A property I recently went to to install a few new lights has a TT supply, there are 2 mains units, both remote from the meter. One had normal tails under the floor and the other had a piece of SWA supplying it. It had a 30ma non-time delayed RCD as the main switch. Now apart from having the wrong type of RCD to cover the tails etc (should be an "S" type) whats the score with using a 2 pole RCD as an isolator switch? I would prefer a normal isolator first.