S 865-044
(3)
Close these circuit breakers on the main power distribution panel, P6:
(a) 6C7, W/W FIRE DET AC
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747-400 MAINTENANCE MANUAL
E. Wheel Well Detector Loop Continuity and Element Resistance Test
S 865-051
CAUTION: IMPROPER TESTING CAN CAUSE PERMANENT DAMAGE TO THE WHEEL WELL
_______ DETECTOR SYSTEM AND COULD VOID THE MANUFACTURE'S WARRANTY.
DO NOT USE THE INSULATION RESISTANCE "MEGGER" TESTERS OR THE DIELECTRIC VOLTAGE "HYPOT" TESTERS.
DO NOT USE A METER THAT APPLIES DC VOLTAGE EXCEPT WHEN MEASURING THE CENTER CONDUCTOR RESISTANCE.
DO NOT CHECK THE DETECTOR ELEMENTS HEATED TO WITHIN 100 DEGREES F (55 DEGREES C) FO THE ALARM TEMPERATURE SET POINT OF THE DETECTOR.
CAUTION: THE RECEPTACLE (SOCKET) TYPE OF THE END CONNECTORS (FEMALE) CAN
_______ BE DAMAGED BY THE METER LEADS. USE FSS P/N 06-134724-000 OR EQUIVALENT 0.0595 INCH (1.511 MM) TO 0.0615 INCH (1.562 MM) DIAMETER PIN INSERTED INTO THE RECEPTACLE TO PROVIDE A TEST POINT FOR MEASUREMENTS.
(1)
Make sure the the temperature of the detector element is at room temperature (approximately 77 degrees F (25 degrees C).
S 765-046
(2)
Use one of the Tegam meter to measure the resistance between the center pin and the outer sheath of the tube.
S 765-047
(3)
Make sure the minimum allowable insulation resistance is as follows:
(a) 20 Megohm-inches (50 Megohm-cm) for the detector elements with an alarm point of 310 degrees F (154 degrees C).
NOTE: The minimum allowable resistance for an element is found
____ by dividing the constant value shown above by the length of the element (not including the length of the end connectors at each end)
Example, for 22 inches element at 310 degrees F, the mininum allowable resistance is found by dividing 20 Megohms-inches by 20 inches (22 inches minus 2 inches of the length of the connector ends) equal to 1 Megohms.
(b) 100 Megohm-inches (250 Megohm-cm) for the detector element with an alarm point at other temperature than 310 degrees F (154 degrees C).
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(4) S 765-048If the resistance is not between the range shown above, do the continuity test for the wheel well detector elements as follows: (a) Use the mutimeter of one of the Tegam meter to measure the resistance between the ends of the center pin of each element. (b) Make sure the resistance is less than 7 milliohms per inch (2.76 miliohms per cm)
(5) S 865-049Remove the door locks from the wing and body landing gear, if they are not necessary (Ref 32-00-30/201).
(6) S 865-050Remove the ground locks from the wing and body landing gear, if they are not necessary (Ref 32-00-00/201).
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747-400 MAINTENANCE MANUAL
WHEEL WELL OVERHEAT DETECTOR ELEMENT - REMOVAL/INSTALLATION
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