How to Add Circuit Wiring to a House

Lay out the circuit on paper before you begin the installation. Add up the expected load of all the devices you plan to install so you can decide what size of circuit breaker and electrical cable to use. If the load exceeds 10 amps, use a 15-amp breaker; if it exceeds 15 amps, use a 20-amp breaker. If you need a 20-amp breaker, you'll also need 12-gauge cable. For smaller breakers, you can use 14-gauge cable, although 12-gauge cable is preferable.

Install electrical boxes for all the devices you plan to install. Cut a hole in the drywall with a drywall saw for each box and nail it to a stud or ceiling rafter. Make each hole large enough so you can work comfortably. It isn't difficult to repair the drywall after you are finished wiring.

Run electrical cable between each box and from the last box on the circuit back to the panel. Instead of cutting drywall so you can install cables behind it, drill a 1/2-inch hole in the top or bottom plate of the wall, then feed the cable into the attic or basement and run it laterally. Feed it through another 1/2-inch hole in the wall plate and run it vertically to the next box. Staple the cable to framing in the attic or basement with wire staples.

Pull enough cable through each electrical box so you can make connections to the appropriate devices. After stripping the wires with a utility knife, connect each device by following the standard color code for wires and electric terminals. Black wires always connect to brass terminals, white wires to silver terminals and bare ground wires to green terminals. When you splice two or more wires together, they must always be the same color.

Make the connection in the panel after you have wired all the devices on the circuit. Be sure to turn off the main panel breaker before you unscrew the cover in preparation for wiring. Remember that the brass bus bars in the panel remain energized even when the breaker is off, so keep your hands and tools away from them.

Feed the cable through a knock out hole in the panel and pull enough through so you can make connections. Strip the cable sheathing, separate the wires and remove 1/2 inch of insulation from the ends of the insulated wires.

Loosen a vacant lug on the silver bus bar with a screwdriver, feed in the end of the white wire and tighten the lug. Connect the ground wire to the ground bus in the same way.

Unscrew the lug of a circuit breaker with an appropriate current rating for the circuit and feed in the end of the black wire. Tighten the screw and give the wire a tug to make sure it's secure. Snap the breaker into an available slot on the front of the panel. Turn off the breaker.

Replace the panel cover and affix a label identifying the circuit to the cover or the panel door. Turn on the main breaker, then turn on the breaker for the circuit you just wired. It should stay on. If it trips, turn it off and inspect your wiring for loose or miswired connections.