How to Wire a Breaker Box in 12 Steps

Electrical knockouts are designated spots that can easily be opened to allow access for new wiring. Each knockout consists of a circle in the middle that’s surrounded by several rings. When removing knockouts, start from the center and work your way outwards. On one of the sides of each knockout is a small marking or indentation. 

To remove knockouts, place the tip of a flathead screwdriver on the opposite side and hit it with a screwdriver to open the knockout and use pliers to remove it. You’ll need to open several knockouts for several wires: one for the main service wire, one for each branch circuit, and another for the main grounding wire.

Next, an electrician will choose the most ideal spot for mounting the circuit breaker box to the wall. If the main service wire enters your home through a metal pipe or conduit, the opening at the top of the electrical panel needs to be installed carefully aligned to it. Use a pencil or electrical tape to mark the spot where you’ll need to drill, and make sure the panel is evenly placed by placing a level on both sides and on top and bottom. Then, use a drill and the electrical screws that came with the breaker box to secure it to the wall.

In general, there are three main service wires: two hot wires (which are either black, red, or both) and one neutral wire (which is always white). All three of these wires need to be pulled through the conduit and into the breaker box. You have to attach these wires to the end of a fish tape with a bit of electrical tape, then insert it through the conduit opening outside the home and push it through into the breaker panel. This is usually a two-person job as someone needs to be pushing it from outside while the other pulls it into the breaker from within.

The grounding wire is a bare copper wire that connects to a grounding rod outside and allows electrical systems to safely dissipate electricity into the earth. Like the main service wires, this one will need to be pushed through the metal conduit and into the breaker box with a fish tape. You will then connect the grounding wire to the grounding bus bar, a copper metal strip that can be found on both sides of the electrical panel.

Next up, attach the main service neutral wiring to the neutral bus. The location of the neutral bus in the electrical panel varies, but it’s always far from the hot bus bars and consists of a thin metal bar with many screws and a large opening for the main wire.

Electrical panels contain circuit breakers with voltages ranging from 120 to 240. This component both connects both of the black service wires to the hot bus and controls all the electricity entering your home. You’ll need to remove a small amount of insulation from each black wire to expose the bare wires inside, then place those wires into the corresponding openings in the main breaker. You shouldn’t leave any wires exposed as doing this can pose a safety risk when the panel is active. Lastly, use a screwdriver to tighten electrical screws holding the wires in place.

Branch circuit wires are additional wiring that’s intended for both general and specialized use. For example, your main service wires may provide 240 volts for appliances while branch circuit wires may only provide 120 volts for something smaller, like an outlet. Branch circuit wires consist of three total wires: one neutral, one grounding, and one hot. Push these wires through one of the knockouts to insert into the breaker box. Once inside, use a cable striping tool to remove a small amount of the outer coating from each wire (except for the grounding wire) to reveal the raw wires inside.

Once the branch circuit wires are in the breaker box, you should then insert the tip of the copper grounding wire into the grounding bus bar and use a screwdriver to tighten the screw that holds the wire in place.

To install a branch circuit breaker, place it in the designated spot below the main circuit breaker and use a screwdriver and electrical screw to hold it in place. Once that’s done, they attach the white, neutral wire to the neutral bus, the black, hot wires to the hot bus, and screw everything into place.

When everything is wired, place the panel on top of the breaker box to conceal the wires and use a screwdriver and electrical screws to secure it. You can now have the utility company turn the power back on and activate all the circuit breakers.

Working one by one, you should test each branch circuit breaker by turning it on and off. It’s also wise to label each circuit breaker so it’s easy to tell which part of the home they will affect.