MIL-DTL-24640C
4.7.8.3 Procedure. The burner shall be mounted within the chamber, such that the holes in its top are in a
common horizontal plane. The specimen shall be suspended within the enclosure, such that it is parallel to the
burner, horizontally centered directly above the burner, and spaced 1⅞± inches vertically above the top of the
burner surface. Specimen suspension shall be accomplished in a manner (such as by wire loops) which shall not
significantly shield the specimen from flame and which shall prevent any portion of the specimen from dropping
closer than ¾ inch to the top surface of the burner during specimen burning. The gas air supply shall then be
attached to the burner and the gas adjusted to provide a flow rate of not less than that calculated by the following
formula:
Gas flow rate, in cubic feet per hour = 1387 (T+273)/PN
Where:
T
=
Measured ambient temperature in the vicinity of the burner, in °C. Measurement
accuracy shall be within ±0.5 °C.
Local atmospheric pressure, in lb/in2 absolute. Measurement accuracy shall be within ±2
P
=
percent.
Gross heating value, in BTUs/ft3, of the gas at an atmospheric pressure of 14.69 lb/in2
N
=
absolute and a temperature of 23 °C, this value shall be accurate in ±2 percent.
The gas exiting the burner shall then be ignited and the air flow to the burner adjusted to produce the smallest blue
flame possible. The short circuit monitor test voltages shall then be applied to the specimen, as shown in figure 6.
The flame and test voltages shall remain continuously applied to the specimen for a period of not less than that
specified (see 3.1), unless specimen failure (see 4.7.8.4) occurs prior to the end of this period, in which case the test
may be terminated.
4.7.8.4 Observation. Specimen failure shall be construed if any fuse blows or if any overload relay trips prior
to completion of the specified test period (see 3.1).
4.7.9 Heat distortion. This test shall determine the ability of insulation and jacket material to resist physical
deformation when subjected to an elevated temperature.
4.7.9.1 Specimen. Each specimen shall be removed from the completed cable in accordance with (a) and (b),
whichever is indicated. The number of specimens which shall be required shall be in accordance with b(1), b(2), or
b(3), as appropriate.
a. Cable jacket. Each specimen shall consist of a piece of jacketing that has been removed from a finished
cable and a cut to form a rectangular strip. This strip shall be not less than ⅞ inch long nor less than 9/16±1/16 inch
wide, and shall be ground and buffed to a thickness of 0.050+0.010, -0.020 inch with a grinding apparatus (see
4.7.9.2.c). The thickness of the specimen shall be made as uniform as practicable.
Insulation. Each specimen shall consist of a single insulated conductor of length not less than ⅞ inch.
b.
(1) Cables containing four or fewer conductors, one specimen shall be prepared from each insulated
conductor.
(2) Cables containing more than four but fewer than 21 conductors, one specimen shall be prepared from
each of four different insulated conductors (a total of four specimens).
(3) Cables containing 21 or more conductors, the number of specimens prepared shall be equal to the
square root (rounded if necessary, to the nearest whole number) of the total number of conductors. Each specimen
shall be prepared from a different insulated conductor.
4.7.9.2 Special apparatus. Apparatus shall include the following:
28
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business