Full disclosure: I am NOT a licensed electrician. I can do work on my own house since I’m the owner and it’s my primary residence. I will try to answer questions to the best of my ability based on what I have learned through reading/doing/talking to others who have done this before, but if you have concerns about what you are doing, you should definitely consult a licensed electrician.

So I’m actually at the hooking circuits into the breaker box/wiring them into existing circuits phase of electrical, but for completeness sake, I’ll start at the beginning of my electrical journey. Namely, the part where I got to use those colored pencils I haven’t touched since grade school.

Every good project begins with a plan, and doing any kind of electrical work, especially the kind that involves brand new circuits, is no different. I started my work on wiring for the new section of our house by sitting down with the aforementioned colored pencils and some graph paper.

Well, technically, I suppose I started by reading the National Electric Code twice (and falling asleep trying to read it more times than I can remember). It’s not necessarily a bad idea if you want to start the same way, but I will warn you that it’s very dry, somewhat convoluted (I was constantly navigating back to some previously referenced section to try and discern what they were saying), and mostly irrelevant (unless you have a desire to wire hot tubs, mobile homes, and hospitals). There are a lot of good books out there which will tell you how to wire a room to code. I will try and do that here as well, but I will be speaking from the perspective of the wiring I had to do. The rooms you need to wire are likely somewhat different than mine, so you should definitely consult another reference if you have questions about what you are doing

Once I felt sufficiently armed with knowledge, I began drawing out my circuits. I started by drawing all of the rooms I was going to wire to scale on the graph paper. Though I used one square=one foot, I would actually recommend one square=six inches if you have the space on your graph paper. My drawings got a bit tight at times, and it was sometimes hard to see what I had drawn.

After drawing out the rooms, I added in my outlets. I tried to use the standard electrical symbols when I was drawing since they’re readily available from various sources online and don’t require any artistic skills (of which I have none). So you’ll see the circle with two lines for most of my outlets. Three lines means 220V, and GFCI means it’s a GFCI outlet. However, if you’re doing the wiring yourself, you don’t have to use these symbols. You could draw dolphins and butterflies for your different outlet types if it makes you happy—just don’t expect an electrician to do anything with your drawing except laugh at you.

It seems pretty simple at first to just add some outlets to your drawing, but of course, nothing can ever be that simple. I include the considerations for the rooms I am wiring below. They pretty much run the gamut (laundry room, bathroom, kitchen, living area), so it’s fairly comprehensive. For those of you following along in the National Electric Code, the most relevant sections are 210.11 (mostly C) and 210.52 (see what I mean about their obsession with all those numbered sections? Now just imagine virtually flipping back and forth between those two numerous times—they reference one another quite often without any real context that helps explain what the original section is).

Considerations for various rooms (from simplest to more complex)

Living room/family room

Easily the simplest room I wired. The biggest pieces of code you need to care about is that you need an outlet at least every twelve feet (technically, the code claims any point on the wall needs to be six feet or less from an outlet because it would be too easy to say twelve feet between outlets) and an unbroken wall space 2 feet or more needs an outlet. Note that they measure around corners when counting this.

Downstairs utility room (laundry room)

Officially, you need one circuit without any other outlets for the laundry room. Most people just run a 20A circuit for the washer and, if you have an electric dryer, a 240V, 30A circuit for that. We also have an electric water heater, so I had to run a circuit for that as well. The 20A circuit should be GFCI protected to meet code. Since we plan to leave the bare cement walls for the laundry room, I actually ran all the wires for the circuits through metal conduit and used metal outlet boxes for the circuits down there. Careful if you decide to go this route—the “handy” boxes aren’t technically big enough for an outlet and five 12 gauge wires based on fill calculations. I managed to find slightly larger metal outlet boxes at Menards.

Upstairs half bath

The outlet(s) here need to be on a 20A, GFCI protected circuit that has either nothing else or the bathroom lights only (provided that you aren’t wiring a light/fan combo). You need at least one outlet within 3 feet of the edge of each sink basin. For us, this was relatively simple since it’s a small bathroom where we’re putting only one sink. So a circuit with one outlet and lights on a lighting circuit.

Kitchen

The kitchen is by far the most complicated room in the house. Per code, you need at least two “small appliance” circuits. Basically, this just means you have two 20A, GFCI-protected circuits that have no other outlets on them. The dishwasher needs its own circuit as well (check your dishwasher manual to see what you need to wire this in). You would also want one if you had a garbage disposal, but the old owners actually pulled it out and we don’t want to re-add it since we have a septic system, so that’s not a problem for us. The refrigerator should have a 20A circuit. Generally, you’ll want a dedicated circuit for the microwave as well if you have a wall-mounted one (you can probably get away with plugging one of the small portable ones into a small appliance outlet). And then there’s the range. Technically, some stoves call for 40A/220V, but I prefer to wire for 50A/220V just in case. It’s a lot easier to just switch a breaker if needed rather than trying to rewire to a thicker gauge.

