Using an Equation to Help Plan Electrical Circuits Wire Sizes and Breakers

So I had some people reach out to me and they were asking me kind of for a list of what they should use for certain applications in their home as far as lights and as far as outlets. This is my recommendation only because I do these videos for homeowners. And so if you just have a typical home, nothing like a shop or no type of commercial application, then if you're going to run lights or a ceiling fan, then just use 14 gauge wire, which is this white jacketed Romex, and use a 15 amp breaker with a 14 gauge wire. This is really important because this 15 amp breaker is specifically sized for a 14 gauge wire. For your outlets, you're going to use 12 gauge wire, which is this yellow Romex with a 20 amp breaker. You can certainly use a different, you could use a, say a 15 amp breaker with a 12 gauge wire. So the wire is oversized. You're just kind of wasting money, but you certainly couldn't use a larger amperage breaker with a smaller gauge wire. So a few videos ago, I was wiring the three-way and four-way light circuits. And so you'll see that the Romex I have here has two conductors, has a black wire and a white wire, and it has the copper conductor. And there were obviously more, there was the red wire, more conductors than the Romex that I was using for the three and four-way circuits. So when you're just wiring up regular lights, just a typical light switch, all you're going to use is this Romex with the two conductors and the copper ground. For all my outlets today, I'm going to be using the 12-2 wire, 20 amp wire. And all it's going to have is the black wire and the white wire and the ground. So your outlets and switches, they also have amperage ratings. For all of my lights, I use 15 amp wire. So it was the 14 gauge wire with 15 amp breaker. For all my outlets, they're all going to be 20 amp. And so I got the outlets and the ground fault circuit interrupter outlets that are rated for 20 amps. So they do make some of these that are rated for 15 amp. You don't want to use those on this circuit. You want to make sure that whatever device you have, if you only have a 15 amp device or 15 amp outlet or 15 amp switch, you want to make sure that your breaker is also 15 amp. So if you were to install a bunch of these in a circuit and even one of these was only 15 amp, you'd want to use a 15 amp breaker to power the circuit. So regarding how many outlets you can put on a circuit, the answer is actually 10 by code. It might be different in your municipality or in your area. I've talked to a few guys where they say they only use eight. So some people say eight. And my rule of thumb is what am I going to be running? And so of course, people that do this as a trade, they're going in and installing the wire to spec. So they have somebody else doing the calculations and then they're just putting it all together. But for a homeowner, this is something you might want to consider. Do you really want to put a bunch of outlets on one circuit or can you get away with fewer outlets? And so if you're going to wire a garage, of course you wouldn't want to just put the maximum number of outlets on the circuit. You may be able to get away with five and it would be just fine. And there are codes to how many outlets you do have to have in a room of a certain size and you can look those up online. So if you're trying to determine how many outlets you should put in a bedroom, maybe you might just want to put, say, one on each wall or if you have a pretty long wall, maybe put another outlet on the wall and you're still going to be within the 10 outlet limit. When I'm installing circuits like I'm going to be doing in the garage, I'm actually thinking about what I'm going to be running. And so what I use to determine that or how many outlets I should put on a circuit, what I use to determine that is I use a formula, watts equals volts times amps. And you can generally get the wattage off from the main plate on your device. So you might have a toaster and it might be 1,200 watts or a microwave might be 1,100 or 1,200 watts. And so let's just use that as an example. Let's just say we're going to run a toaster, just as an example. So if we have 1,200 watts, we know what the voltage is because we're using a 120-volt circuit in our home. And now all we have to do is figure out how many amps we're going to run. And why this is important, as you saw earlier, I talked about a 20-amp circuit. And so obviously we don't want to draw more amps than our circuit is capable of carrying. And with a 20-amp circuit, it's generally going to trip. Your breaker is generally going to trip somewhere around 16 amps. So really you want to be figuring on what can I run and get somewhere up to about 16 amps, which is 80% of the capacity of the circuit. So with this formula, you see how it wasn't easy to calculate amps, how I had it written before. So let's rewrite this as watts divided by volts equals amps. So if you want the nightmares of high school algebra to come back, I guess I can show you how I came up with this. But if you want, just write this formula down. So if you want to calculate this yourself, and some lecturers are going to tell you, well, that's not a perfect formula. But this is going to get you close enough to make sure that you size your outlets properly. So let's go ahead and do an example. Let's say you're going to wire your kitchen. So let's say that you're going to have a toaster. So we'll say 1,200 watts. And let's say your wife's into baking. She has some sort of bread maker. Let's just say that that's, I don't know, 1,000 watts. And let's say that she also is going to be using a mixer at the same time. Or let's just say we're going to have a busy day, and we're also going to have a microwave. Kids want to microwave something. So let's say we have another 1,200 watts. So if we add all this up, we get 3,400 watts divided by 120 volts. So how many amps are we going to draw on the circuit? So I'm getting something around 28 amps, which is obviously way too much for the circuit. So something you might want to consider is, I have a 1,200 watt microwave. Maybe I want this on its own outlet, on its own circuit. So maybe you will run a dedicated circuit from your panel box up to your microwave. And usually, some of these outlets actually get installed up inside the cabinets, just to hide them, because they're up above a stove or something like that. And so now you still have your bread maker, and you still have your toaster. So now, you might want to separate these out and say, OK, maybe I'll put two breakers over here, over on the countertop. So now I know one of these can be plugged into the toaster, and the other one can just be some miscellaneous thing. And the bread maker can be over in another section, to where maybe it's on another group of, say, two outlets. And so there might be a few different circuits in your kitchen, but you can use this formula to figure out approximately where you need to be, and how you might want to set up the outlets in your kitchen. So in my garage, I've kind of done the same thing. I'm going to have a dedicated circuit for my air compressor. I kind of have my little welding area over there, to where I'm only going to have a couple outlets. So if I want to run a grinder and something else, I'll be able to run those simultaneously. Up above my workbench area, I'm going to have three outlets, but nothing big is going to be plugged in there. So just a few little outlets here and there. But where it actually matters, I've made sure that I've separated out my circuits. So definitely where I'm going to need a division of the power and the amperage on a circuit broken up, I've definitely thought that through to make sure I don't overload a circuit. My last video, I showed how you look at these ground fault circuit interrupters in a circuit. And I'm going to need to use these since this is a garage. I'm going to need to use these first in every circuit. And then after that, I showed how you can use just regular outlets, and they can all be protected. But these are really important to use in a lot of places. So in your kitchens, you want to use them. Your bathrooms, you want to use them. Obviously, out here in the garage, if you have a regular garage in your house, any place outside, you definitely going to need to use these. So I hope this video has helped you understand what size of breaker goes with what size of wire and what size of circuit you should use for your lights, for your outlets, and for your ceiling fans. And when running your own outlets, I hope you find that formula useful. So I'm looking forward to getting the outlets ran in this building. Look forward to that video here in a couple of days. And we greatly appreciate everyone who has supported our channel. I hope to see you in the next video.