-
Twin and earth has kinda always bothered me as a slightly lazy approach. In the UK its a hard enough time getting 'qualified electricians' to even realise that switching neutral and live at every other point isn't good practice, actually fitting earths to things that should have them is defo a requirement (metal lights, metal back boxed sockets etc) and maybe not holding a 10kw shower cable to the wall by nailing through the centre of it (nailing the earth) to as many different items in a house is also not good. When you question them on these things you'll get the age old 'thats the way i've always done it' retort.
Recently had to pretty much fully rewire my mums house as there was at least 10 points at which the danger level was at the point that if any actually good electrician came in, they would be condemning the structure and using the place as a case study. Lighting circuit was something out of a horror story, in one place I found a nail had been put through some hardboard/plasterboard and the switched neutral for that end of the house was joined by 'hanging it' on the nail from the inside of the wall. On the outside of the wall a picture hung on that nail. Nice surprise! No earths actually really worked, faults and high resistance readings basically everywhere. Phases swapped (3 phase supply, badly utilized into a single phase supply) at every opportunity. 4 ring mains, all of which were crossed with at least one other in some way (neutral or live borrowed into another circuit at random locations). Massively undersized cable in some places, massively oversized cable in others (shower wire being used for lighting circuit). RCD/sensing breakers all wrong types for the duty and just hammered into the consumer unit. Took me 4 days of trying to untangle it before deciding it was too crazy to deal with and replacing everything. 15 days total, no more random trips, blown bulbs and consumer devices blowing up.
In France we don’t have ring mains. Every circuit is radial, and has an RCD and circuit breaker on the consumer unit. Twin & earth is illegal as earths must also be insulated and as big a cable as the other two. Switching is on the neutral wire. There are so many cables!
That’s if your house is up to the normes. Usually you find the most dangerous lashed up mess and have to rip it all out.