The convenience of electrical sockets and lighting in your garden shed is easy to imagine. You'll have a place to plug in rechargeable tools, power electric yard tools like trimmers and hedge cutters, and sufficient lighting inside so you don't bang your head or stub your toe.
Decide the best route to deliver power to the shed. Tap into an existing exterior outlet or add a new circuit for the shed.
Dig a trench, 18 to 20 inches deep and lay the underground cable. Bring the cable up through the floor plate of the shed wall and into a junction box secured to the wall. Fill the trench once the cable is laid.
Determine where you want the outlets, light switch and light. Install each box with screws or nails.
Run sheathed cable from the junction box to your interior outlet box. From there, run to your exterior outlet box and to your light switch. Lastly, run the cable from your light switch to the light fixture box. Avoid having more than three cables enter or exit from any one box. An y more and your box will be too full.
Fasten the cable within 18 inches of each box. Strip the outer sheathing from the cable, leaving a quarter inch protruding inside the box. The insulated wires should protrude from the box at least six inches.
Make your connections. For each, strip 3/4 of an inch of insulation from the white and black wires. In the junction box, use the side cutter to twist ground wires together and cap with a wire nut. Do the same with the stripped ends of the white and black wires. Connect white to white and black to black. Put a cover on the junction box when you are finished.
Wire the outlets. For each, form a bare terminal loop in the copper wire. Fasten the white wire to the silver terminal on the outlet. If a second wire leaves the box, wire that one to the outlet as well. Be sure to twist together the ground wires and fasten them to the ground lug as well.
Wire the light fixture by attaching the white cable wires to the fixture wires using wire nuts, or attaching the cable wires to the fixture terminal screws. Put the fixture in place on the box. At the switch, attach the black wire from the fixture to one terminal on the switch. Attach the other black wire to a switch terminal as well. Twist the two white wires together and cap with a wire nut. Be sure to connect the ground wires.
Connect the underground cable to your power source. Be sure to turn the power off first. Once connected, turn the power on and test your work.
Depending on how your shed is built, you'll want to run your wiring accordingly. The easiest route may be to bring your supply in from the floor, up to a junction box on the wall. From there, go straight up to an outlet box. Branch from there to the light fixture, and the light switch. Since the light switch is by the door. You can run one branch down and back outside for the exterior outlet box. An outlet box on the wall behind a potting bench or workbench, or near a shelf is a good idea. You can plug in your rechargeable tools easily that way. Be sure to check local building codes and obtain permits, if necessary. Sheathed cable needs to be fastened fairly close to each box. Don't skip this step. GFCI outlets may cost a bit more, but they are well worth it in terms of safety. Be sure your exterior outlet is this type, and it is a good idea to make your interior outlet GFCI as well. That way, you can feed your light switch from the GFCI and that will be protected too.
The procedure outlined here assumes a prior knowledge of home wiring and wiring systems in general. Although easy enough for most beginners to complete, this procedure should only be performed by persons comfortable with wiring and working with electricity. If you are not comfortable working with electricity or have any doubts about your ability, hire an electrician. Always turn power off and test to make sure it is off before exposing wiring or making changes to it.