MIL-DTL-917F(SH)
TABLE VIII. Molding compounds (thermoplastic material).
Applicable
Compounds
Type
Max. temperature, °F (°C)
document
Polyamide (nylon)
Type III, Grade E
ASTM D6779
221 (105)
Polycarbonate
----
ASTM D3935
221 (105)
3.4.1.4 Ceramics. Ceramics may be used only where they constitute integral portions of specified parts.
3.4.1.5 Silicone. The use of silicone shall be as specified in 3.3.1.4.
3.4.2 Insulating material. Detailed discussion of electrical insulation and temperature limits is contained in
IEEE 1.
3.4.2.1 Classes and definitions of insulating materials. Temperature classes of insulating materials have
traditionally been established by definition based on a chemical composition of the materials. Methods of
temperature classification based on the results of thermal evaluation tests are coming into use as specified (see 6.2).
Since the temperature classification of a material that has been accepted for a long time will have been established
by field experience, its life-temperature characteristics determined by test provide a basis for comparison with the
thermal life of a new material. The purpose of assigning each material to a definite temperature class, therefore, is
to facilitate comparisons between materials and to provide a single number to designate each class for purposes of
standardization. The life expectancy under the test conditions may be shorter than, and has no direct relation to, the
life expectancy of the material in actual service. Materials or combinations of materials other than those listed in
table IX may be included in a given class if, by experience or accepted tests, they can be shown to have comparable
thermal life at the associated temperature index.
3.4.2.2 Accepted tests. The words "accepted tests" in paragraph 3.4.2.1 above are intended to refer to
recognized industry or military test procedures established for the thermal evaluation of materials by themselves or
in simple combinations. Experience or test data used in classifying insulating materials are distinct from the
experience or test data derived for the use of materials in complete insulation systems. The thermal endurance of
complete systems may be determined by test procedures specified elsewhere in this specification or in related
equipment specifications. A material that is classified as suitable for a given temperature may be found suitable for
a different temperature, either higher or lower, by insulation system test procedures. For example, it has been found
that some materials suitable for operation at one temperature in air may be suitable for a higher temperature when
used in a system operated in an inert gas atmosphere. It is important to recognize that other characteristics, in
addition to thermal endurance, such as mechanical strength, moisture resistance, and corona endurance, are required
in varying degrees in different applications for the successful use of insulating materials.
3.4.3 Insulation systems.
3.4.3.1 Temperature classification of insulation systems. Materials of a given temperature index may be used
as parts of complete insulation systems that are assigned widely different temperatures, depending on the results of
thermal tests of the insulation system. The insulation system classification specified in table IX shall be used for
Navy equipment and shall be specified in the individual equipment specification (see 6.2). The materials used in
electrical systems shall be characterized by the specific limiting temperatures at the temperature indices shown in
table IX. These temperatures are based on service experience or on accelerated life test data that demonstrates an
equivalent life expectancy. New or modified systems shall be evaluated by acceptance test procedures and, when so
evaluated, shall have equal or longer thermal endurance than a service-proven system of the class at the test
conditions. A new insulation system may also be classified in a higher class by test if it has equal or greater thermal
endurance at higher test temperatures when compared to a service proven insulation system under the same test
conditions.
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