Things You'll Need
Installing conduit under or in concrete slabs protects the wires from the weight and corrosion of the cement. It also allows future expansion of the electrical system by pulling additional wires through the conduit. Ridged, nonmetallic PVC conduit is the right material for this job because it is watertight, inexpensive and easy to work with. When installing conduit under a slab it should be buried in the gravel sub-straight about two inches to provide space between the bottom of the concrete and the PVC.
Hold a chalk line at the start of the electrical run -- pull out the string to the end location of the conduit. Pull the string tight and snap a line to mark the path of the conduit in the gravel base.
Dig a trench deep enough to provide 2 to 3 inches of gravel on top of the pipe along this line with the shovel. Keep the base of the trench as level as possible and remove any large rocks.
Lay the PVC conduit along the bottom of the trench from the starting point to the end point.
Back-fill the trench with the material removed and rake it as flat as possible.
Hand tamper the back filled trench to make it as compact and smooth as possible. Avoid damaging the PVC conduit by tampering overly hard.
Do not use a mechanical tamper over the conduit. The additional weight and force may break the pipe.