MIL-DTL-917F(SH)
3.3.3 Plastics. Plastics which serve as electrical insulation shall be in accordance with 3.4.1. Plastics which do
not serve as electrical insulation (structural parts and so forth) shall meet all physical and mechanical properties
required for plastic insulating materials, including non-flammability and non-toxicity; however, these plastics need
not meet the arcing and tracking resistance requirements. Unless otherwise specified (see 6.2), the color of plastics
shall be as follows:
a.
b. Exterior plastic materials that are not painted shall match the color of MIL-DTL-15090 enamel, except
where transparency is required.
c.
Internal plastic materials which do not serve as electrical insulation shall be any color.
3.3.3.1 Dials and other transparent and translucent applications. Plastic for dials and other transparent and
translucent applications shall be in accordance with MIL-W-80. Material conforming to MIL-PRF-5425 may be
used, provided it is treated with an anti-electrostatic coating. Commercial grade polycarbonate or equivalent may be
used where mechanical considerations are of primary importance, and transparency importance is secondary.
3.3.4 Glass. Glass for protection of indicator dials and for viewing windows shall meet requirements and be of
the shatterproof type in accordance with Class 1, Type I, of ANSI/SAE Z26.1 and SAE J673 (see 3.3.1.10). Glass,
so applied, shall be clear and present no evidence of distortion of the viewed object when viewed at any angle.
Design and application shall be so that conditions configurative to condensation of moisture on the glass are
avoided. Glass windows for meters which are not internally illuminated shall be glareproof.
3.3.5 Recycled, recovered, environmentally preferable, or biobased materials. Recycled, recovered,
environmentally preferable, or biobased materials should be used to the maximum extent possible, provided that the
material meets or exceeds the operational and maintenance requirements, and promotes economically advantageous
life cycle costs.
3.3.6 Non-preferred component materials. The following component materials are non-preferred, but allowed,
and shall be identified as specified (see 6.2) prior to the start of first article testing:
a. Insulating materials which contain halogens, e.g., chlorine, fluorine, and bromine, which evolve gases
during combustion, including estimated maximum weight.
b. Organic materials not inherently fungus-resistant or validated to be fungus-resistant. Refer to
MIL-HDBK-454, Guideline 4.
c.
Corrosion-susceptible materials not in accordance with 3.3.2.3.
d.
Lead free solder used for printed circuit boards.
e.
Type 1 compositions containing hexavalent chromium in accordance with MIL-DTL-5541.
3.4.1 Insulation materials.
3.4.1.1 Arc and tracking resistance. Structural insulators, such as laminates, molding compounds,
encapsulating materials, bus bar coverings, and similar materials subject to arcing conditions shall have an arc
resistance of not less than 130 seconds and a track resistance of not less than 70 minutes (see 4.4.2.3). This applies
to low voltage (under 2,000 V) equipment. For equipment rated at 2,000 V or higher, an arc resistance of
150 seconds and a minimum track resistance of 300 minutes shall be required.
3.4.1.2 Laminated plastics. Laminated plastics in the form of sheets, rods, or tubes shall be used where rigid
materials with dielectric properties are needed. Such laminates shall meet the temperature, mechanical, and
electrical requirements of each application. Other forms, such as channels and formed shapes, except spacers, shall
be used only when approved for the particular application (see 3.3). For spacers, see 3.4.9. Laminates shall meet
the minimum requirements for toxicity (see 3.3.1.1), flame resistance (see 3.3.1.9), and arc and tracking resistance
(see 3.4.1.1).
3.4.1.2.1 Machined edges. Machined edges on glass based laminates shall be sealed with an appropriate
coating to prevent moisture infusion.
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