Perhaps you have built a shed or a garage and it needs an outlet receptacle, or perhaps you would like to install an electrified lamppost to spruce up the front walk. You can run electricity underground with electrical conduit. Conduit is a system of pipes -- usually metal but more commonly PVC plastic -- used to house electrical wiring. The conduit provides protection for the electrical wiring. PVC conduit is inexpensive and easily installed. Use the grey-coloured PVC conduit graded for outdoor electrical use.
Plan the run of conduit. Measure the distance of the run of conduit from the service entrance in the house to the exterior placement. You may choose to tap into an existing electrical receptacle as long as the new wiring will not overload the circuit. Draw your plan on the paper. Check your plan twice, and remeasure to ensure proper measurement.
Locate the area of the service panel or receptacle inside the house; measure carefully so that you are close to the power source but will not drill through it. From the outside of the house, drill a hole with a spade bit slightly larger then the diameter of your conduit. Drill the hole through the wood rim joist and not through the concrete foundation or through the first floor of the house.
Take a length of PVC pipe and insert it into the hole. Leave 2.5 cm (1 inch) of the pipe extending into the inside of the building. Mark the pipe where it exits the exterior side of the building; with a hacksaw, cut the pipe at this mark. Remove the burrs on the end of the pipe and wipe with a clean, dry cloth.
Go to the inside of the house at the location of the new pipe. Wipe the end of the pipe with a clean, dry cloth.
Remove the knockout from the back of a PVC junction box. Apply PVC cement solvent to the end of the PVC pipe. Insert the conduit into the junction box. Turn the pipe one quarter of a turn to spread the solvent. Allow the joint to set for 5 to 10 minutes.
Go to the exterior side of the PVC pipe to install the LB fitting. Apply PVC cement solvent to the end of the PVC pipe. Insert the pipe into the LB fitting. Turn the LB fitting one quarter of a turn and back again, to spread the solvent. Allow the joint to set for 5 to 10 minutes.
Dig a trench 60 cm (2 feet) deep and about 20 cm (8 inches) wide, directly centred below the exterior LB fitting to the location of the end of the conduit run.
Lay more conduit pipe from the exterior LB fitting to the bottom of the trench. Use joint fittings and cement to secure the sections together. Allow 5 to 10 minutes for the cement to cure.
Using a masonry bit, drill into the house foundation 7.5 cm (3 inches) below the soil line. Attach a conduit strap to the PVC conduit pipe and screw in a masonry anchor screw. This will secure the conduit to the foundation of the house, and prevent the pipes from shifting underground.
Continue to lay more conduit pipe along the length of the trench to the end of the run. Use joint fittings and cement to secure the sections together.
Install the final LB fitting at the end of the run of conduit. Apply PVC cement solvent to the end of the PVC pipe. Insert the conduit into the LB fitting. Turn the LB fitting one quarter of a turn and back again, to spread the solvent. Allow the joint to set for 5 to 10 minutes.
Secure the conduit to the foundation of the building if you are installing an exterior receptacle. Drill a small hole in the foundation, 7.5 cm (3 inches) below the soil line as you did for the first LB fitting. Use a masonry bit if the material is concrete. Attach a conduit strap to the PVC conduit pipe and screw in a masonry anchor screw.
Call the building inspector to inspect your work before filling in the trench.
- The Complete Photo Guide to Home Improvement, Black and Decker, 2009
- New Complete Do-It-Yourself Manual, Reader's Digest, 1991
- City of Saint Paul: Residential garage wiring
- Always run green grounding wire when using PVC conduit.
- Call a professional licensed electrician if you are unsure of your abilities.
- Loads for circuits vary, depending on the number and amperage of the existing receptacles and wires and the load capability of the circuit breaker.
- Call your utility company or local planning department before digging a trench. Inform them of the location of your trench, and have them check for existing underground cables and pipes.