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The easiest and preferable cable route is below the floorboards. However concrete flooring can often mean that all cable routes have to be installed inside the wall plaster or behind skirting boards. When planning a cable, remember to avoid sharp bends if possible.
Depending on the individual situation you will need to prepare the cable route. This step could involve: chasing in plaster, fitting a mounting box (see Installing an electrical mounting box) or running or crossing along joists. When measuring the length of cable required, allow extra to avoid having to pull it tight along the length of its run.
Laying cable beneath a floor
There will inevitably be parts of the route that will involve the cable being at right angles to the joists. When this is the case, lift the appropriate floor boards to give a clear view.
The joists will have to be drilled approximately 50mm (2 inches) from the top, large enough for the cable to be able to get through. When the holes have been drilled, threadle through the length of cable.
If the cable is running alongside one of the joists, it will still need securing. This can be done by hammering clips into the joist every 250mm or so (10 inches) to hold it in place.
Routing the cable behind plaster
The cable can be run horizontally or vertically but never diagonally - and cannot be routed through thermal plasterboard.
When running cable behind plaster it should be run in oval PVC conduit.
Use a pencil to mark on 2 lines approximately an inch apart so that the planned route can easily be seen.
If you are unsure, then use a wiring detector or bradawl to check that the route will not come into contact with any other pipes or cables in the wall. When you are ready to begin, lightly cut along the lines you have drawn with a sharp knife.
Next you should use a masonry chisel and hammer to chip out the plaster between the lines. It is advisable here to wear safety goggles.
Make sure that the chiselled space is deep enough to hold the cable and for a layer of plaster to cover it. (A plaster covering of 6mm (1/4 inch) should be sufficient to produce a sturdy fill for the wall.
If your route leads you behind a skirting board then it should be possible to chisel away the cable space behind it without having to remove it completely.
Position the cable in the channel and fix it into place using the galvanised nails. Don’t forget to leave enough cable to be able to reach the mounting box.
Add the finishing touches by neatly plastering over the cable in the wall.