How To Run Underground Wiring to a Garage

Running underground wiring to a detached garage can provide power for lighting, tools, and other electrical needs. This project requires the involvement of a licensed electrician to ensure safety and compliance with local codes. However, there are some steps that homeowners can undertake themselves. This Old House electrician Scott Caron demonstrates the key steps involved in bringing power to a detached garage safely and efficiently.

Underground Wiring Planning and Preparation

Proper planning and preparation are essential before beginning any electrical work. This ensures safety, compliance with local regulations, and a smooth installation.

Obtaining Permits and Inspections

Contact your local building department to determine the necessary permits for running underground wiring to your garage. Most jurisdictions require electrical permits and inspections for this type of work.

Calling Utility Companies

Contact your local utility company to mark underground pipes and wires before you start digging. This helps prevent accidental damage to utilities and ensures the safety of workers during the trenching process. Most areas have a centralized “call before you dig” service that will coordinate with various utility companies to mark their lines.

Trenching and Cable Installation

The first major step in running underground wiring to a garage is creating a trench and laying the cable. Careful attention to depth and routing will ensure a safe and code-compliant installation. If you don’t feel completely comfortable with a given step, call a professional electrician.

Digging the Trench

Rent a gas-powered trenching machine to dig a trench at least 12 inches deep from the house to the garage. This depth is typically sufficient for most residential applications, but check your local codes for specific requirements. Prepare for some manual digging around obstacles or in tight spaces.

Laying the Cable

After digging the trench, lay the UF (underground feeder) cable. This specialized cable can withstand direct burial and moisture exposure. UF wire has a waterproof sheathing, allowing you to bury it directly in the earth without additional protection in most cases.

Installing Conduit

While you can bury UF cable directly in the ground, you must protect any exposed portions above ground with conduit. At both the house and garage ends, install a three-quarter-inch-diameter plastic conduit to shield the cable where it emerges from the ground and enters the structures. Use a propane heat gun to bend the conduit as needed to conform to the foundation or wall contours.

Connecting to the House

Properly connecting the underground wiring to your home’s electrical system is crucial for safety and functionality. Contact an electrician if you run into any issues.

Creating an Entry Point

Use a drill with a one-and-a-half-inch hole saw bit to create an entry point through the house wall into the basement. Position this hole directly above the end of the trench. This lets you feed the cable from the trench into the house.

Running Cable to the Electrical Panel

From inside the basement, pull the cable all the way to the main electrical panel. Secure the cable to the overhead joists using cable staples to keep it neat and out of the way. Make sure you adhere to code requirements for cable routing and support.

Garage Connections

The final steps involve bringing the power into the garage and setting up the necessary electrical components. You’ll need a licensed electrician to complete the final hookups.

Running Cable to the Garage

Follow the same process as before to feed cable through a conduit into the garage. After feeding the cable into the garage, screw the conduit outlet body to the exterior wall of the garage. Screw the other conduit body to the house wall. Apply exterior-grade acrylic-latex caulk around the conduit outlet body to seal out water.

Installing a Subpanel

You may want to install a subpanel in the garage to distribute power to various circuits. This subpanel allows for easier management and provides a convenient shutoff point. Contact a licensed electrician for help installing a subpanel.

Setting up GFCI Protection

Because the wire is buried 12 inches deep, you may want to protect the circuit with a GFCI (Ground Fault Circuit Interrupter) breaker. This safety device helps prevent electrical shocks by quickly shutting off power when it detects a ground fault.

Connecting Outlets and Lighting

With the subpanel in place, you can plan the outlet and wiring connections in your garage. Lay out an idea of the wiring in your garage, then contact a licensed electrician to handle the hookup.

Finishing the Installation

Complete these final steps to ensure the long-term safety and functionality of your wiring.

Backfilling the Trench

Backfill the trench after laying the cable. Start by covering the cable with about two inches of sand to provide a protective cushion. Next, lay caution tape along the entire length of the trench. This serves as a warning for anyone digging in the area.

Patching and Sealing Entry Points

Once you’ve connected your wiring and backfilled the trench, inspect where the cable enters the house and garage. Use weatherproof sealant to patch any gaps around these entry points. This will prevent moisture entry, which could compromise the integrity of your electrical system.

Final Inspections

Once all connections are secure, schedule a final inspection with your local building department. This inspection will verify that all work meets code requirements and is safe for use. Don’t energize the new circuit until it has passed inspection.

Additional Safety Measures

Maintaining the safety of your electrical installation extends beyond just the wiring and components.

Using Caution Tape

Lay caution tape along the entire length of the trench before backfilling. This tape serves as a warning for anyone who might dig in the area in the future and can help prevent unintentional damage to the buried cable.

Installing Proper Lighting

Proper lighting in and around the garage can enhance safety, especially during nighttime. Consider installing motion-sensor lights at the entry points and adequate lighting inside. Well-lit areas deter potential intruders and reduce the risk of accidents.

Regular Maintenance and Inspection

Regularly inspect the underground wiring and associated components. Look for signs of wear, water damage, or any other issues that could compromise the system’s integrity. Address any concerns promptly to maintain a safe and functional electrical system.