If you are confident enough in your wiring skills to add an electrical circuit indoors, then running a circuit to a separate outbuilding is something you might be able to do yourself. However, you should be aware that it would necessitate work at the main circuit breaker panel to install and connect one or more new circuit breakers.

Many people prefer to have this type of work done by a professional, and for good reason: work at the main service panel can result in very serious or lethal shock if you don’t know what you’re doing.

Even if you hire an electrician to connect the outlets and light bulbs in your garage and make the final hookups at the service panel, you may save a lot of money on the most labor-intensive phase of the project: laying the underground wire from the house to the garage or outbuilding. By donating your own sweat equity, you will limit the cost of this aspect of the project to the cost of materials.

Wire and Cable for Underground Lines

There are several methods for burying electrical wiring. The depth of the cable will be determined by the method used. The approach you employ may be dependent on what is authorized or recommended by your local Code authorities, so always check with the local building inspections office to find out what is advised in your community. In general, the National Electrical Code allows for three methods of running underground circuits:

Directly laying UF (underground feeder) cable into the earth. This is known as direct burial, and if you do it, the UF cable must be at least 24 inches below the ground’s surface to avoid being perforated by ordinary shoveling. Additionally, the vertical runs where the cable falls into the ground on the house side and emerges from the earth on the outbuilding side must be contained in rigid conduit, often PVC. A sweep fitting is attached to the ends of the vertical conduit at the bottom of the trench, and the cable is snaked through the elbows and up into the conduit on both sides.

Wire is routed through a strong galvanized metal conduit. The conduit can be as shallow as 6 inches deep in this approach, and the individual conducting wires inside should be labeled with a “W” to indicate they are waterproof. For example, THWN-2 wire is a common type for passing through underground conduit. For this application, use thick-walled conduit with a minimum diameter of 3/4 inch. For underground applications, never utilize thin-walled EMT conduit.

Wire runs through Schedule 40 PVC conduit. The conduit must be at least 18 inches deep in this case, and the individual conducting wires within the conduit must have a “W” waterproof rating, such as THWN-2.

UF cable is routed through metal or PVC conduit. Although it is uncommon, running UF cable (but NOT NM) cable via metal or PVC conduit in an underground application is permissible. However, until the conduit is at least 3/4 inch in diameter, it can be difficult to fish cable through it. Because it is easier, most electricians prefer to fish individual watertight THWN wires through conduit.