21.12 Class I tools shall be so constructed that, should any wire, screw, nut, washer, spring or similar part
become loose or fall out of position, it cannot become so disposed that accessible metal is made live.
Class II tools or class II constructions shall be so constructed that, should any such part become loose or
fall out of position, it cannot become so disposed that creepage distances or clearances over
supplementary insulation or reinforced insulation are reduced to less than 50 % of the values specified in
28.1.
Class II tools or class II constructions, other than those of the all-insulated type, shall be provided with
insulating barriers between accessible metal and motor parts and other live parts.
For class I tools, this requirement can be met by the provision of barriers, or by fixing the parts adequately,
and by providing sufficiently large creepage distances and clearances.
It is not to be expected that two independent parts will become loose or fall out of position at the same
time. For electrical connections, spring washers are not considered to be adequate for preventing the
loosening of the parts.
Wires are considered as likely to become free from terminals or soldered connections, unless they are
held in place near to the terminal or termination, independent of the terminal connection or solder.
Short rigid wires are not regarded as liable to come away from a terminal, if they remain in position when
the terminal screw is loosened.
Compliance is checked by inspection, by measurement and by manual test.
21.13 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.
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