I had the zip cord in drywall method in a bathroom, partially buried behind tile. Originally, the bathroom only had a wall light above the sink and somebody wanted a ceiling light pronto.
Back in the 50s and 60s, grossly undersized wiring was extremely common for quickly added sockets in Austria. People clipped all sorts of flex to the wall, including 0.5mm2 low-voltage zip cord with nails driven through the centre, sometimes accidentally hitting the conductor itself.
