Instruments insulation tester

Combined inspection and testing is also necessary on some equipment because some faults cannot be seen by just looking - for example, the continuity and effectiveness of earth paths on class I equipment. For some portable appliances the earth is essential to the safe use of the equipment and, therefore, all earthed equipment and most extension leads should be periodically tested and inspected for these faults. All portable appliance test instruments (PAT Testers) will carry out two important tests earth bonding and insulation resistance. 

BS 7671 specifies that d.c. test voltages should be used for insulation resistance tests, and that the minimum acceptable insulation resistance values should be in accordance with Table 17.1. The instruments used should be capable of providing an output of not less than 1 mA. For installations designed to operate at voltages up to 500 V, e.g. those connected to the 400/ 230 V public supply and the 110 V systems supplying portable apparatus, a 500 V d.c. insulation tester is adequate and suitable for the prescribed test. A 1000 V tester should be used to test systems over 500 V up to 1000 V. Large installations should be tested in sections, each of not more than 50 outlets. An outlet, for example, consists of a lighting point, a switch or a socket outlet. 

There must also be a range of instruments including insulation testers, multimeters, potential indicators, loop impedance testers, RCD testers, current transformers, wattmeters and perhaps relay testing equipment. Expensive instruments, such as oscilloscopes, which may be only occasionally required and which may require expert handling are probably not worth buying, but can be hired when needed or can be provided by a specialist called in to deal with a problem that cannot be tackled in-house. 

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