26-11-2015, 05:49 PM
Sounds like your earth loop impedance is already safe enough if it trips on a 7k rsistor.
I just thought up this idea so it may be utter rubbish but it seems to make sense. You can do a more sensitive test by finding the highest value resistor that will trip the RCD when connected from L in to N out. Or N in to L out. This is what the test button does but you are trying to find the trip threshold. Then find the highest value that will trip when connected from L to the earth rod. This should be lower than the value found in the first test. To a fair approximation the difference is the earth loop impedance.
I just thought up this idea so it may be utter rubbish but it seems to make sense. You can do a more sensitive test by finding the highest value resistor that will trip the RCD when connected from L in to N out. Or N in to L out. This is what the test button does but you are trying to find the trip threshold. Then find the highest value that will trip when connected from L to the earth rod. This should be lower than the value found in the first test. To a fair approximation the difference is the earth loop impedance.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
