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

Code 11 EARTH LEAKAGE AND EARTH FAULT
CURRENTS
11A General
This Code describes one of the means for fault protection: earthed
equipotential bonding and automatic disconnection of supply. Other relevant
methods for fault protection in accordance with IEC 60364, BS 7671 or other
relevant international standard practices are also acceptable.
11B Basic Requirements
(a) The characteristics of the protective devices for automatic disconnection,
the earthing arrangements for the installation and the relevant
impedances of the circuits concerned should be coordinated so that
during an earth fault, the voltages on any exposed conductive parts and
between simultaneously accessible exposed and extraneous conductive
parts occurring anywhere in the installation should be of such magnitude
and duration as not to cause danger. Conventional means of compliance
with the above requirements are given in this Code but other equally
effective means shall not be excluded.
(b) Subparagraph (a) is considered to be satisfied if:
(i) for circuits supplying socket outlets, the circuits are protected by
residual current device having a rated residual current not exceeding
30 mA.
(ii) for circuits supplying only fixed equipment within the equipotential
zone, the earth fault loop impedance at every point of utilisation is
such that disconnection occurs within 0.4 second (note 1).
(iii) for circuits supplying fixed equipment outside the equipotential
zone, the earth fault loop impedance at every point of utilisation is
such that disconnection occurs within 0.2 second (note 2).
(iv) for installations supplied from overhead line system, the installations
are protected against earth leakage by residual current device.
(v) for distribution boards supplying circuits for both socket outlets and
fixed equipment, the impedance of the protective conductor
between the distribution board and the point at which the protective
conductor is connected to the main equipotential bonding does not
exceed 50 Zs/Uo ohms, where Zs is the earth fault loop impedance
corresponding to a disconnection time of 5 seconds; or alternatively,
equipotential bonding provided at the distribution board in
accordance with Code 11E is also acceptable.
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