I'm a homeowner with no electrical skills. BG electrician came to repair something & said my fuse board is not to standard as it only has one RCD. The property was built in 1874 and most of the current systems were put in place in the 1980s. Lived here 24 years & the tripping mechanism works brilliantly. In my basic understanding you can't have two RCDs on one circuit & he was using modern regulations and applying them to my old property, which can't be done retrospectively, am I right? I am trying to sell, will this be an issue on survey & if so, what will it cost to correct. Thanks