(a)
Put the circuit breaker in its position in the panel.
(b)
Install the nut that attaches the circuit breaker to the panel.
(c)
Tighten the nut.
NOTE: Use a socket wrench to prevent scratches on the panel.
____
(d) If a bus bar was disconnected from the circuit breaker, connect the bus bar: 1) Put the bus bar in its position on the circuit breakers. 2) Install the screws that attach the bus bar to the circuit
breakers.
3) Tighten the screws.
S 434-021
(2) Connect the electrical leads to the circuit breaker:
CAUTION: MAKE SURE YOU CONNECT THE CORRECT ELECTRICAL LEAD TO EACH
_______ STUD ON THE CIRCUIT BREAKER. AN INCORRECT INSTALLATION CAN CAUSE A MALFUNCTION OF THE CIRCUIT AND DAMAGE TO THE EQUIPMENT.
(a) Put the electrical leads in their position on the circuit breaker.
CAUTION: DO NOT INSTALL THE WASHERS BELOW THE ELECTRICAL LEADS.
_______ THIS WILL CAUSE HEAT THAT CAN BURN THE STUDS ON THE CIRCUIT BREAKER.
(b)
Install the screws that attach the electrical leads to the circuit breaker.
(c)
Tighten the screws.
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A 747-400 MAINTENANCE MANUAL
(3) S 414-015Close the access door for the circuit breaker panel.
(4) S 434-016If a lightplate was removed from the P7 panel, install the lightplate: (a) Put the lightplate in its position on the P7 panel. (b) Install the screws that attach the lightplate to the panel. (c) Tighten the screws. (d) Remove the identification tag.
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A
747-400 MAINTENANCE MANUAL
115-VOLT AC POWER DISTRIBUTION - DESCRIPTION AND OPERATION
__________________________________________________________
1. General_______
A. AC power from each airplane source (consisting of the IDGs, the APU generators, and the external power source (when connected)) can be supplied through the main generator feeders, the auxiliary generator feeders, and/or external power feeders to the four main generator load buses.
B. The ground handling bus (GHB) is used for ground operations and can only be powered on the ground. The bus is actually divided into two sections and can be powered by either external power No. 1 or APU generator No. 1. Either power source may be used, but external power No. 1 has priority if both are available. BCU No. 1 controls the application of power to the GHB.
C. Each freighter airplane is equipped with a main deck cargo handling bus and is used for ground operations and can only be powered on the ground. The bus is actually divided into two sections and can be powered by either external power No. 2 or APU generator No. 2. Either power source may be used, but external power No. 2 has priority if both are available. BCU No. 2 controls the application of power to the main deck cargo handling bus.
D. The ground service bus (GSB) is used for both ground and flight operations. The GSB actually consists of two buses called the ground service bus and the ground service utility bus. Any reference to GSB includes both buses unless specifically stated otherwise. The three possible power sources for the GSB are as follows:
(1)
AC bus No. 1
(2)
External power No. 1
(3)
APU generator No. 1
E.
There are eight electrical load control units (ELCUs) used for load distribution. Four are used for control of the galley loads and four for the utility load buses. Each ELCU has internal circuits for control and indication, differential fault, and overcurrent protection.
F.
Two instrument bus voltage sense units (IBVSUs) provide automatic transfer of the captain's and first officer's flight instrument transfer buses. The IBVSUs transfer the associated flight instrument transfer buses from their primary source to ac bus No. 1 if the primary source voltage drops below 97 volts.
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