How To – Adding Circuit Breakers To Your Electrical Service Box

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    Whether you are installing a home alarm system or running a dedicated line to your new window air conditioner there are times when you will need to add a circuit to your home and that means you will also need to install a breaker in your service box.

    Although this is something that  a knowledgeable home owner probably can accomplish on their own you should understand that an electrical inspection will most likely be needed in most locations.

    Before you begin work you should call or visit your local building official’s website and read the rules about working on your home’s electric service.

    Can Your Service Support More Circuits?

    The first thing that you need to establish is how much power will be required by the new circuit you are installing.

    Standard circuits are usually 15 amps and they can power general lighting, computers and most electronics in our homes.  A 15amp circuit will be wired with 14 or 12 gauge wire and is often able to serve more then one room.

    The next step up is a 20amp circuit that uses 12 gauge wire. When an appliance needs extra power a 20amp circuit can be installed to serve a single outlet receptacle which can also act as a general purpose outlet if the appliance is removed.

    Heavy Demand circuits such as a Stove, Heavy tools such as a Mig Welder, lathe or other items may require a 20 amp or 30 amp dedicated circuit. These circuits can be either hardwired directly to the unit that is being powered or they can be installed with a special receptacle.

    I would not suggest that any home owner install a 220 volt circuit by themselves for a clothes dryer unit or other application. These circuits are a little bit more difficult to work with and should be installed by a qualified electrician.

    Now that you know what size circuit you will need you can inspect your service box and establish if it can support your new appliance or device.

    Service Circuit Breaker Box Rating

    Most homes are equipped with service boxes that are rated from 100 amp to 300 amp with 125 and 200 as the most common.

    Read the rating of the service box in your home and then add up the number of breakers and their ratings in your box. If you are well below the rating of your circuit breaker box then you should be able to add a circuit without the need for a Circuit Breaker Box upgrade.

    Upgrading your circuit Breaker box can be expensive and it is something that the average home owner can not perform on their own because it will require a shutoff of your electric service at your electric meter.

    Purchasing the correct Circuit Breakers

    When you visit your supply center you will be presented with a number of different brands of circuit breakers.

    Take a close look at the design of each manufacturers breakers you will see that they have the same features of a switch and screw hold down for your black hot wire but the back of the breaker is different.

    This means you will need to purchase your breakers from the same manufacturer.

    In addition there are a variety of different breakers that are rated at the same amperage.

    There are standard breaker and arc fault breakers and GFCI breakers that can provide some anti-electrocution features… There are also double breakers with two polls that are joined and double breakers where the two poles are even different amperage ratings.

    Unfortunately the selection of the exact circuit breaker you will need is beyond the scope of not only this howto but our website. Providing the exact breaker information is something that an electrician is trained to do and this is why anything other then a single pole 15 amp circuit should really be performed by a skilled electrician.

    If you are able to get the rating of the breaker you need then the next step is installing the breaker in your circuit breaker box.

    Installing Breakers

    Working inside your breaker box is EXTREMELY DANGEROUS and WILL LEAD TO YOUR DEATH or serious harm. If you do not know what you are doing then you need to hire an electrician. This HowTo can not provide you all the details you need to know to perform this job safely and is only presented as informational to allow you to seek more exact and professional advice.

    The first thing you need to do before you work on your electrical service is turn off the MAIN feed breakers that feed the rest of your circuit breaker panel.

    After turning off the breaker that should be located seperately and at the top of the box and should be a larger physical breaker then the one or two galleys of circuits below it you can remove the screws that hold on the access plate cover.

    Once you have removed the cover you must test your breaker box to make sure the main circuit is indeed turned off and no power is running into your breaker bars. Use a non-contact electrical tester. If you get a positive reading you may need to use a contact grade tester that will not pickup interference from the surrounding voltage.

    REMEMBER Power is still coming into your box prior to the main circuit TURNING OFF THE MAIN CIRCUIT WILL NOT REMOVE ALL POSSIBILITY OF ELECTROCUTION.

    If you are using standard 2 wire with a ground romex then you will need to feed the wire into the box from the top or side access hole. Remember whenever you feed in a new line it must be secured with a screw down at the point it enters the box. The white Shielding protecting the three wires on the romex cable must be stripped back about 2 feet to expose all three wires however the white and black wires must not have damage to or their shielding removed.

    You want to strip the ends and install your ground and white neutral wires first to the side poles.


    At this point you are ready to install your new breaker.

    Install the new breaker in the same configuration as its neighboring breakers.

    The attachment point for the black wire will be to the outside of the center of the box.

    The circuit breaker is notched on one end and has prongs on the other.

    Install the notched end first and rock the breaker into place.

    When the breaker is seated you should feel it snap into place and it should be flush with its neighbors.

    At this point you can attached the stripped end of your black wire to your new circuit breaker using the hold down screw.

    You should position the new wires that you have just installed in a orderly manner to match the wires that your electrician installed. This means make sure they bend in similar ways and are out of the way of each other without overlaps or feeding under.

    Since you are testing a new circuit for the first time you should position all other circuit breakers to the off position.

    Your new breaker should already be in the off position.

    Turn the Main Breaker back on and it should power only the new circuit you installed.

    Listen for humming and inspect the service at the Circuit Breaker Box and have a helper test the outlet at the end of the circuit where your receptacle is already installed.

    Final Note

    This HowTo should not be used for instructional purposes.  Installing electrical service in your home can be dangerous and can lead to your death. It can also cause fires long after you think the job has been performed correctly.

    You should be trained on site by a professional to perform this work. If you do not have the proper hands on training then seek out a local technical school with evening or weekend classes or find another way to be trained by someone who knows how to perform this work on a professional level.

    Or Hire an electrician.

    The YouRepair Store sells a full line of Electrical Tools, Testers, Circuit Breaker Service Boxes and Breakers. Check the prices and look for free shipping on most orders over $25.

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