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

(6) Polarity
(a) A test of polarity, as illustrated in Figure 21(6), should be carried out
to verify that:
(i) every fuse and single-pole control and protective device is
connected in the phase conductor only;
(ii) centre-contact bayonet and Edison-type screw lampholders to
IEC 60238 in circuits having an earthed neutral conductor, have
their outer or screwed contacts connected to that neutral
conductor; and
(iii) wiring has been correctly connected to socket outlets and
similar accessories.
(7) Earth electrode resistance
(a) A proper earth electrode resistance tester should be used to measure
earth electrode resistance. An alternating current at 50 Hz of a
steady value is passed between the earth electrode T and an auxiliary
earth electrode T placed at a separation distance recommended by
1
the manufacturer of the tester but in any case should not be less
than 20 metres away. A second auxiliary earth electrode T , which
2
may be a metal spike driven into the ground, is then inserted halfway
between T and T , and the voltage drop between T and T ,
1 2
divided by the current flowing between T and T , gives a measured
1
earth electrode resistance of earth electrode T.
(b) The test method is depicted in Figure 21(2).
(c) For an electrical installation having four or more earth electrodes
which are installed more or less in line, following a general direction
not exceeding 15° deviation and with separation between adjacent
electrodes not less than the recommended distance by the
manufacturer of the tester but in any case not less than 20 metres,
these electrodes can be used in turn as the auxiliary electrodes for
the purpose of measuring the earth electrode resistances, as
illustrated in Figure 21(3).
(d ) The following alternative method for measuring the earth electrode
resistance may be used if the electricity supply is connected. A loop
impedance tester should be connected between the phase
conductor at the origin of the installation and the earth electrode
with the test link open, and a test performed. This impedance
reading could be treated as the electrode resistance.
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