54 Wiring Systems and Fault Finding For Installation Electricians Table 3.1 Test
Range
Type of Instrument
1
Continuity of ring final conductors
0.05–0.8 Ω
Low reading ohmmeter
2
2–0.005 Ω or less
3
Continuity of protective conductors Earth electrode resistance
4
Insulation resistance
Any value over about 3 or 4 Ω Infinity to less than 1 MΩ
Low reading ohmmeter Special ohmmeter
5 6 7 8
Polarity Earth fault loop impedance Operation of RCD Prospective fault current
None 0–2000 Ω 5–500 mA 2 A–20 kA
High reading ohmmeter Ohmmeter, bell, etc. Special ohmmeter Special instrument Special instrument
SELECTION OF TEST INSTRUMENTS It is clearly most sensible to purchase instruments from one of the established manufacturers rather than to attempt to save money by buying cheaper, lesser known brands. Also, as the instruments used in the world of installation are bound to be subjected to harsh treatment, a robust construction is all important. Reference should be made to the HSE Guidance Note GS38 ‘Electrical test equipment for use by electricians’. Many of the well-known instrument companies provide a dual facility in one instrument, for example PFC and loop impedance, or insulation resistance and continuity. Hence it is likely that only one, three or four instruments would be needed, together with an approved test lamp (a subject to be dealt with in the next section). Now, which type to choose, analogue or digital? There are merits in both varieties, and the choice should not be determined just by expense or a reluctance to use ‘new-fangled electronic gadgetry ’! This attitude has, however, become a thing of the past, and an
