Paul,
Many thanks for your reply. I am aware of the points you have made and I concur. I always take r1+r2 values and ensure neutral is earth referenced ( amazing the number of even large ups units that are not installed so! On an earth fault the collapse of voltage to the load caused by the ups current limiting protection may be the reason that earth fault loops are apparently high. I know that most people would not take earth loop readings as a rule on such circuits but I would have liked to compare notes or discuss the actual cause.
