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

(5) Transformers
(a) Every transformer should be double wound with windings insulated
with material to a minimum quality of class E insulation and
tropicalised.
(b) One point of the secondary winding of every transformer should be
connected to an earthing terminal on the body of the container.
(c) The secondary voltage of every transformer should not exceed 5 kV
r.m.s. to earth on open circuit.
(d ) Every high voltage circuit supplied from a transformer having a rated
input exceeding 500 watts should be provided with means for
automatic disconnection of the supply at the supply end of the
transformer in the event of a fault current exceeding 20 percent of
the normal steady current in the circuit.
(e) The rating plate of every transformer should carry:
(i) the maker’s name,
(ii) open-circuit secondary voltage,
(iii) rated secondary current,
(iv) rated primary voltage, and
(v) rated primary current.
(6) Barrier for live parts
(a) All live parts, including all conductors but excluding the tubes except
in the neighbourhood of their terminals, should be provided with
effective barriers of earthed metal or insulating materials, or
mechanical strength adequate to withstand the conditions of normal
service, or alternatively, for installations on the exterior of a building,
such live parts may be so situated as to be accessible only to
responsible persons.
(b) Barriers made of insulating material used for this purpose should be
non-hygroscopic, anti-tracking and substantially non-ignitable. Glass
barriers may be used only if so situated as to be accessible only to
responsible persons.
(7) Earthing
Exposed conductive parts and metalwork inclusive of metal frames of
high voltage discharge lighting signs, as well as sheaths of cables should
be permanently connected to protective conductors and effectively
earthed.
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