Some great advice from the guys there , one thing that springs to my mind is has there been a recent periodic done on the installation , only reason im asking is do you know the ring conditions all readings are satisfactory etc , it is great to see an installation being checked on a regular basis , but if there are some defects on the rings etc open circuits on rings etc it could demine the tests you are carrying out , if a periodic had been carried out at the tests were all ok then great idea makes sense , dont mean to be negative and its just a thought , oh the other test you could to is the ramp test of the RCD to mkae sure its tripping at the required ma rating