Low resistance ohmmeter
Instruments to BS EN 61557-4 will comply.
Basic instrument accuracy required is +/- 5%
Test voltage ac or dc, between 4 V and 24 V
Test current not less than 200 mA
Able to measure to within 0.01 Ohms (resolution of 0.01)
May be the continuity range of an insulation resistance tester.
Insulation resistance tester
Direct test voltage depends on the circuit under test, but will be:-
250 V for extra-low voltage circuits
500 V for other circuits supplied at up to 500 V
1000 V for circuits rated between 500 V and 1000 V.
Must be capable of delivering a current of 1 mA at the minimum allowable resistance level, which is:-
250 kOhms for the 250 V tester
500 kOhms for the 500 V tester
1 MOhms for the 1,000 V tester
Basic instrument accuracy required is +/-5%
Must have a facility to discharge capacitance up to 5 microF which has become charged during the test
May be combined with the low resistance ohmmeter
Earth-fault loop impedance tester
Instruments to BS EN 61557-2 will comply
Must provide 20 to 25 A for up to two cycles or four half-cycles
Basic instrument accuracy required is +/-5%
Able to measure to within 0.01 Ohms (resolution of 0.01)
Instruments to BS EN 61557-3 will comply
Residual current device (RCD) tester
Must perform the required range of tests (see (8.6.3))
Suitable for standard RCD ratings of 6.10, 30, 100, 300 and 500 mA
Must NOT apply full rated test current for more than 2 s
Currents applied must be accurate to within +/-10%
Able to measure time to within 1 ms (resolution of 1)
Must measure opening time with an accuracy of +/-5%