27.2 Electrical connections shall be so designed that contact pressure is not transmitted through
insulating material which is liable to shrink or to distort, unless there is sufficient resiliency in the metallic
parts to compensate for any possible shrinkage or distortion of the insulating material. Ceramic material
is not liable to shrink or to distort.
Compliance is checked by inspection.
27.3 Space-threaded (sheet metal) screws shall not be used for the connection of current-carrying parts,
unless they clamp these parts directly in contact with each other, and are provided with a suitable means
of locking.
Thread-cutting (self-tapping) screws shall not be used for the electrical connection of current-carrying
parts, unless they generate a full-form standard machine screw thread. Such screws shall not, however,
be used if they are likely to be operated by the user or installer, unless the thread is formed by a swageing
action.
Thread-cutting and space-threaded screws may be used to provide earthing continuity, provided that it is
not necessary to disturb the connection in normal use, and that at least two screws are used for each
connection.
Compliance is checked by inspection.
27.4 Screws, which make a mechanical connection between different parts of the tool, shall be secured
against loosening, if they also make electrical connections.
This requirement does not apply to screws in the earthing circuit if at least two screws are used for the
connection, or if an alternative earthing circuit is provided.
Spring washers and the like may provide satisfactory security. Sealing compound which softens on
heating provides satisfactory security only for screw connections not subject to torsion in normal use.
Rivets used for electrical connections shall be secured against loosening if these connections are subject
to torsion in normal use. A non-circular shank or an appropriate notch may be sufficient to comply with
this requirement.
This requirement does not imply that more than one rivet is necessary for providing earthing continuity.
Compliance is checked by inspection and by manual test.
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