If you have just built a new garage or have a garage without many electrical sockets or lights, it might be time to think about wiring your garage for electricity. With some basic tools and a bit of electrical knowledge, you can get your garage ready for the tools and appliances you want to operate. Wiring up the garage can be done over a weekend or two. If you want to do the wiring in the garage and leave the main panel connection to an electrician, that's an option.
Turn off the main power at the breaker box. Put on eye protection and other protective gear. Remove the panel cover with a screwdriver or screw gun. Use the tester to make sure power is off, below the main feed line into the breaker box.
Punch out a 3/4-inch hole in the bottom of the main breaker panel cabinet. It is common for the breaker box panel to be located at the side or back of the house. Connect a piece of 3/4-inch conduit, using a connector, to the bottom of the main panel box. Cut to length, using the conduit tubing cutter. Run this down about 18 inches.
Drill a 3/4-inch hole through the wall, right behind where you will install your junction box. Install a small junction box at this point, using another conduit connector. Punch out the 3/4-inch hole, just like you did for the main panel box. Attach the box to the 2-by-4 wall, using drywall screws through the back of the box.
Call the utilities. They will tell you if it is not safe to dig, due to existing buried lines in the area. You must dig a trench to run your electrical conduit from the main breaker box to the garage. Rent a ditch digger and make the trench about 24 inches deep and about 18 inches wide.
Connect a conduit elbow into the hole you made behind the junction box. Run that down into the trench and use another elbow.
Install 3/4-inch conduit in the trench, using connectors as you go. At the garage wall, install a 100-amp or 50-amp junction box. Consult an electrician for help with this step. Mount it to the wall, using a drywall screw, and install another 3/4-inch conduit connector at the bottom of the box. Run a piece of conduit down toward the trench and connect with another 3/4-inch elbow. Now the conduit run is complete.
Run a fishtape through the conduit, from one junction box to the other. The fishtape is a steel wire that helps you pull wires through conduit. At the other end, attach electrical tape to a 1/0 wire strand and attach it to the fishtape. The wire strand will have a hot, neutral and ground wire. Consult a local electrician for exact wire size requirements.
Pull the wire to the end of the conduit, using the fishtape. Leave at least 3 feet of extra wire at each end, beyond the actual junction boxes themselves. Strip back the wire sheathing and connect the wires to the junction box in the garage and the main panel box at the house. Your junction box in the garage will already have a main 100-amp breaker installed. Black wires go to the breaker, neutral wires to the neutral bar, and ground wires to the ground bar. Your main panel box will have various breakers installed based on the exact electrical needs of the garage.
Drill holes in the studs of the garage walls. Run conduit circuits for outlets and lights. Also think of any dedicated runs needed for heavy-duty appliances or tools you might use in the garage.
Install plastic boxes for all of the outlets and switches. Nail them to the studs. Outlet boxes are usually installed at about 12 inches off the ground, while switch boxes are installed at about 48 inches. Run your conduit lines from the junction box to the plastic boxes. Consult an electrician for help with this step if needed. Now your walls can be covered and the electrical sockets and switches will get installed later.
Always consult with an electrician or inspector before doing any electrical work.