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How to Run a New Electric Circuit from a Breaker Panel

How to Run a New Electric Circuit from a Breaker Panel

by Fred Fauth (email Fred) | | January 10, 2013 | 26 Comments »

Running a new electric circuit is a pretty simple task that can be accomplished with a little bit of effort, care, and the right tools.

This article is focused on running a new circuit for light fixtures or outlets. The same principals apply to all 110V circuits, and slightly modified instructions can be used for 240v circuits.

Tools & Materials Required to Run a New Circuit

  • Wire strippers.
  • Pliers or wire cutters.
  • 14/2 or 12/2 Romex wire in the length required (see below).
  • Electrical boxes.
  • Receptacles.
  • Wire staples.
  • Hammer.
  • Phillips and flat head screwdrivers.

Electric Code & Regulation Concerns for Running a Circuit from the Breaker Panel

installing-a-new-receptacle

To meet code in most areas you must obtain a permit and have your work inspected by the local electric inspector. In some jurisdictions you can only perform this work if you are a licensed electrician, even if the work is in your own home. Check your local government’s web site for details.

Almost all jurisdictions enforce either the 2005 or 2008 National Electric Code (NEC). You can read the 2005 and 2008 NEC online for free, just follow the instructions in that article for how. If you’re new to electrical work or looking for some helpful guidance, we highly recommend picking up a good instruction manual. We’re big fan’s of Stanley’s Complete Electric, a resource we regularly turn to for help that is much simpler to follow than the NEC.

Remember, only tackle jobs you are qualified to perform. And as always, if you use our instructions, you do so at your own risk.

15 or 20amp Circuit: Select the Right Wire for the Amperage

Lighting and receptacle circuits in a house are 110v, 15-amp, or 110V, 20-amp. For 15-amp circuits, 14/2 (meaning, 14 gauge, 2 conductor) Romex is appropriate. For 20-amp, 12/2 Romex is appropriate. Note that 14/2 and 12/2 wire will actually have 3 wires inside: a black, white, and ground wire. Remember, as gauges go up, the size of the wire goes down. Do not install a breaker that is too large for the wire. (E.g., do not install a 20amp breaker on 14/2 wire). This is unsafe and could lead to a fire.

For most installations, 15-amp circuits are appropriate. The code requires 20 amp circuits in kitchen appliance circuits and dedicated microwave circuits, as well as in a few other scenarios. You might choose to install a 20 amp circuit in a garage or workshop to handle additional load. Otherwise, 15 amp circuits are appropriate for lighting and outlet circuits.

Running Romex Wire for a New Circuit

Running Romex on studs and joists is pretty simple: Start with the coil of wire at the breaker box. Run wire along side of, or through studs to the first outlet or fixture, and and then run the next strand of Romex to the next outlet or fixture, and so on. Each outlet serves two purposes: to provide power to devices plugged into that outlet, and to bridge the circuit to the next outlet in the line. Leave enough wire on the breaker panel side to run the whole length of the panel. (E.g., if the wire enters the panel at the bottom, leave enough wire to reach just above the top of the panel.)

(Note: Even though it appears that house wiring is serial, it actually is not. House wiring is always in parallel. If a house were wired in serial, current would only pass to the next outlet when a device was plugged in and running on the first. Obviously, that’s not how houses work. If this doesn’t make sense to you, don’t worry about it… it’s a question we sometimes hear.)

Here’s a picture of a typical Romex run through a single gang box. How to wire a receptacle is outside of the scope of this article, but its a pretty simple, straightforward step.

how_to_run_an_electric_circuit

The final electric box will only have one set of Romex coming in:

how_to_run_romex_from_a_breaker_box

How Many Outlets can be Connected to a Single Circuit?

For lighting fixtures, the limit is 80% of the amp limit of the circuit. For outlets, the limit is 8 based on the assumption of 180W per outlet; however, we recommend installing only 5-6 outlets per circuit given the higher demand of today’s appliances and electronics.

Connecting the Circuit at the Main Breaker Panel

To connect the circuit at the breaker panel, you’ll need to purchase a new compatible breaker and have at least one free space in the panel. There are several different brands of panels and corresponding breakers, so make sure you get the right one for your panel. Both Home Depot and Lowes sell the most common brands.  If you don’t have any space in your electrical panel, you can replace one of the breakers with a tandem breaker that will give you an extra slot.

