New electrical circuits are added when adding additional electrical outlets or lighting to your storage shed or finishing a basement. The number of circuits depends on how many lights or outlets you are installing.
Adding a new circuit is done to run a new electrical line from your houses electrical panel out to your storage shed or if you already have a electrical sub panel in your garden shed you can pull the new circuit from there. Your shed plans may included drawing of the panel location in your shed.
Safety: If you don't feel comfortable working with an electric panel or have a concern with any part of working with electricity you should consult a licensed electrician. You may even run all the wiring and then get an electrician to review your work before covering it up. Your local codes may require you to hire a licensed electrician.
Turn off the main breaker that supplies power to the panel you are working in. This breaker will either be outside at the meter or at the top of the panel you are working on or at another panel that feeds the panel you are working on. This is common in back yard sheds where the main panel is on the house and is feeding the sub panel in the shed. Whichever way it is set up, make sure the power is shut off and double check that it is off. Use a proximity tester to verify that the circuit you are working on is actually turned off.
Open the Panel so you can assess what you will be working on.
Figure out which side of the panel box you will come into the panel. Notice the knockout holes on the top, bottom and sides of the box. There are several sizes of knockouts available to use. Pick one that matches your 1/2" cable connector.
Remove the knockout that you want to use and that is the same size as the cable connector. Install the cable connector and tighten it onto the box using the serrated nut. After you get it hand tight use the hammer and flathead screwdriver to tighten it. Place the screwdriver on the large teeth and hit the screwdriver with the hammer.
Feed the new cable into the box thru the cable connector. Pull enough cable into the panel to comfortably route the wires along the sides of the panel to their respective locations. The cables in most panels are usually organized, try to follow the same cable routes as close as possible, it keeps the panel safer and easier to understand next time you have to work on it.
Tighten the cable clamps onto to secure the cable then cut the sheath off the cable on the inside of the panel about 1 inch into the panel.
Strip 1/2 inch of sheathing from the end of the black and white wires and then make the wire connections in the panel as follows: