Code of Practice for the Electricity (Wiring) Regulations - 2009 Edition

(d ) An earthing terminal should be provided and be so arranged that the
earth wire of the cable, if any, is visible at least when the plug or
appliance inlet is removed from the corresponding socket outlet or
connector.
(5) Screws and connections
(a) Screwed connections, electrical and otherwise should withstand the
mechanical stresses occurring in normal use. Screws transmitting
electrical contact pressure should screw into metal.
(b) Screws should not be made of insulating material if their replacement by
a metal screw would affect the safety or performance requirements of
the accessory.
(c) Where current carrying parts are screwed together, the current path
should not rely on the screw threads.
(6) Creepage distances, clearances and distances through
insulation
(a) When the socket outlet is correctly assembled and wired with the
appropriate cable, the minimum clearance through air and the minimum
creepage distance shall be 2.5 mm:
(i) between live parts of opposite polarity;
(ii) between live parts and any other metal parts; and
(iii) between live parts and the accessible external surface of the
accessory.
(b) The socket outlet should have a minimum distance of 2 mm between
insulated live parts and the accessible external surface.
(7) Accessibility of live parts
Socket outlets should be so designed that when mounted and wired as in
normal use, live parts are not accessible as tested by a test finger shown in
Figure A3(6).
(8) Provision of earthing
(a) Socket outlets should be so constructed with scraping earthing contact
that, when inserting the plug, the earth connection is made before the
current carrying pins of the plug become live. When withdrawing the
plug, the current carrying parts should separate before the earth contact
is broken.
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