through the battery relay, and must be ON to allow external power to enter aircraft circuits. When the MAS-
TER SWITCH (gangbar) is placed down, the BATTERY switch is forced OFF .
With battery or external power removed from the aircraft electrical system, due to fault, power cannot
be restored to the system until the BATTERY switch is moved to OFF/RESET , then ON .
b. Generator Switches. The two switches (Fig. 2-13), placarded GENERATOR,#1 and #2, are located on the
overhead control panel. The toggle switches control electrical power from the designated generator to paralleling
circuits and the bus distribution system. Switch positions are placarded RESET,ON and OFF.RESET is forward
(spring-loaded back to ON ), ON is center, and OFF is aft. When a generator is removed from the aircraft electrical
system, either due to a fault or from placing the GENERATOR switch in the OFF position, the affected unit cannot
have its output restored to aircraft use until the GENERATOR switch is moved to RESET , then ON .