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

(vi) Except as provided by (vii) where the supply to an electrode
water heater or electrode boiler is single phase and one
electrode is connected to a neutral conductor earthed by the
electricity supplier, the shell of the water heater or boiler should
be connected to the neutral of the supply as well as to the
earthing conductor.
(vii) Where the heater or boiler is not piped to a water supply or in
physical contact with any earthed metal, and where the
electrodes and the water in contact with the electrodes are so
shielded in insulating material that they cannot be touched
while the electrodes are live, a fuse in the phase conductor may
be substituted for the circuit breaker required under (ii) and the
shell of the heater or boiler need not be connected to the
neutral of the supply.
(b) Heaters for liquids or other substances, having immersed heating
elements
Every heater for liquid or other substance should incorporate or be
provided with an automatic device to prevent a dangerous rise in
temperature.
(c) Water heaters having immersed and uninsulated heating elements
(i) Every single phase water heater or boiler having an uninsulated
heating element immersed in the water should comply with the
requirements of (ii) and (iii). This type of water heater or boiler
is deemed not to be electrode water heater or boiler.
(ii) All metal parts of the heater or boiler which are in contact with
the water (other than current carrying parts) should be solidly
and metallically connected to a metal water pipe through which
the water supply to the heater or boiler is provided, and that
water pipe should be connected to the main earthing terminal
by means independent of the circuit protective conductor.
(iii) The heater or boiler should be permanently connected to the
electricity supply through a double-pole linked switch which is
either separate from and within easy reach of the heater or
boiler or is incorporated therein and the wiring from the heater
or boiler should be directly connected to that switch without
use of a plug and socket outlet; and, where the heater or boiler
is installed in a room containing a fixed bath, the switch should
also comply with Code 26A(3).
(iv) Before a heater or boiler of the type referred to in subparagraph
(c) is connected, the electrical worker should confirm that no
single-pole switch, non-linked circuit breaker or fuse is fitted in
the neutral conductor in any part of the circuit between the
heater or boiler and the origin of the installation.
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