Connecting the circuit to the panel is simple. Remove the front cover of the panel. Remove one of the knock-outs and install a cable clamp in the knock-out to keep tension off the wire. White and ground wires are stripped and connected to the grounding bus, and the black wire is connected to the breaker (usually, via a screw). In most panels, the breaker simply pushes into place, making contact with the hot strip in the back of the panel. Make sure the breaker is turned off before connecting it.

Note: We recommend you turn off the main breaker to the house (the big one, at the top) while installing a new breaker. If you don’t, the two center bars in the back will be energized with enough current to kill you.  Note that even when you turn off the main breaker, the screws at the top of the main breaker and the exposed wire coming in are still energized.

how_to_connect_romex_to_a_breaker_panel

Testing a New Circuit

After you snap in the breaker, ensure your work is clean and double check your wiring. When you’re confident everything is set, turn on the breaker and test your new circuit using a circuit analyzer or professional multimeter (review).

What do you think? Have you ever run a new circuit? Let us know about your experience.

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Conversation on This Article

26 Responses to How to Run a New Electric Circuit from a Breaker Panel

  • Baba responds...
    October 12th, 2009 11:29 am

    Thanks! We’ll be doing a lot of this soon at the Stone House.

    [Reply]

  • Fred responds...
    October 14th, 2009 10:17 pm

    You’re most welcome! I hope lots of folks find it useful.

    [Reply]

  • edward howell responds...
    February 11th, 2010 6:00 pm

    Can you run a 12/2 wire from the panel box to the outlets or switches and the run 14/2 wire off of the outlets or switches to other outlets or lights on a 15 amp breaker?

    [Reply]

  • Fred responds...
    February 14th, 2010 4:13 pm

    Edward, I don’t know that there’s any regulation that would prohibit this (using lower gauge wire for part of a run)… One concern, of course, is that a future electrician decides to replace the breaker with a 20amp thinking the entire circuit is running 12/2. I would be more comfortable if the 12/2 wasn’t the wire that started in the panel…

    Check out the 2008 NEC for a better answer. (There’s a link up towards the top of the article).

    [Reply]

  • Randy Cox responds...
    July 18th, 2010 9:34 am

    I just watched a show on HGTV with a guy named Mike. As a part of a remodel, he found a panel with most of the romex feeders coming into the side of the panel, but about four were coming in the top. He and two electricians said those wires at the top needed to be moved to the side.

    What code was he talking about. I’ve never heard anything like that. Am I missing something?

    [Reply]

  • Mike responds...
    July 20th, 2011 5:37 pm

    How far can you safely run a new line? I need to move my welder to my garage, probably 100′ from my current 240 recepticle, in the utility room. I am thinking that I will need another smaller breaker box on the other end to be safe, but what guage wire, and is this too far? I am asking about the distance, because I have always been told that too long of an extension cord would cause a loss of voltage.

    [Reply]

    Fred Reply:

    Mike, that question’s going to need to be fielded by a qualified electrician. Unfortunately, it’s beyond us here. You could try http://www.ezdiyelectricity.com/ for an answer maybe.

    [Reply]

  • Arsenio responds...
    February 11th, 2012 1:34 am

    Can I run stranded wire #10 gauge from control panel with 20 amp breaker since the wires already there maybe left by the electrician under the house 4ft high. Then I have to put the junction box at the end because I plan to extend with solid wire #12-2 gauge that run into my Japanese tea house from the backyard with 3 outlet and one light. The out let maybe will have to use mostly laptops, electronics gadget and electric heather (oil). Thank you!

    [Reply]

    Fred Reply:

    Nothing in the code would prevent you from using a thicker wire than is required for part of a run…. You get into trouble when you do the opposite – running a thinner wire than is required. The load you describe seems well within the rules for a 20amp breaker and 12/2. Note that I am not an electrician-you should follow the code for your area for all your work.

    [Reply]

  • HANDYMAN51 responds...
    March 30th, 2012 9:30 pm

    Having an electrical background ( simple!), I found your instructions to be very helpful for the average homeowner. Thanks for your emphasis on safety.

    [Reply]

  • Steve Nelson responds...
    July 20th, 2012 12:48 am

    When running 12-2 wire from my house to a garage for just 3 lights and 3 outlets using 110 volts, can I use a Square D QO service panel for the 110 volts circuit breakers? Thank you.

