Turn off the power to the circuit you are working on at the main breaker. Confirm the power is off by touching a noncontact voltage detector to the wire's insulation.
Dig a hole with a shovel where you wish to make the wire splice. The hole should be large enough to accommodate the exterior underground electrical box and deep enough so that the box will be sightly higher than flush with the surface when backfilled.
Strip 3/8 inch of insulation off the conductors for the two wires you wish to join.
Insert one wire through an access hole in the side of the electrical box and pull 6 inches of wire into the box. Secure the wire in place by tightening down the wire clamp with a screwdriver. Consult the exterior electrical box's manual for the method to seal the access hole from moisture penetration. Repeat this process to bring the other wire into the box.
Twist together the like-colored wires with pliers and install exterior underground wire nuts on each connection.
Push the wires into the electrical box and place the cover on top. Secure the cover to the box by tightening the four screws with a screwdriver.
Place the box in the hole so the top of the box is slightly above the surface. Backfill the hole with soil, keeping the box's cover exposed.
Things You Will Need
- Noncontact voltage detector
- Underground exterior electrical box
- Underground exterior wire nuts
- Wire strippers
- Choose a location for your wire splice that eliminates the chances of mechanical damage from lawnmowers, automobiles or people walking around the property.