标准clause 22.21 Wood, cotton, silk, ordinary paper and fibrous or hygroscopic material not used as insulation, unless impregnated. This does not apply to magnesium oxide and mineral ceramic fibres used for the electrical insulation of heating elements.9 e7 k3 v" X& l9 ], z
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Insulating materal is considered to be impregnated if the interstices between the fibres of the material are substantially filled with a suitable insulant.. L, U0 B( S8 O& G( h8 y: \4 A( p) c
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