    [Reply]

  • Matt responds...
    September 17th, 2012 10:27 am

    I recently had to rerun a wire for my dryer in order to get a grounded wire to my outlet and my dad gave me one great piece of advice. When you put the circuit breaker into the box, keep one hand in your pocket. The thought is that you won’t accidentally grab two poles and connect the circuit with your body. I took it one step further and wore insulated gloves. The last piece of advice I have is take your time. Trying to go quickly is a recipe for disaster.

    [Reply]

  • Brian responds...
    October 8th, 2012 3:57 am

    How low can I run a wire thruough a wall. Reason I am asking is I drilled a hole through a new stud wall to go under the outlets (6″ off subfloor) and run up to each one. Want to make sure I am not doing anything that I will fail for. Thanks in advance for your response.

    [Reply]

    Fred Reply:

    Brian, you should be able to find code limits for cable length, but I’ve never seen this as a problem in most regular-sized homes on a reasonable circuit. I would think the limit is greater than 250 ft., but I am not sure.

    [Reply]

  • John Starkey responds...
    October 12th, 2012 4:13 pm

    I was wondering how many 12-3 conductors can be used in one staple. It is my understanding that it depends on the size of staple and manufactures recommendations. the only thing on this subject I could find in the NEC was on 334.30

    [Reply]

  • jeff_williams responds...
    January 10th, 2013 8:30 am

    One thing to note, if wiring the circuit to a sub panel, ground and neutral must be on their respective bus bars. Only in the main panel can they be mingled.

    [Reply]

    Fred Reply:

    Jeff – good add. I have this in the article linked on “main breaker panel” but not here. If you are working in a subpanel you have to keep neutral and ground on separate buses.

    [Reply]

  • Reuben responds...
    January 10th, 2013 12:55 pm

    Nice tutorial. keep up the good work.

    [Reply]

    Fred Reply:

    Muchas Gracias!

    [Reply]

  • poiboybf responds...
    January 10th, 2013 1:07 pm

    Thanks. I always like how clear you make these. On a somewhat related but different note, an awesome (read: useful to me) article would involve an explanation of how to add a second switch to an already existing bank of lights. I use my bulkhead often, but when I exit through it I have to either leave the basement lights on, or fumble around in the dark for a little to open it. Any easy fixes here (other than to call an electrician?)

    [Reply]

    Fred Reply:

    You have a few options. On the “easiest” front, simply replace the switch with one that uses a remote in addition to the switch, then just velcro the remote somewhere more convenient (or sit it in a place more convenient). These switches usually run around $30 or so at the big boxes. (Obviously, you could do home automation solutions too – but these are going to get very pricey).

    On the more elaborate side, you can convert the switch to a three way switch. We haven’t done an article on that, but it’s not too hard. There are two ways to wire a standard switch, and each of these two ways has a way to modify it into a 3-way switch, but that involves running romex through the wall to another switch location – not always the easiest solution if the drywall is already up.

    Jeff Williams might have some additional thoughts on this too – he always seem good for ideas on this type of thing. We’ll add this to the list of projects we might do an article on.

    [Reply]

    jeff_williams Reply:

    There’s a great Family Handyman article that explains it (with diagrams) way better than I ever could. Basically you have to run three wire from the existing switch location to the new switch location. http://www.familyhandyman.com/DIY-Projects/Electrical/Switch/how-to-wire-a-threeway-switch/Step-By-Step

    [Reply]

  • bigredmachine responds...
    January 10th, 2013 4:09 pm

    You guys always have very helpfull info. How far back can I go to find articles I might need in the future.

    [Reply]

    Fred Reply:

    You can look through our stable of “How To” categories linked at the top of every page.

    [Reply]

  • trebor responds...
    January 13th, 2013 9:39 am

    Hmm I wish these would come through my reader so I would see them. I think the rrposts don’t (at least not in Google Reader anyway).

    But this is a seriously helpful article. I’m just about to close on a house and I see a few places where I’ll need to do some work like this. Hopefully with a great article like this (and an engineering friend) I can do it myself!

    [Reply]

  • theDIYvillage responds...
    January 14th, 2013 10:06 pm

    Glad to find this post! I’ve found that 2013 must be the year of needing more power…The garage/workshop is first on the list and I will definitely be revisiting to make sure I’m not skipping over any steps! Thanks Fred!

    [Reply]





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