2.  Operation

A.  The airplane may be connected to 3-phase, 400-Hz, 115-volt external power with or without engine generators running. When the plug is inserted into the external power receptacle (Fig. 2), the GROUND POWER AVAILABLE light comes on near the ground power (GND PWR) switch on the overhead panel (P5.) The external power connected light at the external power receptacle also comes on. A jumper in the ground power plug connects pin F to E at the receptacle, so that the dc now supplied by the ground power T-R unit is available for all control purposes and for energizing both 28-volt dc external power buses. The external power NOT IN USE light at the receptacle will be ON. When the GND PWR switch (S1) is moved to ON, the NOT IS USE light goes out and the external power CONNECTED light, at the receptacle, remains on. Just before the EXT PWR contractor closes there is a short time delay while the generator breakers open, clearing any airplane generators from the tie bus. With the No. 1, 2 and the APU generator lines all open, the external power contactor R8 closes. Loads previously carried by airplane generators are now supplied from the ground source. The above sequence will take place whether or not there is a storage battery connected in the airplane or whether or not any generators are running when the external power plug is inserted.
B.  When changing from ground power to engine-driven generator power it is recommended that the selector knob on the overhead panel be turned to the appropriate generator as that engine is started. Then the BUS TRANSFER switch should be moved to AUTO and the GEN switch on the monitored generator should be moved to ON, when the generator is up to speed, the low oil pressure light on the CSD indicator panel will go out. When frequency is approximately 400 Hz, and the voltage indicated is about 115 volts for this particular generator the external power contactor will drop out automatically., and the NOT IN USE light will come on, indicating to the ground crew that the plug may be pulled out of the receptacle. Arcing and considerable damage to the external power receptacle pins may result from pulling the plug before the NOT IN USE light is illuminated. The CONNECTED light goes off when the external power plug is pulled or if circuit breaker C812 is opened. The ground service relay R6, the refueling power control relay R11 and the external power contactor R8 must all be relaxed for the external power NOT IN USE light to be ON (Fig. 1). The jumper mentioned above must complete the circuit from pin E to F to light the entry lights. The DC supply to ground support equipment, such as ground fueling, is obtained from the pin E side of the circuit.
C.  The battery may be charged from a 3-phase, 115-volt, 400-Hz ground power source (Fig. 1). An APU start interlock relay R39 is in the battery charger input circuit to protect the charger while operating the APU start motor from the airplane battery.
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24-41-0 Page 4  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Nov 1/74 

EXTERNAL POWER RECEPTACLE - REMOVAL/INSTALLATION
1.  General

A.  This procedure has two tasks. One task is the removal of the external power receptacle. The other task is the installation of the external power receptacle.
B.  The external power receptacle is on the lower right side of the airplane. It is installed forward of the wheel well for the nose gear.
C.  The external power receptacle is part of the pressure seal of the airplane. You must seal the receptacle after you install it.
2.  External Power Receptacle Removal (Fig. 401)
A.  References

(1)  24-22-0/201, Manual Control
B.  Access

(1) 
 Location Zone
202 Lower Nose Compartment

(2) 
 Access Panel
1101 External Power Receptacle Door

C.  Procedure

(1)  
Make sure all electrical power is off (Ref 24-22-0/201).

(2)  
Disconnect all electrical power cables from the external power receptacles.

(3)  
Open the door 1101 for the external power receptacle, if it is closed.

(4)  
Open the forward panel on the right side of the nose wheel well to get access to the receptacle.

(5)  
Disconnect the electrical leads from the receptacle:

(a)  
Remove the three nuts that attach the conductor guard to the bracket.

(b)  
Remove the three bolts that attach the conductor guard to the receptacle pan.

(c)  
Remove the conductor guard.

(d)  
Attach an identification tag to each lead.

(e)  
Remove the nuts and washers that attach the six leads to the receptacle studs.

(f)  
Disconnect the leads from the studs.

 
　
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