5.2.2 - TT systems
This arrangement covers installations not
provided with an earth terminal by the Electricity Supply
Company. Thus it is the method employed by most (usually
rural) installations fed by an overhead supply. Neutral
and earth (protective) conductors must be kept quite separate
throughout the installation, with the final earth terminal
connected to an earth electrode (see
{5.5}) by means of an earthing conductor.
Effective earth connection is sometimes
difficult. Because of this, socket outlet circuits must
be protected by a residual current device (RCD) with an
operating current of 30 mA
{5.9}. {Fig 5.4} shows the arrangement of a TT earthing
system.
Fig 5.4 - TT earthing
system
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