DS-05Check the mounting box and re-fix it if it's looseMost switch boxes are already fixed in the wall, so you won't normally need to drill. If the box wobbles or the old fixing screws have stripped, you'll need to refix it, and the right fixing depends on the wall. In solid brick or block, use a 5mm masonry drill bit, insert a 5mm wall plug, and use a 3.5 x 30mm screw. In plasterboard on timber studs, drive a 3.5 x 30mm wood screw straight into the centre of the stud - use a magnet or stud detector to find it, and expect solid resistance and timber dust from a small pilot hole. In plasterboard on metal studs, never use a plain wall plug or wood screw - it strips straight through 0.5mm steel; use a self-drilling metal-stud fixing instead, and check for fine steel swarf from a pilot hole to confirm you've found a metal stud. On dot-and-dab plasterboard, use a fixing long enough to pass through the board and adhesive dabs and bite into the masonry behind, typically 60-75mm. On lath and plaster, screws can pull through the lath - use a suitable plasterboard-and-plaster fixing, or screw into a joist or stud if one is close by. Before drilling anywhere, use a cable and pipe detector, then still treat the wall as if something's there until you've checked with a small test hole - detectors miss cables in metal conduit, behind metal-backed board, or outside standard safe zones. Keep the circuit off at the consumer unit while you do this.