Key points
- BS 7671: unprotected concealed cables run in a 150 mm band at the top of the wall, 150 mm at corners, and vertically and horizontally from switches and sockets.
- Don't assume your electrician followed these zones; use a detector before every hole.
- Avoid drilling directly above and below switches and sockets, and above basins, mixers and bathroom supply lines.
- The wall plug is chosen by wall material (concrete, hollow block, gypsum board), the load, and the plug manufacturer's instructions.
What you need
Tools
- Drill with hammer action for concrete and block walls
- Masonry bits and tile bits
- Cable and metal detector
- Spirit level (laser or standard)
- Tape measure and pencil
- Safety glasses and dust mask
- Vacuum to collect dust
Materials
- Wall plugs and screws suited to the wall type and load
- Masking tape for drilling through tiles
Before any hole, ask two questions: what is behind this wall? and what is this wall made of? The answers decide whether the hole is safe and which fixing you need.
1) Where should you expect cables?
Under the British wiring standard BS 7671, cables concealed in walls without mechanical protection must be within defined zones1:
- A 150 mm strip at the top of the wall where it meets the ceiling.
- A 150 mm strip on each wall at internal and external corners.
- A vertical and horizontal route from each switch, socket or electrical accessory.
Outside these zones the standard requires armoured cable, steel conduit or trunking, or mechanical protection against nails and screws1.
2) Water and drain pipes
- Expect pipes above and below basins, mixers and water heaters, and in straight lines between water points in bathrooms and kitchens.
- Some metal detectors cannot find PPR and plastic pipes; choose a detector that finds more than one type, and don't rely on it alone. See pipe types.
- In floors: don't drill a bathroom or roof floor; you may puncture the waterproofing layer.
3) Choosing a wall plug by wall type
| Wall material | How to recognise it | Common choice |
|---|---|---|
| Solid concrete | Hard drilling, grey dust, and the bit sometimes hits reinforcing steel. | Standard plastic plugs for light and medium loads; metal anchor bolts for heavy loads. |
| Hollow block | The bit suddenly "drops" into a void while drilling. | Plugs designed for hollow materials (they expand or knot behind the wall), or chemical anchors with a sleeve for heavier loads. |
| Gypsum board | Hollow sound when tapped, white dust. | Plasterboard fixings (spiral or folding metal); heavy loads fixed into the metal studs or into backing behind the board. |
Practical guidance table. The safe load of any plug is stated by its manufacturer on the pack or data sheet; follow it, especially for TVs, wall cabinets and anything above a bed or seat.
4) Steps
- Mark the position and measure using the level.
- Scan with the detector around each mark, and avoid the routes above, below and beside switches and sockets.
- Choose the drill bit matching the diameter printed on the plug pack.
- On tiles: put masking tape over the mark to stop the bit slipping, and use a tile bit without hammer action until you are through the tile, then switch to a masonry bit with hammer.
- Hole depth: slightly longer than the plug; clean the dust out of the hole.
- Insert the plug flush with the surface, then fix the item.
Sources
The number next to a statement points to its source in this list. Sources back the general information; anything marked “practical advice” is editorial experience, not a quoted source. Anything that affects safety, structural design or electrical installations needs a licensed professional, and in Saudi Arabia the binding reference is the Saudi Building Code.