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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082

provide a glossy finish and to lessen dirt accumula­tion.

(c) Since the loss of a skirt on a pin-type insulator reduces the insulation value of the insula­tor by 30 percent or more, replace such broken units.

b. Nonceramic insulators. Nonceramic or compos­ite insulators include core, weathersheds, and metal-end fittings. A weathershed is the external part of the insulator that protects the core or me­chanical load-bearing component and provides the wet electrical strength and leakage distance. The core consists of resin and glass fibers. The weathersheds are of polymeric materials such as epoxy resins or elastomers and normally contain inorganic fillers.

(1) Construction.

(a) Fiberglass. Fiberglass insulators are manufactured with rods of fiberglass treated with epoxy resins. Rubber-like compounds are applied to the rods to fabricate suspension, dead-end, and post-type insulators.

(b) Polysil. Polysil insulators are formed by using various sizes of silica bound together chemi­cally with a resin into a compound which is approxi­mately 90 percent silica. Insulators have excellent mechanical and dielectric strength, are nontrack-ing, and do not carbonize under severe arcing con­ditions. They are very durable for use in an adverse atmosphere. Polysil was developed by the Electric Power Research Institute (EPRI).

(2) Inspection and replacement.

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