The insulators are selected by considering mechanical bending load occurring at that instant of peak short circuit current. During short circuit the insulators supporting the bus-bars experience a bending force and unless these insulators have enough cantilever strength to withstand the dynamic force occurring during short circuits they will fail.
Bolting and clamping should be done by proper grades of steel or of alumimium alloy.
Typical properties for recommended material are
Tensile strength = 71 Kg/Sq. mm.
0.2 % Proof stress (minimum) = 52 Kg/Sq. mm.
Hardness = Brinell 200 minimum Rockwell B 93 minimum
Also absolute minimum contact pressure should be taken as 28 Kg/Sq. cm. and a desirable minimum should be 56 Kg/Sq. cms.
The washers (Plain and spring) should also be used. They should be aluminized or electrogalvanised.
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