Lighting

You should be able to put most lights on a 15A circuit. You could add them to an outlet circuit as long as it’s not one of the “don’t put anything else on this circuit” ones, but I think it’s cleaner to separate them. This lets you do outlets at 20A and lights at 15A. We’re just wiring into the existing circuits upstairs and doing one new 15A for all of the new downstairs lighting (you can put multiple rooms on one circuit—you just have to be a bit careful with wiring the switches to make sure that turning off the lights in one room doesn’t affect the other).

Connect the dots

Now, take out your colored pencils and play a game of connect the dots. I drew each circuit as a different color to distinguish them. I wrote out the amperage at the end of each circuit and then what type of wire I would need for each section. You’ll notice this picture is a little cramped, thus my recommendation to use a larger scale if possible. It’s also pretty rough and may or may not have some blood stains (turns out wire is sharp). However, it worked for my purposes, forcing me to think through where things would go, what types of wire I would need, and how much.

If you look at the drawing below, you’ll see numbers like “12/2” and “14/3”. This indicates the type of wire to use. The first number is the gauge and the second is the number of wires in the cable. Generally, for interior wiring, you would buy what’s called “NM cable” or non-metallic cable. It’s basically just a number of wires bundled together in a convenient sheathing. So if you buy 12/2 wire, you would have an NM cable with three 12 gauge wires inside.

Yes, you read that right. There are three wires in 12/2 and 4 in 12/3. Why? Because for whatever reason, no one counts the ground when labeling cables (because, you know, it’s not that important). So 12/2 has a hot, a neutral, and a ground. 12/3 has a black, a red (both of which are usually hot), a neutral, and a ground.

Why would you need 12/3 (or some other 3) instead of 12/2? I’ll go through some of the wiring I did in more detail later but at a high-level, I ended up using it in three cases:

1. To wire 220V. There’s only 120V between hot and neutral, so to get 220, you need two hots that are out of phase.
2. Our living room has the top and bottom outlets on different circuits. The top one is actually switched, so this is useful for things like being able to plug in a lamp to the top outlet and a cell phone charger into the bottom one. That way, when you flip the switch, the lights go off but your phone keeps charging. I decided to continue this with the new section, so I needed four wires—one hot for the top outlet and one for the bottom.
3. When I’m putting the lights for two rooms on the same circuit. This gets back to not wanting the second room’s lights to go out when you flip the switch for the first. I’ll go into more detail when I talk about wiring the lights, but the short explanation is that you have one hot wired through the switch for the current room and one hot that’s not for the next part of the circuit. No one wants to go into the next room to turn on the lights for the current one. Please don’t make them.

So after going through all of this, I finally had a rough idea of what I was going to do for wiring (it changed, but we’ll get to that later). Plus it made me really think about what wires go where and get a better list of how much wire I needed to buy from the hardware store. It was also a good double check to make sure we had enough space in our circuit breaker for all the circuits we needed. In our case, we weren’t actually adding many additional circuits, so we ended up being okay, but you should definitely look at your circuit breaker to check the space.

And in addition to space for breakers, you should make sure you have enough amps coming into your home for everything you want to run. You could do a calculation like the National Electric Code suggests, but I will freely admit that I just looked at my panel, saw that we had 200A coming in, and didn’t worry. Why? Well, consider a situation. We have 15 1500W baseboard heaters (yes, I just counted) that could technically draw about 93A total. Let’s say it’s the dead of winter and they’re running at maximum wattage. In addition, I’m in the kitchen with the oven on (10A), mixing some bread in my mixer (4A). Meanwhile, my husband is outside and for some reason, simultaneously using the table saw (15.5A) and the chop saw (15A). And we have gone a bit crazy and replaced all of our efficient LEDs with incandescent bulbs and turned them all on (22.5A). Adding those all up still doesn’t get you to 200A. And yes, I know this isn’t the official calculation but that one tells me 200A is more than enough as well. Also, everyone may notice that one big appliance is not included in my calculations—the dryer. That’s because we don’t use a dryer and likely never will (in fact, the aforementioned table saw actually took over the dryer circuit). It’s the biggest energy hog in our house after the electric heat, and it’s a lot easier to stop using the dryer than the electric heat.

But if you have less than 200A, you may want to consider doing a calculation to make sure you will have enough amperage if you’re adding circuits. A general rule of thumb is that if you have less than 2000 square feet and no air conditioning or electric heat, you’re probably okay with 100A. Otherwise, you may need more.

Obviously, there are a number of other considerations as well and I am not a licensed electrician, so you should consult with one for any tricky situations you have, but hopefully this gives you a good start for planning electrical projects.