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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
SEE A SEE B
EXTERNAL
POWER EXTERNAL
CONTACTOR 1 POWER
SEE C GROUND POWER CONTACTOR 2
CURRENT SEE C
TRANSFORMER
NO. 2
SEE D
GROUND POWER
CURRENT
TRANSFORMER
NO. 1
P714 AUX/EXT SEE D P715 AUX/EXT
NO. 1 POWER CENTER NO. 2 POWER CENTER
A B
GROUND POWER CURRENT TRANSFORMER (TYPICAL) EXTERNAL POWER D
CONTACTOR (TYPICAL)
C
NOTE: TERMINAL LEADS NOTSHOWN FOR CLARITY.
External Power Contactor/Ground Power
Current Transformer Location
Figure 2
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
SEE A
SEE B
A
BULKHEAD
EXTERNAL POWER TRANSFORMER RECTIFIER UNIT A
TERMINAL
BLOCK COVER
EXTERNAL POWER TRANSFORMER RECTIFIER UNIT B
FWD
TERMINAL BLOCK COVER
B
External Power Transformer Rectifier Unit Location Figure 3
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24-41-00
ALL ú ú 01 Page 5 ú Feb 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
7. Operation
_________
A. Functional Description
(1)
External power, rated at 115 volts ac 3-phase 400 Hz, is supplied to the airplane through two external power receptacles.
(2)
Both of the external power receptacles are connected to the airplane sync bus through the external power contactors (XPCs) using AWG 1/0 copper conductor three-phase feeders, supplying power to the main load buses via the BTBs and SSB.
(3)
Pins A, B, and C in the external power receptacle are used to conduct the three-phase electrical power.
(4)
Pins E and F in the external power receptacle are use by the BCUs to check for proper seating of the external power plugs. If the external power plug is not fully seated, the E/F interlock circuit in the corresponding BCU will inhibit application of external power to the airplane (the AC CONNECTED light on the P36 and the AVAIL light on the P5 will not illuminate). For the E/F interlock circuit, the BCU supplies 28 volts dc to pin F and senses 28 volts dc at pin E. The two most common configurations used for completing the E/F circuit are as follows:
(a)
Pin F is shorted to pin E when the external power plug is connected. In addition, many ground power units sense the 28 volts dc at pin F to control application of the 3-phase power.
(b)
Pin F supplies 28 volts dc to the hold-in coil of a manually set ground contactor. Closing of the contactor energizes pin E at 28 volts dc and connects 3-phase power to the plug.
(5)
The BCU E/F interlock circuit also detects shorts to ground or to the main feeder wires. When the E/F interlock protection is activated due to a short, the BCU will inhibit application of external power to the airplane (the AC CONNECTED light on the P36 and the AVAIL light on the P5 will not illuminate). Once activated, the E/F interlock protection circuit in the BCU is latched and must be reset by one of the methods as follow:
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