Running electrical wires to outdoor lights and appliances may require the use of an electrical rigid conduit to protect the wire. Some applications, like patio lights, can use UF wire that is specially insulated for outdoor use and is commonly buried at a depth of 4 inches or less. Other applications, where a higher voltage is carried or where maintaining uninterrupted power is of great importance (such as to pumps or condenser units), install outdoor electrical rigid conduit to run the wire through to protect it from weather, traffic or other potentially damaging occurrences.
Call the local building authority to gather information on any necessary permits or installation requirements. Arrange for the local utility companies to come out and mark the location and depth of any underground utilities. This is a service that is provided for free in many areas.
Measure and mark where the electrical wire will pass into the building on the inside and outside of the building with a tape measure and pencil. Make sure to check the placement of the point to make sure it is not blocked by any pipe, wire or stud. Drill through the barrier wall, using a paddle bit to make an opening large enough for the wire to pass through.
Place the conduit termination box on the wall and screw it into position, using the drill to drive the masonry or wood screws (depending on the wall type) through the moulded mounting wholes on the box. Apply weatherproof caulk around the edges of the box and the heads of the screws.
Lay out the rigid conduit on the ground from the point where it will pass through into the building to where it will terminate. Place a conduit connector between the sections of the pipe, wherever they will be needed to join two pipes together.
Bend one extra piece of pipe, using a PVC pipe bender (hot or cold), by following the instructions provided with the unit to make the connecting conduit that will rise from the conduit and be buried underground and connect to the terminating box. The bend should be 1 foot in from one end of the conduit, at a 90-degree angle. Leave the remainder of the pipe length as is for now.
Tie one end of the twine to a stable object inside the building and pass the other end through the opening in the barrier wall and out the conduit termination box. Pull the string through the PVC pipe and connectors, beginning with the bent piece, until it has reached the termination end. Tie an object to the terminating end of the twine so it cannot be pulled back into the conduit.
Connect the conduit pieces by coating each end of the pipe and the inside of the connectors with PVC adhesive and pushing the connectors onto the pipe until all the pieces are joined as one unit.
Dig a trench at least 24 inches deep and 6 inches wide unless otherwise specified by the building code for the entire run of the pipe.
Untie the twine that is anchored inside the building and knot it securely to one end of the electrical wire to be run through the conduit. Pull the outside end of the twine until the wire is run through the entire length of conduit and appears out the terminating end. Untie the twine and discard it.
Lower the conduit into position. Bend another piece of pipe and attach it to the terminating end of the conduit if the wire needs to rise out of the ground to make the connection to its appliances. Cut the longer end of the bent pieces of PVC to the appropriate height to make the connection to the terminator box and appliance, using a small hacksaw.
Glue the pipes into the connectors on the conduit box or appliance connection point, if applicable, and apply a bead of weatherproof caulk around the joint. Screw in pipe brackets over the conduit to secure the exposed vertical piece to the wall or appliance mounting post, if applicable. Finish the project by connecting the wiring to the power source and appliance.
Add a 4-inch layer of gravel on top of the conduit before filling the trench with dirt. This is added protection for the conduit. Should digging occur later, the gravel will signal the labourer that they have almost dug down to the conduit and should proceed with caution.
Never use electrical wiring rated for indoor use only for outdoor applications even if it is going to be run through a conduit. The risk of a short causing a fire or electrocution is greatly increased, as the wire's insulation is not meant to withstand outdoor conditions.