How to Run a Circuit Underground to a Garage

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Power up a detached garage by running an electrical line to the building.
Power up a detached garage by running an electrical line to the building. (Image: Jupiterimages/Photos.com/Getty Images)

Running an electrical cable to the garage eliminates such inconveniences as powering a garage with an overhead power line, or having no electricity in the building. You have some choices with respect to the conduit inside which the cable runs. Those choices are a tradeoff between the depth you bury the cable and the cost of the material that makes up the conduit.

Preparation

Before considering an underground electrical run, call the utility companies. Those organizations often have buried pipes and cables running beneath your yard. Many states and communities have a one-call phone number that informs all the local utilities that you plan to dig. The companies send representatives who mark the locations of underground utility lines so you know which areas to avoid. Lay out your trenching plans so you avoid these utilities while still running as straight a line as possible from the point where the cable will exit your home to the point where it will enter the garage. Check your local building codes for regulations about wiring buildings.

Conduit Choices

Your choice of conduit depends on how deep you wish to dig. Local building codes, along with soil conditions, also influence digging plans. Protect electrical wires with rigid, galvanized metal conduit for trenches 6 inches deep. Metal is a more expensive option than other materials, and the wires themselves need to be waterproof. Run the same type of waterproof wires through polyvinyl chloride conduit if you’re willing to dig down to an 18-inch depth. Select direct-bury UF-B cable if you can dig down 24 inches. This cable needs no conduit except for where it is exposed entering the home and garage, and to 18 inches below ground level.

Laying Cable

A short run of a shallow, 6-inch trench in loose soil can be dug with little more than a shovel. Deeper trenches typically require the power of a trench digger, a machine you can rent. Spray paint the path from the home to the garage, avoiding tree roots as well as the utility lines. Once the trench is open to the required depth, lay the cable or conduit inside the trench. Slip stiff electrical cable or wires through the inside of the conduit once it’s laid at the bottom of the trench. Pull out several feet of cable on the other end to give you enough wire for the necessary connections.

Making Connections

Add an “ell” fitting to each end of the run where the cable enters the house and garage. The ell allows access to the wires inside while protecting them at the point where they must make a 90-degree turn into each building. Drill holes into the house and garage so the wires can pass through. Building codes typically require that a licensed electrician make final connections to the main electrical panel. Even if local codes do not call for this requirement, have an electrician connect the wires if you are not trained and experienced in making these types of connections.

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