Installing a New Circuit

Installing a New Circuit

The receptacles, light fixtures, appliances and switches in your home are all part of multiple electrical circuits, which begin and end in your circuit breaker panel. For example, all the receptacles in a bedroom might be part of one circuit, wired to a single breaker.


For simple additions, such as installing an extra receptacle, you may be able to extend an existing circuit. As long as adding the load doesn’t exceed the circuit breakers amperage rating, you can splice wires leading to the new receptacle to the circuit’s existing wire. But if you’re wiring a new room or installing a high-wattage device like a major appliance, you need to add at least one new circuit, with its own circuit breaker in the breaker panel.


Always consult local building wiring authorities before working on your household electrical circuit. New circuit wiring must meet local electrical code standards, and you may need to acquire a permit. Additionally, both your plan and the finished work may need to pass an official inspection, and local authorities may require that a professional electrician handle certain parts of the job.


To install a new circuit, you will need an open slot in your breaker panel for a new circuit breaker. Plan to work during the daytime, as you will need to shut off all power in your home during most of the project.  




• Select a circuit breaker designed to handle the load on your new circuit and designed to fit your 
  breaker panel model. Refer to our Circuit Breaker Buying Guide to learn more.




• If you aren’t comfortable working with electricity, have a licensed professional install the new 
  circuit for you.
• When working with an electrical circuit, always shut off the power at the main breaker panel. 
  Leave a warning note so that no one switches the power back on while you’re working.
• When working on the breaker panel, wear rubber-soled shoes, only use tools with rubber 
  insulated handles, and never stand directly on a damp floor.




• Install new electrical cable, boxes, devices and a circuit breaker yourself and save.




Step 1: Plan the Circuit

Plan the Circuit 1. Measure the room or rooms where you’ll be installing the circuit, and draw a
    detailed, accurate floor plan. Make multiple copies, so you can start over
    with your circuit plan if you make mistakes.

2. On the floor plan, mark the position of every receptacle, switch, fixture and major
    appliance you plan to add to the circuit.

3. Draw lines representing the electrical cable for the circuit. The electrical cable
    should begin in the breaker panel and run to every device in the circuit.

4. Add up the wattage for all the devices you expect to connect to the new circuit.
    This will give you the new circuit’s total load.

5. Determine what type of circuit breaker you need to install, based on the total circuit
    load. All circuit breakers have a safe load capacity rating. For example, a 15-amp
    circuit breaker has a safe load capacity of 1,440 watts and a 20-amp circuit has a
    safe capacity of 1,920 watts. If you expect the total load will be greater than 1,920
    watts, you will need to install two separate circuits. Permanently installed
    appliances, such as A/C units, washing machines and ovens, require their own
    dedicated circuit. Refer to our Circuit Breaker Buying Guide for specific guidelines
    on matching different loads to breaker types. Consult an electrician if you are
    unsure of your total circuit load.

6. Verify that your breaker panel can handle a new circuit. Your breaker panel’s
    amperage rating will be listed on the main breaker. Newer homes will have a 100-
    amp, 150-amp, or 200-amp rating, while some older homes may have a 60-amp
    rating. The rating tells you how much total current each of two vertical columns of
    individual circuit breakers can deliver at one time. Any long lengths of wire over
    100 ft. can experience amperage loss, consult a wiring book or electrician for
    more information.

Step 2: Install Electrical Boxes

Install Electrical Boxes 1. Consult your local electrical code for regulations on how and where you can install
    new-work or remodeling electrical boxes. The local code may also require specific
    types of electrical box for certain applications.

2. Select the electrical box you need for every receptacle, switch and fixture in your
    new circuit. Our Electrical Box Buying Guide explains the functions of the different
    box designs.

3. Shut off the main power on your circuit breaker panel before you begin installation
    work, in case you come into contact with existing electrical cable behind your walls.

4. Install the appropriate electrical boxes for every device in your circuit, as laid out in
    your circuit plan.

    a. If you are adding a circuit to a room with unfinished framing, you can mount new-
        work boxes directly to wall studs or ceiling joists.

    b. If you are adding wiring behind existing drywall, you will need to cut openings in
        the wall or ceiling and install remodeling boxes, also known as old work boxes.
        Refer to our Installing Remodeling Boxes Project Guide for installation

Step 3: Run Cable to Devices

Run Cable to Devices 1. Be sure to select cable that can handle the load on your new circuit. Consult your
    local electrical code for specific guidelines.

