Wiring a Breaker
Label each wire coming into the breaker box to indicate where the circuit is, what is on it, and what size breaker you will install. Write this information on masking tape and attach it to each wire so you can label the breakers. It is best to label them when you install them or when you take the old box out during an upgrade.
Pull the wires down through the conduit into the top of the box and spread them out so each label is readable. Select the wire you want to attach to the first circuit.
Select a circuit breaker with the correct amperage. Typical household circuits are 15 or 20 amps, depending on how many items are on the circuit. Use a screwdriver to loosen the screws at either end. Insert the black wire into the front or inside end of the breaker and the white wire to the rear or outside end. Tighten the screws with the screwdriver.
Organizing the Box
Insert the breaker into the top slot of the breaker box. Press the front or inside connector down first, until it snaps in place, and then the rear or outside connector.
Fit the green wire from the same cable into an empty hole in the ground block, at the top of the circuit breaker box, and tighten the screw near it to lock it in place.
Continue wiring breakers in the same way, listing each circuit on the chart on the inside of the door with the number of the breaker bay and the area of the house it covers, until you have wired in all the cables.