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I can see that when testing insulation resistance you may want to use DC so it is not showing current through a capacitor to get the 1MΩ required under the old BS7671:2008 rules. However for practical purposes, what we want, is to be sure when a RCD is controlling the circuit it will not trip the RCD so in real terms it would be better to test with 250 V ac at 50 Hz so any surge protective devices (SPD) which could cause enough leakage to cause the RCD to trip are highlighted?
Odd at 500 and 1000 volt the old BS7671:2008 does not say DC or AC only at 250 V is it stipulated dc, my old meter does not have an option to test with AC but it is old, and at that time 1980 we did not have that many RCD's around, not seen a AC/DC switch on a meter, but maybe today that is a required option?
Odd at 500 and 1000 volt the old BS7671:2008 does not say DC or AC only at 250 V is it stipulated dc, my old meter does not have an option to test with AC but it is old, and at that time 1980 we did not have that many RCD's around, not seen a AC/DC switch on a meter, but maybe today that is a required option?