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

(d ) Single phase domestic thermal storage or instantaneous water
heaters not exceeding 6 kilowatts should be connected to an
individual final circuit and be controlled by a double-pole switch of
adequate rating. If the water heater is installed in a bathroom, the
double pole switch should be installed outside the bathroom in a
convenient position.
(e) A thermal storage or instantaneous water heaters exceeding 30
ampere or having a current rating exceeding half of the maximum
demand of an installation in any one phase, should be connected to
a three phase supply except when approved by the electricity
supplier.
(6) Electrical call bells and electric clocks
(a) (i) Call bell transformers should be double wound.
(ii) Call bell transformers should be connected via a plug and
socket arrangement or via a connection unit or cable coupler.
(iii) Call bell pushes should be wired to the secondary windings at
an extra low voltage.
(b) Electric clocks may be connected to a lighting circuit via a connection
unit or cable coupler provided that the current demand of the circuit
does not exceed the rating of the overcurrent protective device.
26B Busbar Trunking Distribution System
(1) General
(a) The busbar trunking system should comply with IEC 60439-2 / BS EN
60439-2 and should be properly supported.
(b) The busbar trunking system must be suitable for branch circuit
connections to the busbars by tap-off units or cable clamping
devices.
(c) The cross-sectional area of phase and neutral conductors of the
busbars system should be selected taking into account the effects of
harmonic current that may be present in the distribution system.
(2) Busbar casing
(a) The casing of the busbar trunking system should be totally enclosed.
It should be rigidly constructed from sheet steel galvanised or
suitably protected against corrosion of not less than 1.2 mm thick
for the width or height of the casing not exceeding 100 mm; and
not less than 1.5 mm thick for a width or height exceeding 100 mm.
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