We recently went through the RCD keeps tripping fault finding loops. Couldn't get repeatable tripping out of the RCD,  endup with getting a sparke to look at it and after a couple of visits (combined with other electrical work on the farm, because 30 kms of travel each way is a tad expensive) turned out to be the dryer (samsung heat pump one) much to my wife's delight new dry and its all gone.