How To Install Underground Cable

Tips on Running Electrical Lines Underground

Underground Electric Cables
Jared Earle/Creative Commons/Flickr

It is not particularly hard to run underground cable to a detached garage or other outbuilding, especially if you have some basic wiring experience. If you just need to add some lighting and a few outlets, you can tap into an existing circuit in the house. For bigger electrical needs, though, plan to run a circuit or two from the service entrance panel to a subpanel mounted in the garage. If you are not sure what your future electrical needs might be in the garage, install the subpanel.

You may want to hire an electrician to handle wiring connections in the house and garage. But you can still save a lot of money on the project by digging the trench yourself and installing underground conduit.

Use the Right Type of Cable

When running underground cable, the only kind of cable to use is type UF (underground feeder) electrical cable.

Types of Conduit

When running electrical wiring underground, type UF cable should be routed through rigid conduit. There are two types of conduit that can be used for underground cable. Schedule 40 PVC conduit is the most common and affordable choice. This type of conduit is gray, and it is joined with PVC cement. You can also use rigid metal conduit, although it will cost significantly more. Do not use thinwall (EMT) conduit underground. Use conduit that is at least 3/4-inch wide.

PVC conduit needs to be buried at least 18 inches deep unless it will be covered by concrete, in which case it can be buried 12 inches deep.

Rigid metal conduit can be buried as little as 6 inches deep, with or without a concrete cap. Be sure to check with your local code before you start installing underground cable.

Dig a Trench

Use a trenching shovel to dig a narrow channel from the house to the garage. If you have to dig a long trench, you may want to consider renting a trenching machine for this job.

Install the Conduit

PVC conduit can be cut with a hacksaw or PVC saw.
Dry fit all of the pieces along the entire run. Join the pieces of conduit with PVC cement. Run type UF cable through the conduit, and then make the necessary connections in the house and garage. Always check your local building code before you begin running underground cable.