Hi im after some advice on a hot tub install. The house has a split load 16ed CU without non-rcd protected ways. I have run 30m of 6mm SWA from a spare way of the CU which (as i mentioned already) is DP RCD protected. I plan take the SWA to an insulated CU (enclosure) in the garden where I will isolate the TN-S earth (armour) by a nylon stuffing gland, and adopt a TT system for the hot tub with ocpd. I want a TT system in place to avoid anyone getting tingles due to earth potential differences im sure you understand this. My question really is if im gonna use a TT system for the hot tub, which obviously needs RCD protection, can I rely on the supply boards RCD for this. Ideally I would have wanted to take the SWA feed from a non RCD way (but there is none) or a switch fuse (but there is no room to fit a switch fuse) and have more local RCD protection. I seldom carry out TT installs so thought to ask as im unsure if an RCD on a TN-S system can be utilized to also protect a TT system ? Im assuming not but not but cant seem to fathom why it would not operate. Relying on the split load CU RCD would not cause too much inconvenience in the event of a trip as there is only a washing machine socket and cupboard light on that side of the board, similarly if I need to put another RCD in series with it more local to the hot tub. Thanks for any response