(e)  
P415, Right Power Distribution Center 1) 415H32, F-O PWR SEAT

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747-400 MAINTENANCE MANUAL
 WATER LINE AND WASTE DRAIN HEATERS - DESCRIPTION AND OPERATION
______________________________________________________________
General (Fig. 1)
_______
 A.  Electric heaters prevent the formation of ice in the water supply lines, waste water drain lines, drain masts, and waste tank service fittings in the unheated areas of the airplane. The heater types used are: integrally heated water supply hoses, inline water supply line heaters, ribbon heaters which are wrapped around drain lines, integrally heated drain masts, blanket heaters, and a drain gasket heater and heated flush fittings for the toilet drain servicing assembly.
 B.  When airplane electrical power is on, 115 volts ac is supplied to the water and drain heaters. Thermostats are provided in heater circuits where excessive heating is undesirable. The drain cap gasket heater has a low wattage output and continuous operation will not cause overheating. When the airplane is in the air, the drain mast heaters are supplied with 115 volts ac. On the ground, the ground safety relay transfers the drain mast heaters to 42.5 volts ac (Fig. 2).
Water Supply Line Heaters
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 A.  The potable waterlines distribute water from water storage tanks in the aft bulkhead of the forward cargo compartment to the galleys and lavatories. Potable water supply lines are kept free of ice by inline heaters and integrally heated hoses.
Waste Water Heaters
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 A.  The waste water system gathers waste water from the washbasins and galley drains and dumps it overboard through the drain masts. There are three waste water drain systems, each terminating in a heated drain mast.
 B.  The waste water drain lines to the drain masts are heated where they pass through the unheated section of the airplane. The 115-volt ac ground handling bus supplies power to these heaters at all times. Drain line heaters are the ribbon type and are controlled by thermostats. Some ribbon heaters have built-in thermostats.
 C.  The drain mast is electrically heated to prevent ice formation. The heating elements to the drain mast are integral to the mast (AMM 38-31-00/001).
 D.  The drain mast heaters do not have a thermostat. However, the power to the drain mast heaters is reduced from 115 volts ac in the air to 42.5 volts ac when the airplane is on the ground.
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A
747-400
MAINTENANCE MANUAL

FWD  HEATER GASKET  RINSE FITTING HEATER 
SEE  A 
SEE  B 
HEATER RIBBON  WASTE TANK SERVICE PANEL A 
FWD 
MAST DRAIN HEATED 
B 

HEATER
ELEMENT
CONTROLLER

HEATED SUPPLY HOSE (EXAMPLE)
IN-LINE HEATER (EXAMPLE)
Water Line and Waste Drain Heaters - Component Location
Figure 1 (Sheet 1)

D19970
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

UPPER DECK LAVATORY
UPPER DECK GALLEY
WATER TANK (EXAMPLE)
WATER TANKS
WATER
SEE C

SERVICE
PANEL
ELECTRICALELECTRICAL CONNECTOR CONNECTOR FOR THE FOR THE IMMERSION THERMOSTAT HEATER (EXAMPLE) (EXAMPLE)
D
WATER TANKS
SEE D
SUPPLY TO GALLEY AND LAVATORY
SERVICE PANEL
C
Water Line and Waste Drain Heaters - Component Location
　
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