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

(f ) Every safety source and isolating source, other than an electrochemical
source (e.g. a battery) or another source independent of a
higher voltage circuit (e.g. an engine driven generator), should be
situated outside the restrictive conductive location, unless it is part of
a fixed installation which satisfies subparagraph (a) above within a
permanent restrictive conductive location.
26O Installation of Equipment Having High Earth Leakage
Currents
(a) The particular requirements of this Code should apply to every installation
supplying equipment having a high earth leakage current (usually
exceeding 3.5 mA), including information technology equipment to IEC
60950 and industrial control equipment where values of earth leakage
current in normal service permitted by recognised standards necessitate
special precautions being taken in the installation of the equipment.
(b) Where more than one item of stationary equipment having an earth
leakage current exceeding 3.5 mA in normal service is to be supplied
from an installation incorporating a residual current device, it should be
verified that the total leakage current does not exceed 25% of the
nominal tripping current of the residual current device.
Where compliance with this Code cannot be otherwise achieved, the
items of equipment should be supplied through a double-wound
transformer or equivalent device as described in paragraph ( f )(vi) of this
Code.
(c) An item of stationary equipment having an earth leakage current
exceeding 3.5 mA but not exceeding 10 mA in normal service should
either be permanently connected to the fixed wiring of the installation
without the use of a plug and socket outlet or should be connected by
means of a plug and socket outlet complying with IEC 60309-2 or
equivalent.
(d ) An item of stationary equipment having an earth leakage current
exceeding 10 mA in normal service should preferably be permanently
connected to the fixed wiring of the installation. Alternatively, one of the
following precautions should be taken:
(i) the equipment may be connected by means of a plug and socket
outlet complying with IEC 60309-2 provided that the protective
conductor of the associated flexible cable is supplemented by a
separate contact and a second protective conductor having a
cross-sectional area not less than 4 mm 2 or the flexible cable
complies with paragraph ( f )(iii) of this Code with the second
protective conductor connected via a separate contact within the
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