(2) AC Control Circuit. The 115 V ac, three-phase input is applied to the power distribution box at
connector pins J1-C, J1-D, and J1-E. AC neutral and ground are provided at connector pins J1-F and J1-G.
The phase-one ac input passes to FANS circuit breaker CB6 when MISSION POWER switch S1 is set to ON
and the relay K2 contacts close. When FANS circuit breaker CB6 is set to on (in), all three phases pass
through terminal board TB3 and connector J2 to external LRUs in the system. The phase-one input through
terminal board connection TB3-3 also operates relay K1 in the dc power distribution circuit and relay K4. When
relay K4 operates, contacts A2 and A3 open to remove the ground from filter FL6 in the RFI filter assembly.
(3) Interlock Jumpers. The interlock circuit originates at the ac neutral line. The neutral potential is
routed through the power distribution box and through external equipments in the system. The power
distribution box interlock circuit consists of jumpers between connector pins J2-W and J2-R, J2-P and J2-J, J2-
BB and J2-FF, J2-u and J2-AA, J2-t and J2-m, J2-k and J2-e, and J2-X and J2-d. When all of the external
units are installed and connected, the ac neutral potential passes through connector pin J2-MM to the coil of
relays K1 and K4. If any unit is removed or disconnected, the interlock circuit is opened and relays K1 and K4
b. DC Power Distribution Circuit. The dc power distribution circuit provides individual paths through
circuit breakers CB9 through CB20. As shown in figure 3-2, each circuit breaker protects a +28 V dc circuit to
external units in the system or to filters FL1 through FL5 in the RFI filter assembly. Table 3-1 lists the panel
marking and rating for each circuit breaker in the dc power distribution circuit. The following paragraphs
describe the distribution paths protected by circuit breakers CB12 and CB20.
(1) Circuit Breaker CB12 Distribution. When PP-7294A circuit breaker CB20 is set to on (in), the +28 V
dc power passes through connector pin J5-M to external equipment in the system.
(2) Circuit Breaker CB20 Distribution. When KG-45 circuit breaker CB20 is set to on (in), the +28 V dc
power passes through connector pin J5-M to external equipment in the system.
c. AC Power Distribution Circuit. The ac power distribution circuit provides individual paths through
circuit breakers CB1 through CB8. As shown in figure 3-3, each circuit breaker protects a 115 V ac circuit to
external equipment in the system. Table 3-2 lists the voltage phase, panel marking, and rating of each circuit
breaker. The following paragraphs describe the distribution paths protected by circuit breakers CB1 and CB2.