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

21B Testing of Low Voltage Installations
(1) Safety
Precautionary measures should be taken during testing and the method
of tests should be such that no danger to persons or property can occur
even if the circuit being tested is defective.
(2) Sequence of tests
(a) The following items, where relevant, are to be tested preferably in
the sequence indicated below:
(i) continuity of protective conductors, including main and
supplementary equipotential bonding,
(ii) continuity of ring final circuit conductors,
(iii) insulation resistance,
(iv) polarity,
(v) earth electrode resistance,
(vi) earth fault loop impedance,
(vii) functions of all protective devices,
(viii) functions of all items of equipment.
(b) In the event of any test indicating failure to comply, that test and
those preceding, the results of which may have been influenced by
the fault indicated, should be repeated after the fault has been
rectified.
(3) Continuity of protective conductors
Every protective conductor, including all conductors and any extraneous
conductive parts used for equipotential bonding should be tested for
continuity. The test should be made by connecting together the neutral
and protective conductors at the mains position and checking between
earth and neutral at every outlet by a continuity tester, which should
show a reading near zero.
(4) Continuity of ring final circuit
(a) The ring circuit should be tested from the distribution board. The
ends of the two cables forming the phase conductor should be
separated, and a continuity test should show a reading near zero
between the two; the same tests to be made between the two
cables that form the neutral conductor, and between the two cables
that form the protective conductor (see Figure 21(1)).
(b) The testing method in subparagraph (a) above is only applicable
when the ring circuit has been inspected throughout, prior to the
test, to ascertain that no interconnection (multi-loops) exists on the
ring circuit. Otherwise, the testing methods stipulated in Part 3 of
the Guidance Note 3 to BS7671, should be adopted instead.
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