to the 16th Edition IEE Regulations

chapter 5

chapter 6

Inspection and Testing
  8.1 - Introduction 8.5 - Insulation tests
  8.2 - Inspection 8.6 - Earth testing
  8.3 - Testing sequence 8.7 - Test instrument requirements
8.4 - Continuity tests 8.8 - Supporting paperwork

8.4.3 - Correct polarity

If a single-pole switch or fuse is connected in the neutral of the system rather than in the phase, a very dangerous situation may result as illustrated in {Fig 8.8}.

Fig 8.8 - The danger of breaking the neutral of a circuit

Fig 8.9 - Polarity test of an installation

It is thus of the greatest importance that single-pole switches, fuses and circuit breakers are connected in the phase (non-earthed) conductor, and verification of this connection is the purpose of the polarity test. Also of importance is to test that the outer (screw) connection of E S lampholders is connected to the earthed (neutral) conductor, as well as the outer contact of single contact bayonet cap (BC) lampholders. The test may be carried out with a long wander lead connected to the phase conductors at the distribution hoard and to one terminal of an ohmmeter or a continuity tester on its low resistance scale. The other connection of the device is equipped with a shorter lead which is connected in turn to switches, centre lampholder contacts, phase sockets of socket outlets and so on. A very low resistance reading indicates correct polarity (see {Fig 8.9}).

To avoid the use of a long test lead, a temporary connection of phase to protective systems may be made at the mains position. A simple resistance test between phase and protective connections at each outlet will then verify polarity. In the unlikely event of the phase and protective conductor connections having been transposed at the outlet, correct polarity will still be shown by this method; this error must he overcome by visual verification -

Don't forget to remove the temporary connection afterwards!

Special care in checking polarity is necessary with periodic tests of installations already connected to the supply, which must be switched off before polarity testing. It is also necessary to confirm correct connection of supply phase and neutral. Should they be transposed, all correctly-connected single-pole devices will be in the neutral, and not in three phase conductor.

            One practical method of checking polarity and continuity of ring or radial circuits for socket outlets is to connect two low power lamps to a 13 A plug. One is connected between phase and neutral, and the other between phase and earth. Plugging in at each socket tests correct polarity and the continuity of live and protective conductors when both indicators light. It is important where RCD protection is employed to use very low power indicator lamps such as neon or LED devices (with suitable current limiting resistors where necessary). The smallest filament lamp will take sufficient current from phase to earth to trip most RCDs.



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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations