Supplementary insulation and reinfo

Supplementary insulation and reinforced insulation shall be so designed or protected that they are not likely to be impaired by deposition of dirt, or by dust resulting from wear of parts within the tool, to such an extent that creepage distances or clearance are reduced below the values specified in 28.1.Ceramic material not tightly sintered and similar materials, and beads alone, shall not be used as supplementary insulation or reinforced insulation.Parts of natural or synthetic rubber used as supplementary insulation shall be resistant to ageing, or be so arranged and dimensioned that creepage distances are not reduced below the values specified in 28.1, even if cracks occur.Insulating material in which heating conductors are embedded serves as basic insulation, and shall not be used as reinforced insulation.Compliance is checked by inspection, by measurement and, for rubber, by the following test:Parts of rubber are aged at a temperature of (100 ± 2) °C for 70 h. After the test, the samples are examined, and shall show no crack visible to the naked eye.NOTE In case of doubt with regard to materials other than rubber, special tests may be made.