2. Run cable between electrical boxes, as laid out in your circuit plan.

    a. If you are adding a circuit to a room with unfinished framing, drill 5/8 in. holes
        through wall studs, and pass the cable through the holes. Typically, cable
        should run in a straight line, one foot above your receptacles, but consult your
        local electrical code for specific regulations. Secure cable to framing members
        using cable staples. Screw protective metal nailing plates to the framing
        members at each point where cable passes through. These plates will prevent
        someone from accidentally drilling into the electrical cable in the future.

    b. If you are adding a circuit in a room with finished walls, you will need to use fish
        tape to run cable behind the walls, from electrical box to electrical box. The
        simplest approach may be to run cable up into an attic or down into a
        basement. Refer to our Installing Electrical Cable Behind Walls Project Guide
        for detailed installation instructions.

3. Run cable from the first electrical box in the circuit to your breaker panel location,
    as laid out in your circuit diagram. Do not wire the cable to your breaker panel at
    this time.

4. At each electrical box, wire the cable to the receptacle, switch, fixture or appliance
    specified in the circuit plan. Refer to our Electrical Project Guides for specific
    instructions on installing different devices in a circuit.

Step 4: Run Cable to the Breaker Panel

Run Cable to the Breaker Panel

Inside the breaker panel, you’ll find a grounding bus bar and a neutral bus bar on 
opposite sides of the panel. Each has multiple setscrew terminals for wires. Two hot 
bus bars, which provide electrical power to all household circuits, run down the 
middle of the panel, with breakers on either side of them.

1. Make sure the main breaker switch is in the off position. Before you begin work on 
    the breaker panel, all the wires and circuit breakers in the panel must be de-
    energized. If you have a separate main disconnect, switch it off as well. This may 
    be in a panel outside your house, near the electrical meter.  

2. Remove the screws fastening the breaker panel cover, and pull the cover off the 
    breaker panel.

3. Confirm that power is shut off using a neon voltage tester. Hold one probe against 
   the neutral bus bar while touching the other probe to both setscrews on a 
   double-pole breaker. Note that there are two thick black cables running to the main
   circuit breaker. Be careful to never touch these cables, which are always energized.

4. Remove one knockout slug from the side of the breaker panel. First, use a 
    hammer to tap the knockout slug with a screwdriver. Then, use a pair of pliers to 
    twist off the slug.

5. Insert a cable clamp into the open knockout.

6. Use a cable ripper to strip about 12 in. of sheathing from the end of the cable. Cut 
    off the excess sheathing with a utility knife.

7. Feed the cable through the cable clamp until there is a ½ in. of sheathed cable 
    inside the breaker panel. Tighten the cable clamp to secure the cable.  


Step 5: Wire the New Circuit Breaker

Wire the New Circuit Breaker

For information on AFCI circuit breakers, see our Installing an AFCI Circuit Breaker Project Guide.

1. Insert the end of the bare, copper-colored grounding wire into an open terminal in 
    the grounding bus bar and tighten the setscrew to secure the wire. If it is the main 
    service panel and there is no separate grounding bus bar, connect the grounding 
    wire to the neutral bus bar instead. Position the excess grounding wire so it runs 
    along the inside edge of the panel, away from the bus bars.

120-Volt and 120/240 Volt Circuits:

2. Use a wire stripper to remove a ½ in. of insulation from the white neutral wire.

3. Insert the end of the neutral wire into an open terminal on the neutral bus bar and 
    tighten the screw.

4. Strip away a ½ in. of insulation from the black hot wire. If you’re adding a 120/240 
    volt circuit, strip away a ½ in. of insulation from the red hot wire as well.

5. Insert the end of the hot wire into the terminal on the new circuit breaker, and 
    tighten the setscrew. In a 120/240 volt circuit, connect the red hot wire to the 
    second circuit breaker terminal.

6. Lock the new circuit breaker into an open slot, by slipping the side with the 
    attached hot wire under the tab beside the hot bus bar. Push the other side in, 
    toward the bus bar, until it snaps into place, flush with the other breakers in the 

7. Position the excess neutral and hot wire around the inside edge of the panel, 
    away from the bus bars.

Straight 240-Volt Circuits:

2. Use a wire stripper to remove a ½ in. of insulation from the ends of both hot wires.

3. Insert the end of each hot wire, which will typically be black and red, into a terminal 
    on the new circuit breaker, and tighten the setscrews. There is no neutral wire in 
    this type of circuit.

4. Position the excess hot wires around the inside edge of the panel, away from the 
    bus bars.


Step 6: Replace the Panel Cover and Test

Replace the Panel Cover and Test 1. Use a pair of pliers to remove the breaker knockout on the panel cover that
    corresponds to the position of the new circuit breaker. With a double-pole
    circuit breaker, you will need to remove two knockouts.

2. Replace the panel cover and tighten the screws to reattach it to the panel

3. To avoid a power surge, switch off all the individual circuit breakers before
    switching on the main breaker.

4. Switch on the main breaker and then switch on the individual circuit breakers,
    one by one.

5. Label the new circuit breaker on the breaker panel cover.

6. Test each of the receptacles, switches, fixtures or appliances on the circuit to
    ensure the installation was successful.